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THE PREDATOR EXCLUSION
FENCE MANUAL
Guidance on the use of predator exclusion
fences to reduce mammalian predation on
ground-nesting birds on RSPB reserves
Version 3, October 2019
RSPB Ecology: Graham White & Graham Hirons [email protected]
1
Guidance on the use of predator exclusion fences to reduce mammalian predation on ground-nesting birds on RSPB reserves
Table of Contents How to use this guide ............................................................................................................................. 6
Checklist of important actions before installing and operating an anti-predator fence ........................ 6
Chapter 1. General introduction ............................................................................................................ 7
What are we trying to achieve by the use of predator exclusion fences on reserves? .................. 7
Is predation a problem? .................................................................................................................. 7
Why use predator exclusion fences? .............................................................................................. 7
To install a fence or not? ................................................................................................................. 7
Main target species to benefit from anti-predator fences ............................................................. 8
Do predator exclusion fences work? ...................................................................................................... 8
The effectiveness of fences in increasing nesting success .............................................................. 8
Effect of fences on lapwing productivity ........................................................................................ 9
Effects of avian predation on lapwing productivity within fenced areas ..................................... 11
Do birds prefer to nest inside predator fences? ........................................................................... 12
If productivity at a site is maintained above maintenance levels do numbers of breeding lapwing
increase? ....................................................................................................................................... 13
How effective are anti-predator fences compared with other predation management options?
...................................................................................................................................................... 15
Chapter 2. Deciding whether to install a fence and the fence type ..................................................... 19
What are we trying to achieve by the use of anti-predator fences on reserves? ........................ 19
To install a fence or not? ............................................................................................................... 19
Main target species to benefit ...................................................................................................... 20
Fence design appropriate for specific predator species ............................................................... 20
Main categories of fence explained .............................................................................................. 20
Barrier Fences ............................................................................................................................... 21
Electric fences ............................................................................................................................... 22
Combination fences ...................................................................................................................... 24
Fence specifications ...................................................................................................................... 25
Chapter 3. Planning and installing an anti-predator fence, including Health and Safety requirements
and cost ......................................................................................................................................... 26
2
Introduction .................................................................................................................................. 26
Key considerations when deciding whether to install a fence ..................................................... 26
Electric Fence Health and Safety requirements ............................................................................ 26
Fence design ................................................................................................................................. 28
Fence Cost ..................................................................................................................................... 28
Fence construction ........................................................................................................................ 29
Vandalism ...................................................................................................................................... 30
Chapter 4. Barrier Fences, their use, design and specification ............................................................. 31
Barrier fence design and siting principles ..................................................................................... 31
Standard configurations ................................................................................................................ 32
Barrier fencing specifically against badgers .................................................................................. 33
Australian barrier fence designs against foxes and cats ............................................................... 34
Barrier fences in water .................................................................................................................. 37
Chapter 5. Combination Fences, their use, design and specification ................................................... 41
Use ................................................................................................................................................ 41
Design principles ........................................................................................................................... 41
The electric fence component ...................................................................................................... 42
The recommended standard configuration .................................................................................. 42
Factors to consider when deciding the route of the fence ........................................................... 46
Cost of combination fencing ......................................................................................................... 49
Fence operation ............................................................................................................................ 49
Chapter 6. Permanent/semi-permanent electric strand fences .......................................................... 50
Use ................................................................................................................................................ 50
Siting.............................................................................................................................................. 50
Design principles ........................................................................................................................... 51
Principles of effective fence design .............................................................................................. 51
Strand Fence specifications .......................................................................................................... 53
Variation from the standard configuration. .................................................................................. 55
Installation .................................................................................................................................... 56
Operation ...................................................................................................................................... 57
Maintenance ................................................................................................................................. 58
Monitoring .................................................................................................................................... 58
Effectiveness of electric strand fences at excluding predators .................................................... 60
Chapter 7. Temporary electric fences ................................................................................................... 61
3
Situations where the use of temporary electric fences is appropriate ........................................ 61
Siting.............................................................................................................................................. 62
Types of temporary/portable electric fences ............................................................................... 62
Temporary strand fences ...................................................................................................................... 62
Specification .................................................................................................................................. 62
Installation .................................................................................................................................... 63
Operation ...................................................................................................................................... 65
Maintenance ................................................................................................................................. 65
Monitoring .................................................................................................................................... 65
Effectiveness ................................................................................................................................. 66
Problems encountered with the Minsmere fences ...................................................................... 66
Berney Marshes case study (Jim Rowe and Mark Smart) ............................................................. 66
Brading Marshes Case Study (Keith Ballard) ................................................................................. 67
Other temporary electric strand fence configurations ................................................................. 68
Case studies .................................................................................................................................. 70
Electrified mesh netting ........................................................................................................................ 72
Case studies .................................................................................................................................. 74
Chapter 8. Key Electric Fence Components ......................................................................................... 76
Some definitions ................................................................................................................................... 76
Choosing and installing components with the appropriate specification ............................................ 76
Energisers .............................................................................................................................................. 76
Description .................................................................................................................................... 76
Power supply ................................................................................................................................. 77
Choosing the correct energiser ..................................................................................................... 77
Case studies .......................................................................................................................................... 82
Rainham ........................................................................................................................................ 82
Cattawade ..................................................................................................................................... 82
Greylake ........................................................................................................................................ 82
North Kent ..................................................................................................................................... 83
Rye Harbour .................................................................................................................................. 83
Minsmere ...................................................................................................................................... 83
Malltraeth(Tai Hirion) ................................................................................................................... 83
Earthing (ground) system) .................................................................................................................... 84
The number of earthing posts or stakes (ground rods) ................................................................ 85
4
Where to site the earth system .................................................................................................... 86
Testing the earth system............................................................................................................... 87
Cut-off switches .................................................................................................................................... 88
Insulators .............................................................................................................................................. 88
Insulated Cable...................................................................................................................................... 89
Posts ...................................................................................................................................................... 89
Choice of material ......................................................................................................................... 89
Desired service life ........................................................................................................................ 89
Choice of wood ............................................................................................................................. 90
Treatment ..................................................................................................................................... 90
Additional treatment to prolong fence post life ........................................................................... 91
Aftercare ....................................................................................................................................... 92
Post dimensions ............................................................................................................................ 92
Chapter 9. Reducing the challenge to predator exclusion fences ........................................................ 94
Fence design ................................................................................................................................. 94
Reducing predator ‘pressure’ ....................................................................................................... 97
When should predator fences be operational? ............................................................................ 98
Chapter 10. Fence monitoring and maintenance .............................................................................. 100
Monitoring .................................................................................................................................. 100
Fence maintenance ..................................................................................................................... 102
Common fence maintenance problems requiring remediation ................................................. 103
Detecting the presence of foxes inside an anti-predator fence ................................................. 105
Chapter 11. Effects of anti-predator fences on non-target species .................................................. 106
Badger gates ............................................................................................................................... 107
References .......................................................................................................................................... 108
Acknowledgements ............................................................................................................................. 109
APPENDIX 1. Appropriate fence types for different species for which anti-predator fences can
increase nesting success or productivity .................................................................................... 110
Wet grassland breeding waders ................................................................................................. 110
Soft shore seabirds ...................................................................................................................... 110
Avocets and other waders breeding at coastal lagoons ............................................................. 110
Stone-curlews and individual nests/pairs of other rare ground nesters .................................... 111
APPENDIX 2. The evidence base for fence design against specific predator species ........................ 112
Foxes ........................................................................................................................................... 112
5
Badgers ....................................................................................................................................... 115
Cats .............................................................................................................................................. 116
Hedgehogs .................................................................................................................................. 117
Otters .......................................................................................................................................... 117
APPENDIX 3. How Electric Fences Work (http://www.Rappa.co.uk) ................................................ 118
APPENDIX 4. Major fence manufacturers, stockists & contractors ................................................... 121
APPENDIX 5. RSPB reserves employing an anti-predator fence(s) up to 2017. ................................. 122
APPENDIX 6. UK case studies of barrier fences ................................................................................. 125
Fences in perimeter ditches ........................................................................................................ 125
Barrier fences around islands (Rye Harbour) .............................................................................. 132
Barrier fences on land ................................................................................................................. 137
APPENDIX 7. UK case studies of combination fences ......................................................................... 140
Rye Harbour ................................................................................................................................ 140
Rainham Marsh ........................................................................................................................... 143
Great Bells Farm, Kent ................................................................................................................ 150
APPENDIX 8. Detecting the presence of foxes and badgers inside an anti-predator fence. ............. 155
Tracking plots .............................................................................................................................. 155
Thermal imagers ......................................................................................................................... 155
Trail Cameras .............................................................................................................................. 156
APPENDIX 9. Box Strainers ................................................................................................................. 159
Construction of Box Strainers ..................................................................................................... 160
Box struts .................................................................................................................................... 160
6
How to use this guide
To avoid the need to repeat the same information on different pages, hyperlinks (indicated by blue text) are provided throughout the text to give quick access to information in another part of the document.
The guide is based on the premise that site managers should have an understanding of the principles
of predator exclusion fences to enable for them to make the right choice of fence design and
specification for their particular situation and the monitoring and maintenance needed to maintain a
fence’s effectiveness. To get the most out of the guide:
1. Read the general introduction (Chapter 1). If you are still interested in installing a fence having read this:
2. Decide whether to install a fence and what type of fence to install. (Chapter 2).
3. Start the planning process by considering where to site the fence, rough cost, Health and Safety requirements and other considerations (Chapter 3).
4. Finalise the fence design by reading the chapter appropriate to the type of fence you want to install (Chapters 3-6). Decide whether the standard recommended design for each category of fence is sufficient for your situation or whether you might need to stray from this by referring to the case studies in individual chapters or those in the Appendices.
5. Decide what ancillary fence materials and components you will need and their specification e.g. posts, energisers (Chapter 7).
6. Consider how the fence will be operated, including reducing the predator challenge to the fence, the required monitoring and maintenance regimes and the potential effects of the fence on non-target species (Chapter 8).
Checklist of important actions before installing and operating an anti-
predator fence
• Ensure the fence complies with Health and Safety requirements.
• Show the fence spec to your Rural Surveyor and Ecologist.
• Obtain specific NE consent if installing a fence on a SSSI and if undertaking an operation needed for fence installation, if these were not previously agreed in the management plan e.g. ditch widening, constructing a new bund to carry the fence.
• Obtain derogations from the relevant Statutory Agencies as necessary e.g. you cannot spray within 2m of a water course without derogation from EA (cross-compliance issue).
• Obtain a disturbance licence(s) from the relevant Statutory Agency as necessary.
• Inform your Regional land agent re-compliance if the fence results in a change to the area grazed.
• Inform your Rural Surveyor if a fence will remain in place for >3 years. If so, this will require a change to the RPA map to show the position of the new boundary.
7
Chapter 1. General introduction Where practicable, RSPB policy is to use predator exclusion fences to try to raise the productivity
of ground nesting birds to an appropriate level in order to reduce the need for the lethal predator
control. Experience from RSPB reserves suggests that predator exclusion fences can be very
effective at reducing predation by large, generalist mammalian predators, if they are specified,
installed and maintained correctly.
What are we trying to achieve by the use of predator exclusion fences on reserves?
Fencing alone will not provide a complete solution to predator problems on reserves. It is generally
accepted that no fence will be totally effective indefinitely, especially against foxes. Trying to reduce
predation is an ‘arms race’; foxes under trial conditions have been found to quickly learn how to
overcome various arrangements of electric wires. Fortunately, creating an area that is 100% free
from predation is both unrealistic and unnecessary. As a minimum we are seeking to ensure that
the level of productivity of the target species is above that needed to maintain the population i.e.
the reserve should not be a population sink for the target species. However, the general aim is to
manage our reserves so that populations of their key species are sufficiently productive to expand
into the surrounding countryside i.e. reserves should be potential sources of colonisation.
Is predation a problem?
It is now widely accepted that in certain situations in the UK predation by generalist mammalian
predators (principally foxes and badgers) can reduce productivity of ground-nesting birds to below
that needed to maintain their populations. It seems to be a particular problem on nature reserves,
where vulnerable species are often nesting at higher densities than in the surrounding countryside,
often making them particularly liable to high rates of predation.
Why use predator exclusion fences?
Most nature conservation organisations, including RSPB, prefer to use non-lethal methods to reduce
the impact of predators where this is practical and effective, and this is the only option for badgers.
Also, even though lethal control of foxes by shooting is allowed on RSPB reserves in some
circumstances, it is challenging to reduce the impact of fox predation to the level required by this
means alone. Currently, the only non-lethal option consistently shown to increase the productivity
of vulnerable ground nesting birds is predator-exclusion fencing (Smith et al. 2010; Malpas et al.
2013), which seeks to deny or reduce access by large ground predators to the area where the birds
are breeding (either dispersed nests or breeding colonies). Other non-lethal means of reducing
predation such as habitat manipulation, diversionary feeding and aversive conditioning may be
applicable in particular situations, but none has yet been shown to be effective generally.
To install a fence or not?
It is only worth installing anti-predator fencing at sites where appropriate and effective habitat
management is in place, the target species breeds in significant numbers but productivity is low (i.e.
below maintenance level) due to predation from large ground predators. Additionally, a fence may
be justified if there is the potential for the target species to breed in significant numbers, but there is
evidence that the population is being suppressed by predators preventing birds from settling or
depressing productivity below that required to maintain the population.
8
Main target species to benefit from anti-predator fences
Most fences in the UK have been installed to increase the nest success/productivity of either:
- breeding waders of wet grassland (especially lapwing) to above maintenance level
- breeding waders nesting at high density on machair
- colonially nesting soft-shore seabirds on shingle banks or islands in coastal lagoons
- avocets nesting at high density at coastal lagoons
- stone curlews breeding on heathland or nesting plots in grassland/arable
- isolated nests of rare or threatened species e.g. Montagu’s harrier, black-winged stilt.
Predator-exclusion fencing deters large mammalian predators in two ways: either by presenting a
physical barrier and/or by modifying behaviour through the use of an unpleasant electric shock
(Poole & McKillop 2002). Most fences on reserves are intended to exclude/deter foxes and/or
badgers. Some fence designs are also effective against cats, hedgehogs and otters.
Do predator exclusion fences work? Fences work if they are well-sited, well-designed and well-maintained. They work alongside
effective habitat management, not as a substitute for it, and should only be considered when
predators are likely to limit the productivity of the target species.
Different designs of anti-predator fencing have been trialled at RSPB reserves since 2003. The fences
are designed to exclude foxes and badgers but not small mustelids e.g. stoats. All the evidence
suggests that fences that have been correctly designed, installed and maintained will be sufficiently
successful at excluding foxes and badgers to lead to an increase in the breeding success of the target
species.
The effectiveness of fences in increasing nesting success Fencing is generally very successful at excluding foxes and badgers. Lapwing hatching success
almost doubles within predator fencing and this is true for inside-outside and before-after
comparisons (Fig. 1). Survival of lapwing nests within fenced areas across reserves has been on
average 78%. This is much higher than the estimated 45-50% nest survival thought to be required to
maintain a stable population of lapwings.
Fig 1. Lapwing hatching success on reserves inside and outside anti-predator fences and before and
after fences were installed. The line indicates the 50% nest survival needed to maintain a
stable population.
9
This high level of nest survival has been achieved in spite of fencing only being used where lapwings
have experienced consistently low nest survival and overall breeding productivity.
There is less information on the effects of anti-predator fences on the nest survival of other breeding
waders of wet grassland such as redshank and snipe, but there is increasing evidence that they
benefit these species too. On the Nene Washes in 2015-2017 daily nest survival rates of three
species of wader combined (lapwing, redshank and black-tailed godwit) were significantly (2.3x)
higher in two fenced areas than an equivalent area with no exclusion of ground predators (Fig. 2).
71% of nest predations recorded occurred at night and were assumed to be mammalian.
Fig. 2. Daily predation rate of nests of all wader species in relation to different predation
management treatments. Nests in areas fenced against predators (Fence+gates) experienced
significantly lower predation.
Effect of fences on lapwing productivity On average lapwing productivity is over 2.5x higher after an anti-predator fence is installed (Fig. 3)
on a reserve (1.0 vs 0.39 fledged chicks per pair).
Fig. 3. Mean annual lapwing productivity (+ 2 SE) at 20 sites before and after fence installation.
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
No exclusion Gates Fence+gates
Dai
ly p
red
atio
n r
ate
±9
5%
CI
0
0.2
0.4
0.6
0.8
1
1.2
1.4
Pro
du
ctiv
ity
(fle
dge
d c
hic
ks/p
air)
Before fenceAfter fence
10
It was feared that any benefits of increased lapwing nest survival within areas protected by anti-
predator fences might be offset by high levels of chick predation by avian predators hunting inside
the fence or from low nesting success outside the fenced area. However, generally this does not
seem to be the case, except at one wet grassland reserve (Otmoor, see below). Estimated levels of
lapwing chick survival at sites with fences are consistently higher than the 0.6 chicks fledged per pair
considered necessary to maintain a stable population (Fig. 4).
Fig. 4. Mean lapwing productivity (+ 2SE) at RSPB reserves with and without anti-predator fencing at
which productivity has been monitored regularly. The dotted line indicates the estimated
level of productivity (0.6 fledged chicks/pair) required to maintain a stable lapwing
population.
In over 70% of ‘site-years’ after fence installation lapwing productivity has been more than that
considered necessary to maintain a stable population (Table 1).
Table 1. Percentage of ‘site years’ that productivity was above 0.6 fledged chicks per pair before and
after fence installation. Figures in parentheses are the number of site-years in each
category.
% Years< 0.6 % Years > 0.6
Before fence 76.4 (42) 23.6 (13)
After fence 28.9 (37) 71.1 (91)
Note that overall lapwing productivity across the whole of the sites in Figure 3 was above that
needed to maintain a stable population even though anti-predator fences usually only protect a
proportion of the reserve’s wet grassland area (6–100%) i.e. not all the site to needs to be fenced to
achieve the desired level of productivity of the target species. In part this is because the densities of
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2010 2011 2012 2013 2014 2015 2016 2017 2018Lap
win
g p
rod
uct
ivit
y (f
led
ged
ch
icks
/pai
r)
Fenced sites
Unfenced sites
11
wet grassland waders nesting within predator exclusion fences are often higher than in the
‘unprotected’ parts of the reserve. This has two effects – a disproportionate number of the target
species is protected by the fence and those birds that nest outside are at lower density reducing
their chances of being predated and so some are likely to breed successfully.
Effects of avian predation on lapwing productivity within fenced areas Anti-predator fences are effective only against ground predators such as foxes, cats, badgers and
hedgehogs. Birds can also be important predators of some target species and fencing will not
reduce the impact of avian predation and could potentially serve to increase it by concentrating
nests or chicks within a small area making them more vulnerable to avian predation. Nevertheless,
at most reserves the effects of reducing predation on nests and chicks from ground predators is not
then outweighed by higher levels of avian predation (see above).
Although lapwing productivity at sites with fences is generally above the level needed for a stable
population (Fig. 3), there is always the potential for avian predators to start to concentrate on wader
chicks at some sites, particularly in years when alternative prey is less abundant. One example is the
particularly heavy predation by red kites of lapwing chicks within the fenced area in some years at
Otmoor, where a high proportion of the reserve’s lapwings breed at high density inside the 42ha
fence. In 2012 and 2013 kite predation reduced lapwing productivity to below the 0.6 fledged chicks
per pair needed for population maintenance (Fig. 5). Experimental diversionary feeding of red kites
in two subsequent years allowed lapwing productivity to increase to acceptable levels suggesting
that the fence was still effective against predation by foxes and badgers (Fig. 5).
Fig. 5. Lapwing productivity at Otmoor RSPB Reserve in relation to fence installation (dotted line)
and red kite predation on lapwing chicks. The thick horizontal line is the level of productivity
needed for population maintenance. The red data points indicate years when diversionary
feeding of kites was undertaken.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
Fled
ged
lap
win
g ch
icks
/pai
r
No fence Fence
Kite predation
Div. Feeding
12
Fig. 5. Lapwing productivity at Otmoor RSPB Reserve before and after fence installation (dotted line).
The thick horizontal line is the level of productivity needed for population maintenance. Red
kites began predating lapwing chicks in 2012. Diversionary feeding (DF) of kites was
undertaken in 2015 and 2016.
Do birds prefer to nest inside predator fences?
There is increasing evidence that lapwings settle preferentially in areas from which foxes and
badgers have been excluded, presumably because birds settling are not being continually disturbed
by these potential predators and, therefore, ‘feel safer’. At Otmoor RSPB Reserve, the first season
after the fence was erected many lapwings laid their first clutches outside of the fenced area, but
then re-laid replacement clutches within the fenced area after their first clutches were predated.
The following year a higher proportion of lapwings laid their first clutches within the fenced area.
Now most lapwings nest inside the 42ha combination predator fence where their hatching success is
much higher (Fig. 6).
Fig. 6. The influence of nest location on the hatching success of lapwing nests at Otmoor
DF
DF
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
Fle
dge
d c
hic
ks/p
air
Red kite predation
0
20
40
60
80
100
2013 2014 2015
Pe
rce
nt
ne
sts
hat
che
d
Inside fence
Outside fence
13
At Hollesley in 2014, the breeding densities of lapwing and redshank within the new predator
exclusion fence were much higher than found generally at wet grassland reserves and all species
exhibited high productivity (Table 2).
Table 2. The densities and productivity of wetland birds breeding within the newly fenced area
(18ha) at the Hollesley section of Boyton Marshes in 2014
Species No. pairs Density prs/ha Productivity (chicks/pair)
Shelduck 1 7
Shoveler 1 7
Avocet 41 2
Oystercatcher 1 2
Ringed plover 3 3
Lapwing 25 1.4 2.4
Redshank 10 0.6 3
A 6.9km long combination fence enclosing 64ha (split into three separate sections) was installed at
Rye Harbour Nature Reserve in 2003 to protect breeding terns, waders (ringed plover, redshank and
lapwing) from foxes, badgers, dogs and people. All of the first nesting attempts of lapwing were
inside the fence, despite suitable habitat outside. Numbers of nesting Sandwich terns and black-
headed have doubled since the fence was installed and many pairs have nested successfully on the
“mainland”, rather than just on islands as they did previously.
If productivity at a site is maintained above maintenance levels do numbers of breeding lapwing increase? As a minimum we are seeking to ensure that the level of productivity of a target species is above
that needed to maintain the population i.e. the reserve should not be a population sink for the
target species. However, the general aim is to manage reserves so that the population of the target
species increases and then becomes capable of colonising suitable habitat in the surrounding
countryside.
Data on lapwing numbers and productivity for the period 2012-2018 was available for 20 reserves
with >20 pairs of lapwing present at either the beginning or end of the time series. Sites with fewer
lapwing were omitted from the analysis. The correlation between the rate of population increase
and the mean level of productivity (Fig. 7) is not significant but suggests that if lapwing productivity
on a reserve is consistently above the level needed for population maintenance then lapwing
numbers are likely to increase. If the two most extreme outliers are omitted (Ynys-hir -higher than
expected mean productivity and the Dee - lower than expected mean productivity), the correlation
becomes significant (R2= 0.541; P=<0.05).
14
Fig. 7. The trend in numbers of breeding lapwing (slope of linear regression) from 2012-2018 in
relation to mean lapwing productivity at 20 sites with >20 pairs of lapwing. The two furthest
outliers are Ynys-hir (higher than expected mean productivity) and the Dee (lower than
expected productivity). If these are omitted R2= 0.541.
At three reserves the increase in lapwing numbers following fence installation has been spectacular
(Fig. 8). At all three reserves mean productivity has been well above the 0.6 chicks per pair needed
for population maintenance (Dee 0.84, Rainham 0.93 and Cors Ddyga 1.56).
Fig. 8. Trends in the number of breeding lapwing following fence installation at three reserves.
R² = 0.3328
-6
-4
-2
0
2
4
6
8
10
12
14
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80
Tre
nd
in la
pw
ing
nu
mb
ers
(sl
op
e o
f re
gre
ssio
n)
Mean lapwing productivity
0
20
40
60
80
100
120
2012 2013 2014 2015 2016 2017 2018
Bre
ed
ing
pai
rs o
f la
pw
ing
Year
Dee
Rainham
Cors Ddyga
15
At some reserves there may be the potential for the target species to breed in significant numbers
e.g. an extensive area of habitat appears suitable, but mammalian predators may be preventing
birds from settling and/or depressing productivity below that required for population maintenance.
Where there is evidence that this is the case, installing a fence may be justified. At Malltraeth (Cors
Ddyga) RSPB reserve, the target number of breeding lapwings when the reserve was acquired in
1994 was 30 pairs, but numbers remained at around 10 pairs in spite of the habitat being in suitable
condition and capable of supporting much larger numbers. Fox control began in early 2011 and the
main areas of lapwing habitat were fenced against foxes and badgers prior to the 2012 breeding
season. Since then productivity has been above the 0.6 chicks/pairs needed for population
maintenance and lapwing numbers have continued to increase to more than double the original
target (Fig. 9).
Fig. 9. Lapwing productivity and numbers at Cors Ddyga (Malltraeth) before and after fence
installation (vertical dotted line). Ground predators were keeping lapwing numbers and
productivity below the site’s potential.
How effective are anti-predator fences compared with other predation management options? Since 2012 mean lapwing productivity has been well above the level needed for population
maintenance (0.6 fledged chicks per pair) in every year at reserves with an anti-predator fence and
consistently higher than at reserves where there is fox control only (Fig. 10). At reserves with fox
control but no anti-predator fence, mean lapwing productivity was lower than at sites with fences
but still above the population maintenance level in all but one year. By contrast, at reserves with no
form of predator management mean lapwing productivity was above maintenance level in only one
year.
0
0.5
1
1.5
2
2.5
3
3.5
4
0
10
20
30
40
50
60
70
80
2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018Fl
edge
d c
hic
ks p
er p
air
Nu
mb
er o
f p
airs
Year
Pairs
Fledged chicks/pair
Productivity needed forpopulation maintenance
16
Fig. 10. Annual mean lapwing productivity (+ 1SE) at reserves with different predation management.
Overall, mean lapwing productivity is well above population maintenance level (0.6 chicks per pair)
at sites with fences (Fig. 11) and significantly higher than at sites with fox control but no fence.
However, at these sites (fox control but no fence), mean lapwing productivity is significantly higher
than reserves with neither a fence nor fox control, where on average productivity is well below
maintenance level.
Fig. 11. Mean lapwing productivity at sites with different predation management.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
2012 2013 2014 2015 2016 2017 2018
Lap
win
g p
rod
uct
ivit
y (c
hic
ks/p
air)
Year
All sites with a fence
Fox control only
No predation management
0
0.2
0.4
0.6
0.8
1
1.2
All fenced sites Fox control only No predationmanagement
Pro
du
ctiv
ity
(fle
dge
d c
hic
ks/p
air)
17
Potentially, the ‘belt and braces’ approach of controlling foxes on reserves with an anti-predator
fence(s) could lead to even higher lapwing productivity by increasing nest and fledging success
outside the fence and by reducing fox incursions into the fenced area. However, there is no clear
difference in lapwing productivity between reserves with a fence only and sites with both a fence
and fox control (Fig. 12).
Fig. 12. Mean annual lapwing productivity (+ 2 S.E.) at reserves with different predator management
Potential decline in fence performance over time
When all sites and all types of fence are considered, there appears to be a negative trend between
lapwing productivity and fence age, beginning after Year 5 (Fig. 13.). However, note that even after
this, productivity is still around the level needed for population maintenance.
0
0.2
0.4
0.6
0.8
1
1.2
Lap
win
g p
rod
uct
ivit
y (f
led
ged
ch
icks
/pai
r)
Fence only
Fence + fox control
Fox control only
No predation management
18
Fig. 13. Mean lapwing productivity (+2SE) in relation to the time since the anti-predator fence was
installed. The horizontal line indicates the level of productivity needed for population
maintenance. The number of reserves is shown above the error bar.
Several different factors could be contributing to the relationship in Fig. 13:
• Fence specification has improved over time (most of the first fences installed were strand
fences).
• Fence condition declines over time due to lack of maintenance and ground predators
penetrate fence
• Ground predators learn to penetrate fence.
• Predators not excluded by the fence e.g. raptors discover the increasing prey resource.
Chick predation seems to become more of a problem after the first couple of successful
years post fencing.
• Habitat quality declines inside the fence.
21
21
1915
13
11
7
6 5
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1 2 3 4 5 6 7 8 9
Lap
win
g p
rod
uct
ivit
y (
chic
ks/p
air)
Years since fence installed
19
Chapter 2. Deciding whether to install a fence and the fence type
What are we trying to achieve by the use of anti-predator fences on reserves? Fencing alone will not provide a complete solution to predator problems on reserves. It is generally
accepted that no fence will be totally effective indefinitely, especially against foxes. Trying to
reduce predation is an ‘arms race’; foxes under trial conditions have been found to quickly learn how
to overcome various arrangements of electric wires. Fortunately, creating an area that is 100% free
from predation is both unrealistic and unnecessary. As a minimum we are seeking to ensure that
the level of productivity of the target species is above that needed to maintain the population i.e.
the reserve should not be a population sink for the target species. However, the general aim is to
manage our reserves so that populations of their key species are sufficiently productive to expand
into the surrounding countryside i.e. reserves should be potential sources of colonisation.
To install a fence or not? It is only worth installing anti-predator fencing at sites where appropriate and effective habitat
management is in place, the target species breeds in significant numbers but productivity is low (i.e.
below maintenance level) due to predation from large ground predators. Additionally, a fence may
Fig. 4a. Lapwing productivity and numbers at Malltraeth before and after fence installation (dotted line). Ground predators were keeping lapwing productivity and numbers below potential.
0
0.5
1
1.5
2
2.5
3
20
09
20
10
20
11
20
12
20
13
20
14
20
15
20
16
20
17
Ch
icks
fle
dge
d p
er p
air
Lapwing productivity
0
10
20
30
40
50
60
70
80
20
03
20
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17
Nu
mb
er
of
pai
rs
Lapwing numbers
20
be justified if there is the potential for the target species to breed in significant numbers, but there is
evidence that the population is being suppressed by predators preventing birds from settling or
depressing productivity below that required to maintain the population. At Malltraeth (Cors Ddyga)
RSPB reserve, the target number of breeding lapwings when the reserve was acquired in 1994 was
30 pairs, but numbers remained at around 10 pairs in spite of the habitat being in suitable condition
and capable of supporting much larger numbers. Fox control began in early 2011 and the main areas
of lapwing habitat were fenced against foxes and badgers prior to the 2012 breeding season. Since
then productivity has been above the 0.6 chicks/pairs needed for population maintenance and
lapwing numbers have continued to increase to more than double the original target (Fig. 4a).
Anti-predator fences are effective only against ground predators such as foxes, cats, badgers and
hedgehogs. Birds can also be important predators of some target species, but fencing will not
reduce the impact of avian predation and might even serve to increase it (see earlier).
Main target species to benefit Most fences in the UK have been installed to increase the nest success/productivity of either:
- breeding waders of wet grassland (especially lapwing) to above maintenance level
- breeding waders nesting at high density on machair
- colonially nesting soft-shore seabirds on shingle banks or islands in coastal lagoons
- avocets nesting at high density at coastal lagoons
- stone curlews breeding on heathland or nesting plots in grassland/arable
- isolated nests of rare or threatened species e.g. Montagu’s harrier, black-winged stilt.
The species and situations in which anti-predator fences have been successful at increasing nesting
success and/or productivity are described in detail in Appendix 1.
Fence design appropriate for specific predator species The evidence base for fence design against specific predators (foxes, badgers, cats, otters and
hedgehogs) is given in Appendix 2. This provides a useful insight into the fence specification needed
to exclude each of these potential predators and should help inform the eventual design.
Main categories of fence explained There are two basic types of anti-predator fence: barrier and electrified, which can also be used in
combination. In some cases the fences serve a dual purpose of retaining stock and excluding
predators.
Fences can either be permanent (remain in the same place for 10+ years), semi-permanent (remain
in same place but with a life-span of <10 years) or temporary (installed afresh each year). Obviously,
temporary fences can be moved to different locations between years.
Type of fence Permanent Semi-permanent Temporary
Barrier Yes (Yes)1 (Yes)2
Electrified No Yes Yes
Combination Yes No No 1Specialised type of barrier fence specifically against hedgehogs. 2Mobile barrier fence placed around harrier nests.
21
Barrier Fences These provide a physical barrier which the target predator cannot cross. They are made of either
high tensile wire used to create a rigid netting framework or, more commonly, mesh wire supported
on metal or sometimes wooden posts. In the UK they are usually intended to exclude foxes and
sometimes badgers, otters or hedgehogs. The mesh or gaps between the wires must be small
enough to exclude the target species (e.g. 70-80mm for an adult fox).
In the UK, barrier fences are most often placed in water wide enough to make it impossible for the
target predator to jump over and to burrow under and more difficult to climb (e.g. a wide ditch
around a block of wet grassland or around an island in a water body). In terrestrial situations, to be
fox proof requires a fence that is 1.8-2m high with an outward facing overhang at the top and an
outward facing horizontal apron (usually wire mesh and often buried) to prevent animals burrowing
under the fence.
Specific advantages:
• Siting: Can be installed on land or in water
• Durability and lifespan: 30+ years high-tensile, 15-20 years for mesh wire (if not installed in
water). Not known for fences installed in water, but saline conditions especially could cause
rapid corrosion of wire products.
• Maintenance: easier to maintain than fences which rely wholly or in part on electricity for
their effectiveness. Damaged areas are easy to locate (unless below water).
• Utility: the same design can be effective against foxes, badgers, cats and hedgehogs.
Disadvantages:
• High material cost: Unless installed in water, the most expensive fence per unit length due to the high cost/quantities of the materials required.
• High installation cost: more difficult and time consuming to install than electric strand
fencing.
• Height: Unless installed in water, usually needs to be taller than an electric fence
(combination fences intermediate).
• Visually intrusive: their height and close mesh means that they have a higher visual impact
than electric strand fences.
• Complexity: Unless in installed in water, an apron (horizontal section of fence on the ground
surface or buried) is needed to prevent animals burrowing under and an overhang is needed
to stop foxes jumping or climbing the fence.
• Effectiveness: They can be climbed, particularly at weak points such as corners and
gateways. The posts supporting the fence can provide perches for avian predators such as
crows and buzzards.
• Effect on other species: The small maximum mesh size (70 - 80mm or less) of the fence can
restrict local movements of non-target species such as hares
• Maintenance: mesh wire sags over time
Main uses Conventional barrier fences should only be considered at sites where fencing is required in the same
location every year as they are expensive and difficult and time-consuming to install. To be
effective, design, construction and maintenance need to be meticulous. However, once installed,
22
less vegetation control is required than for stranded electric or combination fences, there are no
electric wires to fail and the fences are more rigid and so less prone to damage. They have a longer
lifespan than a conventional nine+ strand electrified fence (although possibly not if installed in
water) and are also friendlier to wader chicks and hedgehogs. Furthermore, the same design can be
effective against foxes, badgers, cats and hedgehogs and as they do not rely on electricity to exclude
predators, they can be installed in water. However, unless installed in water, to be effective against
foxes they generally need to be taller than an equivalent electric fence (combination fences are
intermediate) and their height and relatively close mesh means that they have a higher visual impact
than electric strand fences and some combination fences. However, they can also serve as a stock
fence, especially if a single strand of barbed wire is run around the inside to stop stock rubbing
against it.
In the UK, the principal use of barrier fences has been to try to exclude foxes and badgers from
accessing islands within shallow water bodies holding colonially nesting gulls or terns. Recently,
barrier fences have been used to protect much larger areas from incursions by foxes or badgers by
installing them in water-filled perimeter ditches or in one case around a whole waterbody (Upton
Warren).
More specialist versions of barrier fences have been used to protect the nests of waders breeding on
machair in the Outer Hebrides from predation by hedgehogs (see here) and low (1.2m high) barrier
fences are used around Montagu’s harrier nests to prevent foxes predating the chicks (see here).
Electric fences These work by the combination of a weak physical barrier (the fence) and a strong psychological
imprint to modify the behaviour of the predator (the animal associates the shock with the fence to
create a psychological barrier that discourages it from touching it again). Mains electricity or a
battery powered energizer attached to the wires produces a short but unpleasant shock (c.4-6000v)
when the wire is touched. The low amperage (15-100mA) and short duration (about 1/300th. of a
second) results in a sharp but safe sting.
An electric fence system comprises six components (See Appendix 3 for how electric fences work):
1. A battery or mains powered energiser produces a pulsed electric current along the fence wires.
2. An earthing rod driven into the ground returns the electrical pulse of energy to the energiser.
3. Wood, metal, plastic or fibreglass stakes to support the fence.
4. Insulators attached to the fence stakes to ensure the pulsed current is not lost to earth but
maintained to provide a sharp, high voltage shock (4KV or above) to any animal touching a live wire.
5. Single or multi-strand steel wires to conduct the current. Electrified plastic netting can be used
against foxes, but hedgehogs may get entangled as they react to a shock.
6. A proprietary fence tester to check whether the fence is providing sufficient voltage. Reliance on
grass stems or twigs provides only a crude indicator of whether the fence is working!
The key fence components are discussed in more detail later.
Electrified fences can be either semi-permanent or temporary/portable.
23
Semi-permanent electric fences Strained wire fences comprise a series of electrified parallel conducting (i.e. live) usually steel
(galvanized plain or strand) wires alternating with non-electrified earth wires at varying heights
above the ground and supported at intervals by posts.
Advantages
• Cheap: less expensive than barrier and combination fences.
• Visual impact: low
• Height: lower than barrier fences
• Safe: a 1.5J (low) energy capacity fence is sufficient to exclude foxes because of their small
body size (McKillop et al., 1999)
• Simple: the addition of an extra earthed wire at the bottom can prevent animals digging
underneath (McKillop et al., 1999)
• Flexibility: wires can be turned off independently (McKillop et al., 1999) e.g. the lowest live
wire could be turned off once nidifugous chicks have hatched.
Disadvantages
• Effectiveness against target species: the most effective strand configurations against foxes
and badgers probably differ.
• Electricity supply: Effectiveness mainly dependent on the reliability of the electricity supply.
Mains supply is more reliable and effective (Malpas et al. 2012). If there is no mains supply,
batteries can be used, but these will need recharging at least every two weeks (McKillop et
al., 1999) unless supplementary power supplied e.g. from a solar panel.
• Reliability: Earthing may be a problem on dry sites. If vegetation comes into contact with
the live wires, charge is lost and battery power drains away quickly. If the fence fails, it is
only a weak barrier to animal movement, although equipment that detects loss of voltage
can be used to set off an alarm in the event of fence failure.
• High maintenance: To prevent shorting on vegetation requires additional maintenance such
as mowing, grazing, herbicides etc. Tension needs to be kept in wires, so regular
maintenance visits are essential.
• Durability: effective lifespan is less than for a barrier or combination fence (although can last
up to 10 years if properly built and maintained).
• Effect on other species: Hedgehogs and frogs, and in one case a lapwing chick, have been
killed by the bottom live wire.
• Installation: Hard to install on uneven terrain. For people or vehicles to cross requires the
use of electrified gates, which can be expensive. Non-electrified gates are vulnerable to
breaching by foxes.
Temporary/portable electric fences
Usually these are either:
Wire strand fences comprising a series of electrified parallel conducting wires at varying heights above
the ground usually made from Polywire (polythene twine interwoven with steel strands). Polywire is
cheaper but is a poorer conductor than galvanised steel wire. Because of the ease of installation,
most temporary fences utilise polywire rather than steel wires. Polywire strands can be wound onto
24
reels for easy transport and can be supported by lightweight plastic polystakes (rather than wooden
posts).
or:
Electrified netting fences. These consist of a heavy-duty, polythene twine mesh in which the horizontal
strands are interwoven with electrically conductive stainless steel wire supported by vertical strands
of plain polythene twine. Fences vary in height and mesh size, depending on the manufacturer, and
come in 25 or 50m rolls fitted with spiked plastic or fibreglass supporting posts built into the fencing
at regular intervals (c.3m) with a clip at each end to join rolls together. These fences are very easy
and quick to erect and dismantle.
The strained-wire design offers advantages over netting in terms of durability and versatility. It also
carries a higher voltage than netting and can be less damaging to other wildlife, such as hedgehogs
and amphibians which can become entangled within mesh and killed as a consequence.
Advantages
• Ease of installation: Quick and simple to assemble and take down.
Posts used can be less strong and fences less rigid because they will not be out all year round
in bad weather (McKillop et al., 1999)
• Flexibility: Straightforward to alter the perimeter and the area incorporated.
• Effectiveness: usually only have to exclude target predators for a comparatively short period
of time to be worthwhile (e.g. 6-8 weeks for wet grassland breeding waders).
Disadvantages
• Low durability: The framework is less rigid, therefore wires are more likely to sag or get
damaged, particularly if there are livestock.
• Lifespan: Materials used are usually lower quality, so they have a shorter lifespan
• Visual impact: can be high, if the stakes, wire or netting are made of brightly coloured
materials
• Effectiveness: Netting cannot carry as high a voltage as stranded wire (Poole & McKillop,
2002) and is only suitable for small areas (Rappa Fencing Ltd).
• Effect on other species: Potential risk of wader chicks coming into contact with the
electrified wires of a net fence. (Although, radio tracked Lapwing chicks had no problems
getting through a 15cm hole diameter fence (Schifferli et al., 2006)).
Combination fences The main section of these fences is a barrier of wire mesh netting, usually high tensile steel.
Additional electric wires are then incorporated into the design to provide extra protection.
Commonly one or two electrified wires are put above the barrier, and one offset near the bottom of
the fence.
Advantages
• Durable: provides a more rigid fence-line than stranded electric fences.
• Low maintenance: less maintenance is required than a stranded electric strand fence
25
• Reliable: if something goes wrong with the electrical part, the fence can still act as a physical
barrier.
• Visual impact: low/medium, depending on the background habitat and whether there is
already stock fencing in the area.
• Flexibility: an existing stock fence can be improved with the addition of electric wires. Can
double as a stock fence.
• Effectiveness in situations with undulating or uneven ground: less complicated to install
without leaving gaps large enough for animals to get underneath than stranded electric
fencing.
Disadvantages
• Expensive: the barrier component makes the fence more expensive than electric strand
fences
• Effect on other species: potential effects on the movement of non-target species e.g. hares,
because of the small mesh size
Fence specifications Every fencing situation is unique, and the information provided below is not intended to act as a
substitute for the advice that can be obtained from qualified fencing contractors (preferably those
that have had substantial involvement in the construction of predator exclusion fencing). For
anyone intending to install a fence a fencing contractor should be their first point of call. Other site
managers with experience of predator exclusion fences in similar situations will also be able to
advise. However, before talking to a contractor or supplier, site managers should have an
understanding of the principles of predator exclusion fences to enable for them to make the right
choice of fence design and specification for their particular situation.
Contact details of some fence manufacturers and stockists is given in Appendix 4 and a list of RSPB
reserves with different types of fence, who will be able to advise for a given fence type/situation is
given in Appendix 5.
26
Chapter 3. Planning and installing an anti-predator fence, including Health
and Safety requirements and cost
Introduction
Factors to consider when thinking about installing an anti-predator fence include whether a fence is
the appropriate solution (including cost effectiveness), the type of fence, the cost, the route, Health
and Safety and maintenance requirements, local PR and the potential for vandalism.
The major potential negatives of fencing are visual impact on the landscape, restricting the local
movements of non-target species, especially hares (but also badgers, themselves predators of
ground nests), cost (materials and installation) and maintenance. Also, the practicality of fencing
large areas may in itself be a problem. The longest RSPB fences (enclosing up to 110ha) are
combination fences that also double as stock fences.
When designing a new wetland, the possible provision of a predator exclusion fence(s) in future
should be borne in mind. This will make subsequent installation easier by avoiding the need for
disruptive, and possibly expensive, groundworks after the reserve is established.
A disturbance licence will be needed if working near Schedule 1 species, such as stone-curlew or
little tern.
Key considerations when deciding whether to install a fence
When deciding whether to invest in a predator exclusion fence the key considerations should be:
• Number, distribution (current and likely future distribution and density of target species)
and productivity of the species to benefit.
• The configuration and extent of suitable breeding habitat.
• Non-target species and how the fence might affect them, including the status of other
predators which cannot be removed (e.g. badgers and red kites).
• Potential visual impact on the landscape
• The chances of flooding. (A temporary/portable strand fence may be the only option at sites
subject to regular seasonal flooding.)
• Cost (including prior groundwork to make installation easier).
Electric Fence Health and Safety requirements
Safety requirements
• Electric fence systems should comply to British and European Standards BS EN61011: 1992
(Mains powered) and BS EN61011-2: 1992 (Battery powered).
• British Standards require energy output to be less than 5.0 J and voltage to be less than 10
kV.
Fence positioning
• Fence lines should not lie within 2m of telephone lines or within 15m of power cables. If in
doubt, the relevant authority should be consulted.
• Fence earthing systems should be positioned at least 10 m away from any electricity supply
earth trip.
27
• Electric fences must not be installed within 2.5m of metallic equipment and services (e.g.
waterpipes/troughs).
• Avoid running electric fences parallel with any overhead power or communication lines, as
this can cause dangerously high voltage on the fence line.
• If the fence must cross overhead power or communication lines it must do so at right angles
and the fence must not exceed 2m in height.
• It is illegal to have two parallel electrified fences within 2 metres or each other
• For any two separate electric animal fences, each supplied from a separate energiser
independently timed, the distance between the wires of the two electric animal fences
should be at least 2.5 m.
• If the electric fence intersects a PRoW you must provide a non-electrified gate or stile so the
fence can be crossed. Allow persons to pass through areas of public access by means of
insulated gates, gate handles and insulated stiles.
Energisers
• Two energisers should never be attached to a single length of fence.
• The energiser must be turned off if there is a danger of flooding.
• Each energiser in use should be connected to a separate earth stake. No household wiring
or plumbing should ever be used for earthing.
• If possible an energiser should be installed indoors in a position which is free from any risk of
damage.
• If mounted outdoors, the energiser should be mounted on a substantial structure in a
position free from the risk of mechanical damage.
• Except for low output battery operated energisers, the energiser earth electrode should
penetrate the ground to a depth of at least 1m.
• A distance of 10m shall be maintained between the energiser Earth Spike and any other
earthing system such as the power supply system protective earth or the telecommunication
system earth.
Warning signs
• Where the general public has access to the fenced area, warning notices should be attached
to the fence at intervals no greater than 90 m.
• Where an electric fence runs along a public right of way clearly identify electric wires with
warning signs spaced not more than 50m apart.
• Where an electric fence crosses a public right of way clearly identify electric wires with
warning signs spaced not more than 10m apart.
• Signs should be at least 100mm x 200mm in size, yellow with permanent black inscription on
both sides and should use the words "ELECTRIC FENCE" and clamped to the fence.
Where to site a fence In addition to the H & S considerations above, the key factors influencing the route of a predator
exclusion fence should be:
• Landscape. The visual impact that the fence may have in the landscape can be influenced by
the chosen route. The fence should be sited where it will be the least visually intrusive e.g.
28
below a footpath so people see over it, in a ditch or with a hedge as a backdrop. It is worth
considering including buildings and hides as part of the predator barrier to remove the issue
of ugly fencing right in front of them.
• Location of suitable breeding habitat. Fences for wet grassland waders should encompass
both good nesting and feeding (chick rearing) areas. Fencing is not always practical at the
scale of the whole reserve, so choose the area where the target species density is high(est).
• Topography. The route should follow the line with least undulation in the ground surface,
the fewest ditch crossings (weak points of the fence) and the least changes of direction (high
tensile wire requires firm straining posts at every change in direction of the fence line).
• Potential archaeological restrictions (fences should not be installed on scheduled historic
and archaeological sites without specialist approval)
• Rights of way (there must be no blocking/restriction of access to PRoW or CRoW land)
• Access for maintenance
• Any new fencing on registered common land needs the permission of the Secretary of State.
Ideally, the fence should be erected so that it fully surrounds the target area. If this is not practical,
a strip of fence extending well beyond either end of the area to be protected might be worthwhile,
especially if access to ground predators at either end of the fence is difficult (e.g. restricted by water
or cliffs).
Fence design There is no single answer as to which is the best fence design available. The type used will depend
on a number of factors, such as the landscape, the target species (both predator and prey) and other
species present that might be affected by the fence, the amount of time available to staff, fencing
capabilities of staff, etc. (and these might differ between sites).
These are some factors to consider:
• A fence with unnecessarily small mesh is more expensive and unsightly.
• The spacing of stakes should not be unnecessarily close.
• Avoid irregular boundary shapes. High tensile wire requires firm straining posts at every change in direction of the fence line, which makes the fence more expensive.
Fence Cost Making comparisons between different fences is not easy, as prices vary depending on several
factors, including: the type of fence, whether installation can be done by site staff, the length of
fencing required, the number of corners, the access to the area, exact materials used etc. The
following are rough estimates and do not always include extra items, such as gates.
Barrier fencing There is no cost information for the type of barrier fencing used in Australia. Excluding the specialist
fence at Hodbarrow which cost £44.15 m-1, the average of three barrier fences installed recently at
RSPB reserves is £15.20m-1.
Combination fencing The average cost of 22 combination fences installed at RSPB reserves is £14.56 m-1 (range £ 6.5m-1 to
£27.11m-1). Several factors account for this wide variation in price, such as the individual contractor,
the amount of help with installation given by RSPB staff, the specification e.g. mesh size, number of
29
gates, the terrain etc. The new 2km fence around The Scrape at Minsmere cost £16.5 m-1, but a
further £97K was needed for a new sluice and earthmoving to enable easier and more effective
installation of the fence, which increases the overall cost to £65m-1! Natural England offer a
payment of £11.10/m for a combination fence under their new CSS scheme.
Strand electric fencing The cost of seven fences (9-12 strands) installed at RSPB reserves ranged from £1.27 - £8.89 m-1.
Fences installed by contractors were more expensive per m (£5.34 m-1) than those erected by RSPB
staff and volunteers (£2.42 m-1).
Rappa quote from £2.60 m-1 upwards, including installation, for a standard 9-wire electric strand
fence. Prices are particularly dependent upon the number of corners (turning points) in the fence,
and the amount of unevenness in the ground. At Ynys-hir, the fence materials, installation and
electrics came to a total of £3.50 m-1. Discounts may be available to the RSPB from some suppliers.
Natural England offers a payment of £2.85 m-1 for a 12 strand temporary strand fence under their
new CS scheme.
Temporary mesh electric fencing Agrisellex Electric Fencing Ltd charge £1.79 m-1 for electric poultry netting, Rappa £2.20-1 (including
polystakes), Gallagher Ltd. £3.16-1 (including integral posts).
Summary of fence costs
Fence type Average cost (£/m)
RSPB New CS payment rate
Strand 4.84 2.85
Combination 14.56 11.10
Barrier 15.201
1 Excluding Hodbarrow which cost £44.15 m-1
Fence construction Installation is generally considered to require skilled overseeing but local volunteer labour can often
help and save money. However, Sexton (1984) found that most faults in electric fences in the first
few weeks after construction were the result of human error. If possible, a contractor who has
previous experience in exclusion fencing should be sought to conduct or at least supervise
construction.
It is always worth seeking the advice of fence suppliers early in the planning stage. Tornado have
even produced a Fencing App (Fence Configurator) to help design and cost a fence. With the App
downloaded, to get an accurate plan of the fence on the ground simply walk the fence line, marking
where you want the end posts, strainer posts and gates on the app. When finished send the finished
track to your account on the Tornado website and follow the steps below.
30
Vandalism Fencing might be contentious at the consent stage, such as alongside properties, public rights of way
etc., although even combination fences can be no more obtrusive than some stock fencing.
Generally, the main complaints regarding electrified fences come from dog walkers. In the past, a
fence at Minsmere was persistently vandalised by one individual dog walker.
Twenty six percent of participants in an Australian survey noted vandalism or the theft of fence
components (mainly solar panels) as a maintenance issue. The motivation behind these acts of
vandalism was not clear. At some sites, signs had been erected to educate the public about the
purpose and importance of the fence in the hope that this will increase community support for the
site and assist in the detection of vandals and fence damage.
31
Chapter 4. Barrier Fences, their use, design and specification NB. Links to specific illustrated case studies in Appendix 6 are indicated in blue.
Barrier fence design and siting principles
Siting Fencing must not block/restrict access to CRoW land or impede rights of way. Barrier fences should
not be installed on scheduled historic and archaeological sites without specialist approval. There
may also be landscape considerations, so the fence should be sited where it will be the least visually
intrusive.
Fence material Depending on the situation, the vertical sections of barrier fences can comprise anything from
30mm diameter 1mm gauge galvanised wire chicken mesh fencing to full-height 2.5mm gauge high
tensile steel mesh deer fencing. Some barrier fences consist of chain link fencing, but this is
expensive and can be unsightly, especially if the wire is plastic-coated.
Height A vertical barrier needs to be minimum of c.2.1m to prevent a fox scaling it, unless it is protected by
an overhang. In many designs, the top of the fence is bent outwards to form a 45° straight
overhang. The overhang is more effective when it is bent to form a rounded arc (see specification
below) rather than a 45° straight overhang. Most rigid overhangs need to be used in conjunction
with electric wires to be effective (i.e. technically a combination fence). On their own, rigid
overhangs that extend as a horizontal or angled projection from the top of a fence, provide a
challenging but not impassable barrier for feral cats and foxes. For example, in Australia a fox has
been observed scaling a 1.8 m fence and then climbing upside down along the under-section of a
300 mm horizontal overhang. However, a 1.8m high wire netting fence with a foot apron and a
curved ‘floppy’ overhang effectively contained most foxes during pen trials and proved effective in
intensively monitored paddock-scale exclosures (Moseby and Read 2006).
To prevent animals burrowing beneath it, the fence should be buried 25cm – 45cm vertically into the
ground. (Note: Badger/foxes/otters can dig more easily into loosened soil. Therefore, if burying
netting vertically, the backfill must be placed on the inside of the fence, squashing the net onto the
hard (outward) face of the trench).
Unless the vertical fence is buried deeply, additional protection should be provided by a horizontal
mesh netting foot or apron at least 30cm wide (more usually 40-60cm) at right angles either buried
or laid on the surface (‘lapped’). If the apron is a separate piece of wire laid on the ground surface
(i.e. not the bottom of the vertical sheet of wire folded outwards) it should be butted against the
fence and secured by clips at close intervals to prevent feral cats, badgers and foxes from forcing
their way through. Similarly, the outer edge of the apron should be pegged down to prevent animals
burrowing underneath it. Where the edge of the apron curls and becomes proud of the substrate
(e.g. in bare areas), badgers will dig underneath (B. Yates per comm.).
Mesh size 7–8cm will exclude mature foxes and badgers, but still allow wader chicks to pass through (5cm may
be needed to exclude all otters). Some designs use two mesh sizes: smaller at the bottom (2-4cm)
32
which will exclude otters and fox cubs and a bigger mesh at the top. The bottom panel must
comprise at least 1mm gauge wire to prevent foxes from chewing their way through it, but the
upper panel can even be made of plastic.
Loosely tensioned netting Barrier fences often employ the concept of netting hung loosely to make climbing difficult. Loosely
tensioned netting can deter climbing animals e.g. cats and foxes by denying them stable climbing
footholds (Coman and McCutchan 1994). A floppy top should be formed from wire mesh at least
600 mm in length, enabling it to form a full semi-circle. There are varying interpretations of what
constitutes ‘floppy’ netting, but it should be as floppy as possible without reducing the height of the
fence (see images here).
Standard configurations
Foxes
The diagram above shows a typical specification for non-electrified barrier fence to stop foxes
predating poultry. An alternative is to bury the wire at a 45-degree angle, rather than at the 90-
degree angle shown above. The overhang would be better if it was formed into an arc and was
floppy rather than rigid (see below). The designed could be further strengthened by the addition of
a live wire(s). Two options are shown below.
33
Barrier fencing specifically against badgers Chain-link, weld-mesh, or similar heavy gauge fence netting of 8cm mesh or less can prevent access
by badgers. Badgers are good climbers, so where a free standing fence is used, it should incorporate
a supported overhang at the top, directed outwards from the area to be protected. The fence should
be at least 125 cm high and be buried to a depth of 60 cm. Alternatively, the mesh can be folded
outwards (lapped) on the ground surface for 40- 50 cm to deter badgers from digging through.
Tornado fencing produce a high tensile fence specifically designed to restrict badger movements.
Tornado HT Badger Fence is manufactured with high tensile wire which strains tighter than mild
steel and so requires fewer intermediate posts, making it quicker to erect. It does not stretch with
weathering so does not need to be retightened annually. The closely spaced vertical stay wires
(8cm) help prevent badgers from pushing through the fence. It can also be installed on post and rail
fencing.
34
Specification
Material Heavily galvanised steel wire
No. of Line Wires 15
Overall Height 158cm
Distance between stay wires 8cm
Top & bottom line wire specification 2.5mm dia - 1235-1390 N/mm2
Intermediate line wire specification 2.5mm dia - 1235-1390 N/mm2
Vertical stay wire specification 2.5mm dia - 695-850 N/mm2
Average weight per 50m roll 87.9kg
Installation A straining post is required at every major change in direction or any termination and should be
supported by a strut or box assembly. Netting should be tied off on the straining posts by hand or
with suitable joiners. When tensioning the fence the ‘crimp’ in the net should be reduced by
approximately 50%. Avoid driving staples tight against the wire as this will damage the galvanised
coating. The bottom 600mm can be buried and turned outwards to prevent badgers digging below
the fence. Two strands of barbed wire or a single electrified wire can be added to the top of the
fence.
Australian barrier fence designs against foxes and cats Extensive pen and field trials were used to test the effectiveness of different wire netting fence
designs as barriers to feral cats and foxes in South Australia (Moseby and Read 2006). A 180cm high
wire netting fence with a ‘floppy’ 60 cm overhang effectively contained most feral cats and foxes
during pen trials and proved effective in intensively monitored paddock-scale exclosures. The
overhang proved most effective when it was bent to form a rounded arc rather than a 45deg straight
overhang. A similar fence reduced in height to 115 cm did not reduce the effectiveness of the fence.
The two most effective designs are described in more detail below (Fig. 5).
For the taller 1.8m fence, treated pine posts were installed every 10m, and at every corner, and
extended from ground level to a height of 180cm. Seven selvage (i.e. support) wires were strained
at 30 cm intervals to increase the stability of the mesh fence. ‘Rabbit proof’ wire netting (40mm
diameter mesh, 1.4mm thick and 90cm wide) was clipped to the selvage wires between ground level
and a height of 90cm using ring fasteners. Wire netting of 50mm diameter, 1.4mm gauge and 120
cm height was clipped to the top section of the fence from a height of 90 cm extending 60 cm above
the top support (selvage wire). The 60cm wire overhang was bent to form a rounded arc extending
30cm out from the fence. Thicker lengths (4mm gauge) of high tensile spring steel were used to
support the ‘floppy’ overhang. A foot apron of 40mm diameter, 1.4mm gauge and 30cm wide wire
netting was clipped to the bottom selvage wire, extending out on the ground and buried on the
outside of the fence. Electric wires offset 80mm from the netting were provided at heights of 120
and 150 cm to give a shock to animals exploring the base of the of the overhang and further
improved the efficacy of the fence (Fig. 5).
The netting was better supported at posts and corners which made for easier climbing and so were
targeted by feral cats and foxes. For this reason, corners need special consideration during fence
planning and construction. Wherever possible, internal corners on exclusion fences should be
35
avoided. The efficacy of the fence was improved by replacing the timber posts with steel posts that
were harder to climb and adding extra netting at any corners to fill in any gaps in the overhang.
Subsequently, this 1.8m fence design, but without the addition of electric wires, proved effective at
excluding all foxes and feral cats from a 6000ha reserve in arid Australia for a 3.5 year period.
During pen trials, reducing the fence height to 1.15m but with the 60cm curved ‘floppy’ overhang
retained (Fig. 5) did not appear to reduce the effectiveness of the fence. Shorter 165 cm steel posts
were spaced 10m apart and five selvage wires were strained at heights of 0, 30, 65, 90 and 115cm.
The bottom and upper netting was to the same specification as the taller fence, as was the foot
apron (Fig. 5).
Moseby and Read (2006) thought that the animals in their study might have been discouraged from
jumping because the overhang curved back behind the animal, thus appearing to provide a
continuous roof. Although cats are wary of climbing unstable surfaces (Day and MacGibbon, 2002),
the ‘floppy’ nature of the curved overhang did not appear to contribute significantly to its success as
few animals actually attempted to scale it.
Fig. 5. Side view of two designs of barrier fence (Moseby and Read 2006). The 115cm fence with a ‘floppy’ overhang was just as effective at excluding foxes during pen trials as the taller 180cm version and would be cheaper and easier to install. A floppy-top fence design based around the one at the Arid Recovery Project in South Australia is
shown in Fig. 6. This uses hexagonal mesh but conventional square mesh netting of the appropriate
60
30
30cm 0
90
120
150
180cm
115cm
90
65
30
30cm 0
= selvage (support) wires
= electric wires (optional)
= 30mm diameter x 1.4mm gauge x 120cm width = 50mm diameter x 1.4mm gauge x 90 or 150cm width
36
mesh size would work equally well for the vertical fence section and the horizontal apron. The
curved top section needs to be ‘floppy’ and so something less rigid like chicken wire or even plastic
wire might perform better. The electrified wires are optional and if included would constitute a
‘combination fence’ (see below).
Fig. 6. A floppy-top fence design based around the one at the Arid Recovery Project in S. Australia.
Live wires at
120mm and 150mm
offset by 8cm
37
Fig. 7. Variations in the floppy-top design. Floppy-top fences at the Arid Recovery Project site (left) and at Heirisson Prong (right). Note the heavy rubber matting along the apron of the Arid Recovery Project fence to prevent the wind from excavating the sand below the fence.
Straight line barrier fences on dry land In some situations, rather than enclosing an area of high conservation value, a straight line barrier
fence can deny ground predators access between features that cannot be traversed by them such as
the sea and/or cliffs e.g. across a peninsula. Such a barrier fence excludes ground predators from
the Peron Peninsula in Australia by extending a considerable distance into the sea at either end to
prevent foxes from passing around the end of the fence at all states of the tide. However, it is
difficult to curtail the passage of foxes around the seaward ends of fences (Patterson 1977, Short et
al.1994) and all three fences in Australia that cross peninsulas have experienced this problem.
Barrier fences have been installed across two islands of c.6 and 7ha in Lower Lough Erne specifically
to restrict the area available to badgers living on the islands to allow wet grassland waders to breed
in the remaining badger-free area. (RSPB failed to get permissions to trap and remove the badgers).
On one island a single badger remained within its confined area until it died of natural causes 2 years
after the fence was installed. The other fence was installed across an island with a sett occupied by
up to six badgers. One badger swam around the end of the fence but would not re-enter the badger
side of the fence, stopping at the (open) gate in the fence. It was concluded that the animal might
have been excluded from the sett and driven into the water by the other badgers hence its
reluctance to go back across the threshold.
Barrier fences in water There is little published information on the efficacy of barrier fences installed directly into water.
The basis for this type of use is that a swimming fox or badger will not be able to obtain sufficient
purchase to climb over a fence placed vertically in water.
38
Barrier fences around islands Until recently, in the UK barrier fences have only been installed around islands in lagoons (e.g.
Titchwell) or water-filled pits resulting from mineral abstraction (e.g. Rye Harbour). Usually they are
anchored to the floor of the water body with a metre or so of the fence above the surface.
Since 1999, barrier fences have been used at Rye Harbour to try to exclude foxes and badgers from
accessing individual islands hosting colonially nesting gulls or terns. Originally, the fences comprised
10cm hexagonal mesh fencing, which successfully excluded foxes and badgers (a smaller mesh
would be needed to exclude otters). The current specification uses standard sheep netting with
15cm verticals (but installed upside down with narrower mesh at top). This design has also been
used in a ditch to prevent crossing by foxes and badgers and also for keeping dogs away from sheep.
Recent fences at Rye Harbour have used horse netting with 8cm vertical spacing.
Based on experience at Rye, if the aim is to exclude foxes or badgers the fence need not extend
more than 30cm above the water at lowest water levels and does not need to reach the bottom of
the pit (B. Yates pers comm.). Of all the fence designs employed at Rye Harbour, barrier fencing
around islands offers the best results, incurs low cost and has low maintenance requirements (the
fences have similar longevity to those on land and with relatively low visual impact (B. Yates pers
comm.). Even if the waterbodies have a perimeter anti-predator fence of some kind it is still worth
putting fence around each seabird island in case the perimeter fence fails (B. Yates pers comm.).
Floating fences It is possible that a floating fence, like the anti-goose fences at Hickling (Fig. 8), around a breeding
island might be a sufficient barrier to prevent access by a swimming fox or badger.
Fig. 8. Floating goose fence at Hickling Broad.
Even just a floating boom might be sufficient. This is something that should be trialled, perhaps in the first instance against a swimming dog. Darcy (http://www.darcy.co.uk/) can supply a 70cm Trident boom with a 28cm freeboard and a 42cm draft costing £1100 per 25m (Fig. 9.). Its longevity
39
is unknown and the colour is off-putting. Like the floating goose fence, it might prove to be a barrier to swimming wader chicks (even young avocets might not be able to dive underneath a 42cm draft).
Fig. 9. Floating boom
Recently, a floating fence has been installed around one of the islands in a former gravel pit at Fen
Drayton, which is in an active floodplain. The purpose of the fence is to stop terrestrial predators
such as foxes from accessing the island, which will hopefully improve the productivity of species
which nest there such as common terns, black-headed gulls and avocets. It will be interesting to see
how effective the fence proves to be and how the fence fares when the reserve floods.
A word of warning: potential problems with fencing seabird nesting islands At Titchwell, a small island in the fresh lagoon is surrounded by a barrier fence against otters and
foxes. In 2017, there were 530 nests of black-headed gulls and over 40 avocet nests within the
fence. The small size of the island means that a large number of birds are squeezed into a small
area. When the island is disturbed the chicks head for the safety of the water. In 2017, when
disturbed a small number of the larger chicks managed to get stuck in the fence or got through the
fence but were then unable to get back again and so become separated from their siblings.
Although only a very small proportion of chicks died, which would not outweigh the benefit of the
fencing, it is potentially distressing to visitors and staff and the gulls.
This problem has not been encountered at Strathbeg where the same 50mm mesh fencing is used
but there the whole pool is fenced, rather than just the nesting island or at Rye Harbour, where the
fences in water have a larger mesh size as otters are not a concern (B.Yates pers comm.).
Fitting a strip of chicken wire along the bottom of the mesh fence would prevent gull chicks from
getting trapped, but the height of the strip would need to be sufficient to cope with fluctuating
water levels. However, this solution might prevent avocet chicks from leaving the island. Working
on the principle that wader chicks will always walk or swim along fence lines looking for a way out
(based on experience of catching waders in traps), a funnel shaped exit at fence corners would
enable them to leave. Although wader chicks will be able to swim/walk out of the exits (but not find
their way back in), predators will walk/swim past them and not find their way into the fenced area.
However, unless otters are a specific problem, it is better to use a larger mesh that will exclude foxes
40
and badgers and still allow gull and wader chicks through. The normal recommendation for the
minimum mesh size to exclude foxes is 8cm but a swimming fox might find it hard to get through a
mesh significantly larger than this, so 10cm might suffice if the entire fence was in water.
Fences in perimeter ditches At Elmley NNR, a 6km barrier fence has been installed within a water-filled perimeter ditch around
c.300ha of wet grassland to protect breeding waders from fox predation. Similarly, at RSPB Wallasea
a barrier fence has been installed in a specially constricted perimeter dyke to protect c.80ha from
incursions by foxes or badgers.
Barrier fence installed in water between the ‘mainland’ and a breeding island Barrier fences have been installed to provide a barrier to foxes and badgers in the water between
the ‘mainland’ and a breeding island at Hodbarrow, Lower Lough Erne, and Conwy RSPB reserves
and Rye Harbour). Although, so far this type of fence appears to be effective, at Hodbarrow there
have been night time sightings of a fox attempting (unsuccessfully) to get round the fence by
swimming up and down it before returning to the mainland. If swimming mammals behave like
birds, one potential way to discourage them from swimming around the end of the fence, would be
to put an extension in the water at right angles (see diagram below). The (untested) theory is that a
mammal will concentrate its efforts to penetrate the fence at ‘X’ and will eventually give up and
swim back to shore. The obvious snag with this that it creates a corner where the animal might be
able to brace itself against the fence and be able to climb it. This could be prevented by putting a
floppy top along this section of fence or at least some kind of overhang. This idea has yet to be
trialled or tested.
Barrier fences around whole waterbodies The only UK example of a non-electrified standard barrier fence on dry-land to protect a significant
area from incursion by large ground predators is at Upton Warren Nature Reserve, managed by
Worcestershire Naturalists Trust. However, in one place a section of the Wallasea barrier fence exits
the perimeter ditch to go round a major sluice. The design of this section was based on the lower of
the two barrier fences in Fig. 5 (above) and has a curved, but fairly rigid, top.
Island 900
Mainland
Fence X
41
Chapter 5. Combination Fences, their use, design and specification
Use Semi-permanent anti-predator fencing is often the best option for sites where fencing is required in
the same location each year. On reserves the principal use of combination fences is to try to exclude
foxes and badgers, either to protect the nests and chicks of waders breeding at wet grassland sites
or around whole lagoon/scrape complexes to protect breeding avocets, other waders, gulls and
terns nesting colonially on islands within the lagoon. Combination fences are also used to protect
stone curlews nesting in open dry grassland. For species other than seabirds, the fence should
encompass both good nesting and chick feeding opportunities, and protect a sufficient area to
benefit a worthwhile number of the target species.
For sites where there are either few staff, little time available for maintenance or a lack of fencing
expertise, a combination fence works best. A combination fence is more expensive, more difficult
and time-consuming to install than a conventional nine+ strand electrified fence, but it is friendlier
to wader chicks and hedgehogs, has a longer lifespan and is effective against both foxes and
badgers. Less vegetation control is required than for stranded electric fences, there are fewer
electric wires to check and maintain, the fences are far more rigid and so less prone to damage and
it is less of a worry if the electrics do fail for any reason.
Combination fences also work better in undulating terrain than a stranded electric fence for which
maintaining the correct wire spacing is critical to their effectiveness. Uneven ground makes it
difficult to keep the correct wire spacing without leaving gaps large enough for animals to get
underneath and the extra posts needed to achieve this increases the cost. However, unless carefully
sited a combination fence is more visually intrusive than a strand fence, but no more so than an
ordinary stock fence. Combination fencing can also serve as a stock fence, especially if a single
strand of barbed wire or a single electrified strand is run around the inside to stop stock rubbing
against it.
Currently, RSPB has not fenced a single area greater than 100ha with a combination fence but there
are no overriding practical reasons why larger areas should not be fenced in this way.
Siting For most species, the fence should contain both good nesting and chick feeding opportunities.
Fencing should be located away from tall vegetation and must not block/restrict access to CRoW
land or impede rights of way. Combination fences should not be installed on scheduled historic and
archaeological sites without specialist approval. There may also be landscape considerations, so the
fence should be sited where it will be the least visually intrusive. If the fence has landscape impacts
and is near reserve boundaries next to other properties, it would be wise to check with the planning
authority whether planning consent is required.
Design principles
The barrier Usually comprises a combination of permanent net fencing (e.g. Tornado high tensile stock fencing)
and electrified wire strands.
42
Height The recommended overall above ground height of the finished fence should be at least 1.5m (at
Otmoor a fox was able to jump over a fence 1.35m high). To prevent animals burrowing beneath it,
the fence should be buried 30-45cm vertically into the ground. For additional protection there
should be a horizontal mesh netting apron at least 30cm wide at right angles either buried or laid on
the surface up against the outside of the fence.
Mesh size 8cm will exclude fully-grown foxes and badgers (but not all otters) and still allow wader chicks to
pass through. (A badger has been seen to squeeze through the 8cm combination fence at Greylake
(Harry Paget-Wilkes pers comm.). It was inside the fence (possibly having dug under or scaled the
fence).and was desperate to get out. This took about 10 minutes (having initially appeared to be
stuck) and left blood on the fence. The average skull width of an adult badger is c.8cm and there is no
evidence that badgers are regularly getting through other 8cm mesh fences.)
Wire spacing Electric wires placed above the mesh barrier must be closely spaced to form both a physical barrier
and an electrical deterrent (see below) if they are to function effectively. A wire spacing of c.8 cm
immediately above the netting increasing to c.12cm at the top of the fence, where less of a barrier is
required, should help prevent foxes from getting through it.
Badgers A series of one-way badger gates should be installed so that if badgers manage to penetrate the
fence they can always get out (see here).
The electric fence component Although both cats and foxes are capable of jumping to heights of approximately 1.8 m (Day and
MacGibbon 2002), they are most likely to jump onto the fence at lower heights. Cats most often
jumped onto the fence at heights of 1.2 –1.5 m (Moseby and Read in prep.). Three electric wires
spaced at c.8cm (live), 18cm (earth) and 30cm (live) above the fence should prevent foxes and cats
from getting over it.
An electric wire offset c.8cm out from the fence on insulators and about half way up (c. 65 cm above
ground) is often used to try to deter climbing foxes and cats. The effectiveness of electric wires used
in this way is unknown but they are unlikely to be as effective as the electric wires used at the top of
the fence.
A much lower offset electric wire(s) can be used to train animals to avoid the fence, lessening the
risk of breaches. This should be positioned at the height of the target animal’s snout to encourage
investigation (c.10-20cm). However, the lower the electric wire the more frequent the need to cut
vegetation to prevent it from touching the live wire and causing the wire to short out.
The recommended standard configuration Based on the above design principles, the typical specification involves the use of standard 8cm
mesh (the horizontal distance between the vertical wire stays). (Tornado also supplies fencing
(badger fencing) with 5cm between the vertical wires. This will exclude otters and fox cubs but is
33% more expensive and more visually intrusive. Think carefully whether you need it.)
43
Tornado high-tensile stock fencing is supplied in three widths. The two most commonly used widths
for predator exclusion fencing are 158cm and 194cm (Fig. 10).
The 158cm fencing is buried about 25-30cm deep vertically into the ground by using a trenching
machine, leaving c.1.3m above ground. Three high tensile electric wires are installed spaced at
c.8cm (live), 18cm (earth) and 30cm (live) intervals above the fence, creating a c.1.55-1.66m high
barrier. This design of fence would benefit from an additional horizontal wire apron or foot at least
30cm wide to reduce the potential for animals digging beneath it. This could be a separate width of
wire (e.g. chicken wire) or, rather than burying the fence vertically, it could be bent to make a
horizontal apron continuous with the vertical netting and lying flat on the ground surface (Fig.
10(b)). Alternatively, if the wider width of netting is used, it can be bent at right angles to make a
horizontal 35cm apron continuous with the vertical netting, but buried at a depth of c.25-30cm (Fig.
10(a)). This is probably the best way of preventing animals from burrowing under the fence but it
makes the fence more awkward and time-consuming to install.
The standard combination fence design has another electric wire offset c.8cm out from the fence on
insulators about half way up (c.65 cm above ground). This is probably less critical than the electric
wires at the top of the fence. Alternatively, a lower offset electric wire roughly at the height of the
target animal’s nose (10-25cm above ground) can be used to ‘train’ animals to avoid the fence.
Fig. 10. Recommended designs for combination fences using (a) Tornado HT17/194/8 fencing or (b)
Tornado HT15/158/8 fencing, which can be buried vertically or bent to form an apron on the surface (as shown).
130cm
30cm 30cm 30cm
130cm
8cm 8cm
10cm 10cm
12cm 12cm
(a) (b) Live wire
Earth wire
8cm mesh fencing
Offset 6-8cm
65cm 65cm
44
25-45cm
Live wire
Live wire
Live wire
Earth wire
60-65cm
8cm
10cm
12cm
Ove
rall
fenc
e he
ight
1.6
m
1.3m
Fig. 10c. Standard configuration for combination fence (side view).
Variations to the recommended basic design The specification in Fig. 10 is appropriate to situations where the bottom of the fence can be buried.
However, in some situations such as on shingle, this is not possible. At Rye Harbour the bottom of
some lengths of fence runs flush to the ground and has no buried section or apron because this
would have caused too much damage to the shingle. This means that 1220mm high Tornado fencing
could be used for the main fence, with 2 electrified wires above to bring the overall fence height to
1.5m. (Having three wires, the middle an earth, might have been even better and increased fence
height to >1.60m.)
Configuration of live wires The design used at Rainham (Wennington) has an additional off set live wire that increases fence
height to 170cm (Fig. 11).
45
Fig. 11. The arrangement of electric strand wires above the fencing barrier at Wennington
(Rainham). Note the additional live wire on the inside of the fence to stop stock rubbing
against it.
Mesh size Several RSPB reserves have opted for a mesh size of 5cm to exclude young foxes and otters.
Tornado now stock this product as a special netting designed for anti-predator fences (R18/170/5 C5
PREDATOR FENCING) and it was used for the latest combination fence at Rainham. The vertical stays
in the netting are 50mm apart and the horizontal lines 100mm apart to give a mesh size of 50mm x
100mm for the full height of the netting. One advantage is that the vertical stay wires can become
distorted and the wider opening still not be wide enough for a fox to squeeze through (see below).
Effectiveness There is no evidence of mature foxes gaining access through a fence to the standard specification
above (8mm mesh) that has been correctly installed and maintained (but see here). Gates, ditch
crossings and strainer posts are potentially the parts of the fence most vulnerable to penetration by
predators and should be kept to a minimum.
A buried apron should prevent badgers digging under the fence but this has happened on two
occasions at Cavenham, even though the fence is believed to conform to the specification above (D.
Rogers pers comm.). At Minsmere even a persistent badger was not able to dig under the fence and
eventually it was deterred from further digging attempts by a single strand of electrified wire
running along the fence at nose height (A. Needle pers comm.).
Fencing to 130cm
above ground level
Off set live wire at 172 cm
Live wire 160cm
Earth wire 148cm
Live wire 138 cm Off-set live
wire at 65cm
46
Factors to consider when deciding the route of the fence Enclosing larger areas is more cost effective and more likely to protect a significant population of the
target species. Choose a route for the fence that makes it the least visually intrusive (e.g. against a
boundary structure such as a bank or hedge and below perimeter paths so people look over rather
than through the fence) and that involves the least number of direction changes, which then require
a strainer post. As far as possible avoid undulating ground. Minimise the number of gates and ditch
crossings and leave sufficient width between the fence and boundary structures to allow vegetation
management (grazing or mowing with a tractor, ATV or even a strimmer), but beware of damaging
the fence.
Gates The protection provided by the fence should be continued across gates (see below). Gates in
combination fences should be meshed. The same configuration of electric wire strands should be
continued across the gate attached to isolator steel springs allowing the strands to be removed to
allow safe access through the gate when needed. Wooden sleepers or stone should be dug into the
ground at the base of gates to prevent animals from digging under them.
Gaps frequently form between double opening vehicle gates and therefore a wide, single, vehicle
gate is preferred. When gates are secured with a chain and padlock the chain should be shortened
so that the ends of the chain just meet, and the gate must be tightly fastened. A more secure locking
mechanism that ensures the gate is correctly aligned when closed is preferable to a simple chain and
padlock system.
Ditch crossings Ditches are potential weak points where foxes can enter. A section of mesh fencing placed vertically
in the ditch where the fence crosses it can prevent this. At Rainham, the solution has been a barrier
within the ditch that rises and falls with changing water levels (Fig. 12).
Fig. 12. The floating section of the combination fence at Wennington (Rainham).
47
Where the impact on otter movements is a concern, the section of the fence line can be adapted to
allow access to otters through the ditch but reduce the risk of foxes entering (Gulickx et al. 2007).
The ‘water pathway' (Fig. 13) is 1m deep and 3m wide perpendicular to the electric fence (which
passes overhead), with the banks clad with wooden boards to ensure they do not collapse. These
vertical banks also ensure that passing through the channel beneath the fence can only be achieved
by swimming. This allows otters to enter the washland habitat whilst restricting access to foxes
which are thought less likely to swim. The ends of the pathway are vegetated with reed and other
riparian plants, and the banks are gently sloping (c.30 deg.) to provide good access for otters. There
was no evidence that foxes entered the site by this route but otters did, although it might be
different if the ditch was to freeze over or dry up.
Fig. 13. Combination fence ditch crossing to allow otter movement. Ditch sides have been
steepened using boards, to reduce the risk of foxes using it as an entry point.
Installing a Combination Fence Installation of the barrier part of the fence is best carried out by a fencing contractor; because of the
equipment required it would be difficult for site staff to install the fence to the required high
standard. However, it might be possible for reserve staff to install the electric wires themselves to
reduce costs. An example of the specification to give to a contractor is given below Table 2)..
One thing to avoid when installing the fence is distorting the vertical stays and widening the gap
between them, for example by over tightening (see here).
48
Table 2. Specification for a standard combination fence.
Feature Elements
Livestock netting
• high tensile steel wire and 6 - 8 cm wire mesh
• 1.3m above ground height
• 0.25-0.3m buried below ground (to prevent mammalian burrowing) and/or
• a 30cm wire netting apron butted against the fence lying flat on the ground surface and pegged at intervals
Wooden posts
• Sweet chestnut (better) or softwood (cheaper). Tanilised (i.e. treated with TANALITH™ E wood preservative) or treated with Tuffdip (bitumen based and better for the aquatic environment than creosote). Forest Stewardship Council (FSC) certified, ideally locally grown and manufactured.
• 2.4 metre full round 100mm posts at 4 metre intervals.
• Full round 150mm 3 metre strainer posts where needed at changes of direction and at 100 metre maximum intervals. Minimise external fence features, such as strainer post stays, which will aid animals that attempt to climb or jump the fence.
Electric wires (2.5mm
diameter high tensile
steel strands)
• Live strand (1) 0.60-0.65m above ground and off-set by 80mm
• Live strand (2) c.8cm above the top of the mesh fence
• Earth/neutral strand (1) c.18cm above the top of the mesh fence
• Live strand (3) c.30cm above the top of the mesh fence
Signage • Where the general public has access to the fenced area, warning notices should be attached to the fence at intervals no greater than 90m
Electric fence gates
• Bespoke gates (12ft single or double gateway 10ft each) within the perimeter. (NB. Gaps frequently form between double opening vehicle gates and therefore a wide, single, vehicle gate is preferred. A more secure locking mechanism that ensures the gate is correctly aligned when closed is preferable to a simple chain and padlock system. When gates are secured with a chain and padlock the chain should be shortened so that the ends of the chain just meet, and the gate must be tightly fastened.).
• Meshed as per fence
• Electric wires as per fence and isolator steel springs across gates for safe access
• Wooden sleepers dug into the ground at the base of the gates to prevent digging under
Ditch crossings • Extend the non-electrified stock netting fence downwards into the ditch to prevent access under and through the water.
49
Fig. 14. The standard combination fence at Otmoor incorporating the features described in Table 2
(but with three rather than four strands above the barrier). Note that the top strand is marked at intervals with twists of white/orange electrical insulating tape to reduce bird strike risk and to deter deer from trying to jump over.
Cost of combination fencing This is difficult to specify as it depends on amount of ground preparation e.g. to reduce undulating
ground or built up where fence line crosses water, whether the apron is buried or on surface, the
number of gates etc. The new 2km fence around The Scrape at Minsmere cost £16.5/m in 2015
(plus another £97K for a new sluice and earthmoving to enable easier and more effective installation
of the fence). For a straightforward installation the cost of a combination fence should be c.£15-£17
per m. Site managers should try elsewhere if estimates are substantially more than this. The new
CSS capital payment for anti-predator combination fencing of £11.10 per m is probably on the
optimistic side.
Fence operation Some permanent fences are deactivated or intentionally breached by opening gateways in the
winter to allow movements of non-target species, especially brown hare Lepus europaeus. The
fence is switched back on prior to the wader breeding season. Once the fence is activated, you
should regularly check that the target predators are absent from the enclosure, for example by the
use of trail cameras or checking for footprints and by monitoring wader settling behaviour. If hares
are not a problem the fence should be kept operational throughout the year i.e. with the live wires
electrified.
50
Chapter 6. Permanent/semi-permanent electric strand fences
Use Semi-permanent anti-predator fencing is an option for sites where fencing is required in the same
location each year i.e. the target bird species breed in the same area each year and the site is not
subject to regular flooding. Electrified strand anti-predator fences can be effective against large
ground predators such as foxes and badgers but are not recommended for excluding hedgehogs (see
later).
At RSPB reserves, the principal use of strand fences is at wet grassland sites to exclude/deter foxes
and badgers from areas with wader nests and chicks. A conventional nine+ strand electrified fence is
much less expensive and easier to install than a combination fence, but it is less durable and has a
shorter lifespan before needing major maintenance (8-10 years). Electric strand fences require more
frequent maintenance than combination fences, especially vegetation control, to maintain maximum
effectiveness.
Strand fences are less conspicuous than a combination fence and for this reason may be the
appropriate option if there are overriding landscape considerations. Also, where there is likely to be
some shifting around of the fence-line, for example near ditches on peat, the stranded electric is the
easiest type of semi-permanent fence to change and adapt. The corner straining posts may need
relocating, but after this, the metal stakes in between are simple to reposition.
Currently, RSPB has not fenced a single area greater than c.50ha with a strand electric fence and the
high maintenance demand would make fencing areas much larger than this impractical.
Siting Electric strand fences rely mainly on providing an electric shock for their effectiveness and ensuring
this is the major factor influencing where they can be sited. Trying to install stranded electric
fencing becomes complicated at sites with undulating or uneven ground, because it is difficult to
keep the correct wire spacing without leaving gaps large enough for animals to get underneath. The
cost increases too because of the extra posts needed. Also, the fence must remain clear of water at
all times. For these reasons, often the best option is to run the fence along an existing bank or one
constructed specially for the purpose.
If protecting breeding wet grassland waders, the fence should encompass both good nesting and
chick feeding opportunities, and protect a sufficient area to benefit a worthwhile number of the
target species. The fence must not block/restrict access to CRoW land or impede rights of way.
Where there are landscape considerations, the fence should be sited where it will be least
conspicuous. Fencing must be located away from tall vegetation that would short out the electric
current and reduce the voltage making the fence ineffective as a deterrent.
Because of the high maintenance requirement of strand fences, sufficient space should be left to
allow vehicle access around the outside of the whole fence-line, which decreases the time needed to
check and maintain the fence.
51
Design principles Permanent electric strand predator exclusion fences work by combining the ability to provide a
severe electric shock to modify the behaviour of the predator with at least a weak physical barrier
(the fence) as a second line of defence. To be effective, permanent electric strand fences need to
have closely spaced wires, close enough to prevent the animal from stepping through or putting its
head between the wires without touching them, and be taller than the animals being excluded. One
of the electrified wires should be at the animals' nose level. Fences have mains electricity or a
battery powered energizer attached to the wires to produce a short but nasty shock (c.6-8kV) when
a wire is touched. Predators associate the unpleasant shock with the fence and this creates a
psychological barrier that discourages them from touching it again i.e. the predator learns to avoid
the fence (McKillop et al., 1999).
Stranded wire fences (polywire or high tensile steel) supported by wooden posts are the most
common fence materials, but electrified mesh can be used. However, electrified mesh is generally
used for temporary fencing (see next section). The most effective semi-permanent electric fences
utilise high tensile steel stranded wires rather than polywire.
Principles of effective fence design
Alternating live and earthed wires To work effectively, the current needs to pass through the animal from a live wire to an earth.
Relying on transfer from a live wire to the ground and back to the unit is unreliable, so strand fences
normally feature alternating earth and live wires.
Earthed wires are added to the system so that they alternate with live wires in such a way that
animals pushing through the fence touch both live and earthed wires simultaneously. This earthing
design is likely to result in a more severe shock being received by the animal than that received
when the animal is earthed solely through its paws. However, the closer the wires, the less the
shock sensation that will be felt, as it is proportional to the distance the current travels through the
animal’s body.
For animals trying to jump through fences, the use of alternating live and earthed wires can also
ensure that the animal will actually receive a shock which would not be the case if it was off the
ground when in contact with an all live wire fence. The main drawback to the use of earthed wires is
that it increases the likelihood of a dead short if live and earthed wires come into contact. Therefore,
adding extra live wires should always be considered as well.
For animals which try to crawl under the lowest electrified wire, insertion of an earthed wire close to
the ground is often the only feasible means of preventing them penetrating the fence in this way.
The earthed wire is positioned close to the ground so that the animal must pass over it, forcing it up
and into contact with the lowest electrified wire. Inserting an additional electrified wire so close to
the ground would be impracticable as inevitably it would result in the fence being short circuited by
touching the ground or vegetation.
Digging under electric fences is not usually a serious problem. Rabbits and badgers both dig under
wire netting fences but rarely burrow under electric fences. Presumably, receiving shocks deters
them from spending the time required near to the fence to dig under it. However, as an extra
measure to stop badgers digging under a strand electric fence, a single barbed wire strand can be
52
run on the surface of the ground directly under the fence and pegged down by the fence posts (Lee
Marshall pers comm).
Wire spacing Wire spacing should be close enough to prevent the animal from stepping through or putting its
head between the wires without touching them. One of the electrified wires should be at the target
predator's nose level.
A general spacing guide for electric strand fences against different species is given below (Figure 15).
However, recommended spacings vary between fence suppliers. On the basis of trials, Coman and
McCutchan (1994) recommend wire spacings for foxes of 70 – 90 mm, but also found that with dead
foxes even a spacing of just 75 mm did not guarantee an animal with dry fur would receive a shock
when passing between the wires.
Fig. 15. Rutland Electric Fencing wire spacing guide for electric strand fences. Live wires are shown
in red, earth wires in brown. An electrified wire above the animal’s head is recommended for species that habitually jump.
Type of wire Given that the level of contact determines, to some extent, the severity of the shock and the
subsequent reaction (McKillop & Sibly, 1988) the use of a thicker conducting wire is likely to produce
a more pronounced adverse response, leading to greater effectiveness. For high tensile steel wires,
most specialist fencing companies specify 2mm diameter wire.
10 cm
5 cm
10 cm
5 cm 2.5 cm
10 cm
10 cm
2.5 cm
5 cm
5 cm
5 cm
10 cm
10 cm
10 cm
10 cm
15 cm
20 cm
25 cm
20 cm
Otter 5 wire
Badger 5 wire
Fox 9 wire
53
In field trials both steel wire and polywire fences had the ability to exclude badgers provided fence
voltages were maintained at a suitable level (MAFF 2001). The steel wire was 2mm in diameter and
constructed from seven twisted strands of galvanised steel. The polywire was 2mm in diameter and
composed of three, 0.2 mm steel conducting wires interwoven with plastic strands. However, steel
wire is the more effective conducting material and deterred badgers at a lower voltage (4 kV) than
polywire (6 kV). Over a range of test voltages, the steel wire fence was more effective than its
polywire counterpart at the same voltage. Steel wire is also more durable than polywire, tensions
over greater distances and can carry a higher voltage.
Strand Fence specifications The recommended specifications for badgers and foxes differ in overall height and the number of
wire strands (Fig. 16).
Fig. 16. Two commonly used strand electric fence designs against foxes (standard Rappa 9 strand)
and badgers (as recommended by Defra).
Badgers The specifications recommended for badgers by Defra were developed from enclosure trials
(McKillop et al. 1999). They found that a 30cm high fence comprising four electrified wires close to
the ground (first strand above 10cm above ground and then 10cm apart) were sufficient to deter
badgers. The wires, which are all live, are held by adjustable plastic insulators supported on wooden
stakes. A viable alternative is to use plastic "tread-in" posts which provide both the posts and
insulators in one item. The corners and ends are normally more robust wooden posts with
insulators applied.
The fence should be powered by a 70 Ah battery-operated energiser producing a pulsed energy
output of 1.5 J into a resistance of 500 ohms. This specification generates a maximum voltage of
around 6 kV when earthed using 50 cm copper rods and complies with British Standards which
require energy output to be less than 5.0 J and voltage to be less than 10 kV.
105 cm
84
66
50
38
28
20
13
5 cm
20
30 cm
15
10 cm
Live
Earth
54
One commercially available strand fence against badgers (Rutland Electric Fencing) adds an earth
wire at ground level forcing a badger into contact with the lowest electrified wire if it tries to get
beneath it. The earth wire acts as a ground levelling line and should be stapled to the posts which
should be a maximum of 10 m apart, although ground undulations usually dictate closer spacing.
Table 3. The standard specification of electric fencing to manage badgers. Earth wire shaded.
Strands Height from ground (cm)
Defra (McKillop et al. 1999). 4 10 15 20 30
Rutland Electric fencing 5 0 10 15 20 30
It is important to ensure the continual electrification of the fence during the first few weeks after
installation. During this period, badgers first encounter the fence and establish their future patterns
of behaviour in relation to it. If their initial experience with the fence is a bad one, brought about by
the receipt of a relatively severe shock, they are likely to avoid the area and thus the effectiveness of
the fence is enhanced. Conversely, if they learn to cross the fence at this early stage, subsequent
crossings are far more likely, even when the fence is electrified.
Most badgers are likely to investigate a new fence within the first 24-48 hours, so it is important
that the fence is electrified 24-hours a day straight after installation. Over the first 2-3 weeks,
badgers will repeatedly investigate the electric fence, looking for ways to get through or around.
During this time, they will receive a number of electric shocks and, eventually abandon trying to
access the protected area. Fence voltages should not be allowed to fall below 4 kV, particularly
during the first few weeks after installation. (NB. Some energisers have a night-time setting to
reduce power after dark so ensure that this is switched off!).
Fence inspections should be conducted at one to two day intervals during the first two weeks after
installation. Subsequently, when behavioural patterns have been established, the interval between
visits can be increased to one to two weeks, especially outside the breeding season.
Foxes The specification recommended by Defra for electric strand fences against foxes was also developed
from enclosure trials (McKillop et al. 1999). It comprises eight alternating live and earth wires
making a total height of 105cm. The alternating design is to prevent foxes from jumping straight
though the fence. Commercially available electric strand fences against foxes have broadly similar
specifications (Table 4), but some include an extra live wire.
Table 4. The Defra recommended wire spacing for strand fences against foxes compared with some
commercially available equivalents (shaded - earth wires; unshaded - live wires.)
Strands Strand configuration from ground level upwards in cm
Defra (McKillop et al.
1999)
8 5
15 25 35 45 60 80 105
Rappa 9 5 13 20 28 38 50 66 84 105
Electric fence online 8 10 20 30 50 70 100 120 140
Rutland Electric Fencing 9 5 15 25 35 45 60 80 105 125
55
Originally, the standard Rappa fence design was the one most commonly used on RSPB reserves (Fig.
17).
Fig. 17. Rappa nine strand electric fence design to exclude foxes
Otters Rappa sells four or six wire strand fences to exclude otters. Once installed the system is claimed to
robust with a life span of many years with a minimum of maintenance. The cost works out at about
25% of a conventional otter fence made of wire mesh. Its effectiveness is unknown. Rutland Electric
Fencing recommends a five wire fence with the extra wire an earth close to ground level.
Variation from the standard configuration. Unfortunately, at some reserves we wish to exclude both foxes and badgers from the same area.
This is more challenging for electrified strand fences than for combination fences. At RSPB Greylake,
the first design had an extra strand with live wires ‘bunched’ near the bottom of the fence to try to
dissuade badgers from poking their noses through the fence and then making a dash through it
(Table 5). It was not totally effective against badgers and there were occasional incursions by foxes
after problems had developed with the fence. Rappa strongly recommend against increasing the
number of live wires, because to be effective the current has to pass through the animal from a live
wire to an earth wire and that relying on transfer of current from live wire to the ground and back to
the unit is unreliable. As a result, to reduce incursions by badgers the total number of strands was
increased from 10 to 12, the polywires were replaced by high tensile steel wires and a better
energiser was acquired. The upgrading prevented incursions by foxes, but in the third year badger
incursions began. At this point the strand fence was replaced with a combination fence.
Table 5. Evolution of electric strand wire fence design to try to exclude both foxes and badgers.
No. strands Height above ground (cm). Earth strands shaded
Greylake Design 1 10 5 10 15 20 30 40 50 70 90 110
Greylake Design 2 12 5 10 15 20 30 40 50 60 70 80 95 110
Alternative high tensile fence design for foxes
Gallagher recognise that foxes are very difficult to keep out indefinitely. They now recommend a
high tensile system comprising two fences as a ‘permanent solution offering optimum security
against foxes’: https://www.gallagher.eu/en_at/high-tensile-fence-foxes
56
The interior fence is a 5-wire Insultimber system consisting of fixed droppers at 40m spacings to
keep the fence lines correctly spaced and separated between non-fixed fence posts at 10m spacing.
Insultimber is a unique solution for electric fence installations as it is self-isolating, doesn't require
any chemical treatment or insulators, using simple clips to secure the fence line. The suppliers claim
that this system will easily last 20 to 25 years. However, as the bottom wire is close to the ground, it
is essential that the fence energiser is sufficiently powerful to burn off low vegetation (see here).
The exterior fence offers an extra barrier against foxes. It is a simple high tensile fence with a short
post of 1m, at a depth of about 50cm below the surface. The wires are spaced at 20cm and 45cm
above the ground.
Gallagher also recommend adding a Fox Light to the fence. The Fox Light comprises nine LED lights
which flash randomly at night to fool foxes into thinking that someone is patrolling the area (see
here).
Installation A certain degree of fencing skill is required, not only for installation, but also for the general upkeep
of electric strand fences. The best advice is to contact a specialist fencing company once you have
decided on a semi-permanent electric strand fence to advise on its design and specification. At most
reserves, the electric strand fencing was supplied and installed by a commercial firm e.g. Rappa or
Gallagher. At Ynys-hir, it took Rappa 2 to 3 days to put up 1.5km of fencing once the main corner
posts were in place. At another site, to save money installation was undertaken by reserve staff,
following a demonstration visit by a Rappa representative. It took 100 hours of paid staff time to
install 4.5km of fencing (plus the time for a volunteer to attach 9000 insulators to the posts). At
Greylake, the fence (c.3km) was removed and re-installed every year because the site floods
extensively in winter. In the first year of operation this took 459 hours (57 person-days) of staff
time. In subsequent years a supervised team of five volunteers were able to put up the fence in two
weeks (50 person days).
For successful installation the land surface needs to be reasonably flat otherwise the fence cannot
be made to run close to the ground. To overcome this, the spacing between fence posts can be
reduced or at one site chicken wire was attached to the lowest wire (earth) to fill in the gap to the
ground. Where the wire met the ground it was folded outwards and pegged down to form an apron.
On reasonably flat ground the spacing between the metal supporting posts with insulators can be 6-
7m. Railway sleepers or 9’ straining posts should be used at the corners or even every 100m of
fence in soft, peaty ground. At most sites, multi-stranded polywire has gradually been replaced with
high-tensile steel wire, which is less prone to breaking.
Usually, non-electrified gates are used for machinery access into the fenced area. This is a problem
as gates are the weak points for predator entry and so their number should always be kept to the
absolute minimum. To make them more fox-proof, the gates should be meshed with an additional
outward facing mesh overhang above the gate (see later). Sleepers or a layer of stone should be let
into the ground beneath the fence to stop predators getting under the fence. Additional mesh wire
overhangs should be put around corner posts or where the electric fencing passes through adjacent
57
fences. At Greylake a fox was seen to climb adjacent fencing and then jump over the electrified
fence.
The visual impact of strand fences is very low, even if the insulators are bright yellow (Fig. 18a).
However, it is better to specify black insulators and dull-coloured posts (Fig. 18b).
Fig. 18. Semi-permanent strand fences against foxes at (a) Ynys-hir (b) Ouse Washes Pilot Project
(now replaced by a combination fence).
If practicable, space should be left to allow vehicle access around the whole fence perimeter, which
reduces the time needed to check and maintain the fence.
Operation Wherever possible, it is best to use a mains powered energiser to run electrical strand fences.
Running costs are low (unlikely to exceed £20pa) and there are no batteries to go flat or replace.
The energiser specification required depends on the fence length but should be not less than 1.4
joules stored energy producing c.7000-8000V pulses of electrical current along the fence line. As the
bottom live wire is close to the ground it is important that the energizer is sufficiently powerful to
scorch away the vegetation in order to maintain optimum electrical conductivity.
If no convenient mains power source is available, the energiser can be battery powered. At Greylake
a 12v Wet Battery Energiser unit gave an output of 5000 volts that was sufficient to power c.3km of
wire. The batteries were changed every two weeks and re-charged back at the work centre with a
mains charger. The interval between re-charges can be increased by the use of a solar panel to
'trickle charge' the 12v electric fence battery. If the fence voltage is too low or to operate longer
fence lengths, the system should be divided into two and a second energiser used. (NB. For safety
reasons, two energisers should never be attached to a single length of fence!)
Earthing may be a problem on dry sites. The earth system should also be tested regularly to ensure
a maximum of 400 volts. If greater than this, add more earth stakes until it is brought down. As a
rule of thumb, there should be c.1m of earth rods per joule of energizer output.
Generally, electric strand fences are electrified 24 hours per day all year round. At some sites no
wader chicks have been found harmed or killed by the fence, even though they move regularly
a) b)
58
between feeding areas inside and outside the fence e.g. at Ynys-hir. However, rarely wader chicks
have been found dead beneath electric fences, so at some sites the lower electrified wire is turned
off when wader chicks are likely to want to feed outside the fence. At Greylake this was once the
first nest has hatched, at the Ouse Washes not until the first wader chicks were nearing fledging.
Maintenance Much time and effort is required to keep a semi-permanent electric strand fence running effectively.
Regular maintenance visits are essential to keep sufficient tension in the wires and to prevent wires
shorting on vegetation, which requires mowing, grazing or the use of herbicides.
At most sites the whole fence is checked over several times a year to make sure that all the wires are
tight and that the insulators are attached correctly. At some sites the wires have to be tightened
frequently, because the peat soil is so soft that the metal posts lean over causing the wires to sag.
Sometimes whole sections of fence have to be moved away from ditch edges of because of
fluctuating water levels. Fortunately, it is relatively simple to move sections of the fence around.
Other problems encountered are cracked insulators that have to be replaced (usually from about 6-7
years after installation) or insulators slipping down the stakes, which causes the wires to sag.
Vegetation control has to be undertaken regularly at most sites. This normally involves applying
herbicide (usually Roundup®) 3 - 6 times between the end of March and October. At the Ouse
Washes each application took 3 man hours for the 4.2km fence-line using an ATV. Once a year, 2m
strips are mown alongside the fence-line to remove excess vegetation (e.g. nettles) to prevent them
from falling down on to the wires. At Greylake the fence line vegetation was brushcut once initially
and a second time later in the season. It was also sprayed three times per season with Roundup®
applied with a knapsack sprayer. In total vegetation control took around 32 man-hours per season
for the 3km fence.
By contrast, at Ynys-hir no herbicide is used as the whole area containing the fenced enclosure is
grazed all year round at different times by sheep and cattle. For areas that sheep cannot reach to
graze, e.g. along track/path sides and near ditches, the vegetation beneath the fence is mown or
strimmed. It is relatively easy to adjust or move a section of fence to strim underneath it.
Monitoring The entire fence line should be walked weekly to check for problems just prior to and during the
early part of the breeding season and then less frequently as the season progresses. The check
should ensure that: 1) the structure is maintained to the required specification; 2) vegetation is not
touching the fence.
Voltage checks to ensure that the fence voltage is at the required level should be made frequently
during the breeding season. At most sites this should be done daily, testing each fence section in
turn. Twice per week should be the absolute minimum. If the voltage is found to be low then it best
to use a fault locator to indicate the direction of the fault, otherwise it can take hours to locate the
problem.
Outside the breeding season, the power supply to the fence should be checked about once a month
with a voltage tester to ensure that it is above the absolute minimum (4000 volts) at all points on the
59
fence line. If lower than this it must be improved or the predator will not get a high enough shock to
learn to respect the fence. The earth system should also be tested regularly to ensure a maximum of
400 volts. If it is greater than this more earth stakes should be added until it is brought down.
Systems are also available to monitor fence performance remotely. GSM Smart Phone Control
Energisers will send alerts to a mobile phone if there is a significant drop in fence or energizer
performance (you can set your own threshold for low voltage warnings). A status report can be
obtained any time via SMS sent to the smart phone (fence voltage, energiser on/off etc.).
The area within the fence should be monitored for foxes or other predators by looking for signs e.g.
scats or footprints (see below), scanning at night with a lamp or thermal imager or by installing trail
cameras.
Fig. 19. Foot prints showing that a fox jumped over (left) or got under (right) a strand electric fence
Problems At several sites, hedgehogs and frogs have died from multiple shocks from electric strand fox
fencing. Hedgehogs are a particular problem because they tend to roll into a ball when shocked
rather than to move away. To prevent electrocutions, a low physical barrier can be installed in front
of the electric fence or, in extremis, the bottom live fence wire can be disconnected. At the Ouse
Washes, the problem was solved by installing a length of plastic barrier mesh netting cut in half
along the section of the fence-line where the hedgehog casualties had occurred.
60
At three sites, mute swans died having hit or become caught in the fence. At one site, a section of
fence was knocked over on a number of occasions, probably by deer or badgers. To reduce bird
strike risk or to deter deer from trying to jump over, the top strand can be marked at intervals with
twists of white electrical insulating tape (see Fig. 14).
Effectiveness of electric strand fences at excluding predators There is little published information on the effectiveness of electric strand fences against predators.
Poole & McKillop (2002) tested the standard 8 strand specification for strained wire electric fence
against captive foxes (McKillop et al., 1999). The fence was crossed only when the foxes were under
the greatest stress (when people were inside the enclosure).
An early analysis (Malpas et al. 2013) suggested that lapwing nesting success was significantly lower
within electric strand fences than within combination fences (69% hatching success compared to
90%). However, there is a general agreement amongst site managers that the standard eight strand
fences (or 9 strand wire with an additional earth wire added to the bottom to prevent animals from
digging underneath the fence) can be effective at excluding foxes in the wild. At the Ouse Washes,
in the first few years of operation, only one fox entered the fenced plot (via a non-electrified gate),
although there were many foxes in the surrounding area. However, in subsequent years foxes began
getting over and under the fence (Fig. 19). At another site, there was occasional evidence of foxes
inside the fence that had apparently gained access by digging under it.
Providing the recommendations above are followed with regard to the use of a suitable energiser
and power supply to maintain the required voltage and high tensile steel wires rather than polywire,
the standard four strand electrified wire fence against badgers seems to be effective at reducing
incursions and reducing the damage badgers cause, at least initially.
The effectiveness of semi-permanent electric strand fences appears to be particularly compromised
at sites where a hybrid fence design is used to try to exclude both badgers and foxes from the same
area (even though some of the fox incursions are via non-electrified gates). At Greylake the
stranded fence worked against foxes and badgers for a number of years. However, once badger
incursions started they began to force their way through the wire strands. Adding a wire apron at
the base of the fence to deter digging underneath did nothing to keep them out.
In summary, strand fences can exclude foxes and badgers, sometimes for a number of years, but in
the end the attraction of the food source inside the fence seems to be so great that badgers in
particular overcome their fear of the fence and force their way through it. At such sites a
combination fence is probably the better long term, albeit more expensive, option. Strand fences
do have a role but probably mainly for short term/rotational installations (see below).
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Chapter 7. Temporary electric fences By definition temporary fences need to be quick and easy to install and take down. For this reason,
the type of multi-strand electric fences described above, enclosing up to 50ha are normally
described as ‘semi-permanent’, rather than ‘temporary’, even though at one site (RSPB Greylake) a
3km fence used to be taken down and re-installed every year.
Situations where the use of temporary electric fences is appropriate Temporary electric anti-predator fencing is the best option for sites where fencing cannot be left out
all year e.g. at sites subject to regular seasonal flooding, or where fencing requires re-locating
frequently e.g. where the target species moves around between or even within seasons. Temporary
electric fencing is usually intended to exclude foxes and sometimes badgers. The effectiveness of
electric fences against foxes and badgers seems to decrease over time, even if very effective initially.
However, to be worthwhile, temporary fences usually only need to deter predators for a short
period of time before the fence can be removed for another year (6-8 weeks to protect breeding
waders of wet grassland to increase their productivity). As they can be moved around they can
protect the best area in any particular year i.e. they can follow the target species around (or even
vice versa).
Temporary electric anti-predator fencing is especially useful where the target species can be
protected by a comparatively short length of fencing enclosing a small area, and where the fence can
be erected easily. Ideally the fence should be installed before breeding starts, but if this is not
feasible, the fence must be capable of being erected very quickly with minimal disturbance to the
bird(s). In most cases this means that the fenced area has to be small. For some target species
installing the fence will require a disturbance licence.
Situations where the use of temporary electric fences is appropriate include:
- To protect individual nests of stone-curlews breeding on rotational fallow plots in grassland
or arable where combination fencing is not practicable but where mammalian predation is
causing low productivity (<0.61 chicks per pair). The fence can even be installed after the
birds have laid (see later).
- To protect seabird breeding colonies, especially terns, where the birds nest in very close
proximity to each other.
- One-off breeding attempts of other rare ground nesters e.g. black-winged stilt with the
fence installed after the birds have laid.
Another potential use for temporary electric strand fencing is to reduce the prey ‘hot spot’ effect
sometimes associated with permanent fencing. Although semi-permanent fences intended to
increase the productivity of breeding wet grassland waders usually work well, they can create a
temporary prey ‘hot spot’, making wader chicks more vulnerable to predation from aerial predators.
The chances of this occurring might be reduced by employing temporary/portable electrified wire
strand fences as well as, or even instead of, permanent predator exclusion fencing. This would
enable ‘the protection’ to be moved around a site between years, installing it in a different location
each year. Experience at RSPB Greylake (see above) suggests that it is feasible to install a 3km 9
strand electric fence afresh each year enclosing up to at least 50ha of wader nesting and feeding
habitat. Fences with even fewer strands can be installed rapidly and can be effective for short
periods (see below).
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Siting Temporary electric fencing must not be used on scheduled historic and archaeological sites, without
specialist approval. Fencing must not impede rights of way and there must be no
blocking/restriction of access to CRoW land without a derogation from NE to exclude public from a
fenced off area. Note that the need to provide a point of access could be a non-electrified self-
closing gate, but this would need to be made predator proof. Such gates are employed by RSPB at
temporarily fenced grazing plots in Dunwich Forest (A. Needle pers comm.).
Types of temporary/portable electric fences There are two types, either:
Strained wire (strand) fences. A series of electrified parallel conducting wires at varying heights
above the ground made from either polythene twine interwoven with steel strands (polywire) or
galvanised steel. Because of the ease of installation, many temporary fences utilise polywire rather
than steel wires (but see here). Also, polywire is cheaper to purchase but is a poorer conductor than
galvanised steel wire. Polywire can be supported by lightweight plastic polystakes (rather than
wooden or metal posts). Both steel and polywire strands can be wound onto reels for easy transport
but galvanized steel is much heavier.
Or:
Electrified netting fences. These consist of a heavy-duty, polythene twine mesh in which the
horizontal strands are interwoven with electrically conductive stainless steel wire supported by
vertical strands of plain polythene twine or flexible plastic (as in some goat fencing). Fences vary in
height and mesh size, depending on the manufacturer, and come in rolls fitted with spiked plastic or
fibreglass supporting posts built into the fencing at regular intervals (c.3m) with a clip at each end to
join rolls together. Although self-supporting in straight runs, they usually need wooden supporting
posts at turns or corners. Even so, these fences are very easy and quick to erect and dismantle e.g.
they can be re-used at a different location within the same season (e.g. re-lays or second broods of
stone curlews).
Netting is only suitable for protecting small areas (Rappa Fencing Ltd) and should not be used when
hedgehogs are present. The bottom wire is not electrified and can be bitten through by rabbits. A
strained-wire design offers advantages over netting in terms of durability and versatility. It also
carries a higher voltage than netting and can be less damaging to other wildlife, such as hedgehogs
and amphibians which can become entangled within mesh fences and killed as a consequence.
Temporary strand fences Specification The basic design principles for temporary electric strand fencing match those for semi-permanent
strand fencing. The difference is that the fence lengths are usually much shorter enclosing
comparatively small areas, enabling fences to be assembled and dismantled every year. For longer
fence lengths the number of strands/fence height is reduced to make the fence quicker to install,
working on the premise that foxes in particular can initially be very wary of electric fences and so the
fence will provide some short term protection, even though it will be less effective at keeping
predators out generally. Both the fence and power source should be removed as soon as possible
after the fence is no longer required so that predators do not get used to penetrating the fence.
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Standard configurations for strand fences Most RSPB reserves installing anti-predator fencing for a season employ the standard 9 strand (5
live, 4 earth) Rappa design for semi-permanent electric strand fencing. At RSPB Minsmere such
temporary strand electric fencing has been used since 2003 to surround 1.5ha ploughed plots to
protect individual pairs of nesting stone curlews from fox predation. Anti-predator temporary
electric strand fencing is also an option in NE’s new Countryside Stewardship grant scheme to
increase the productivity of priority ground-nesting birds in three defined situations:
• On habitats within grassland and arable used by breeding stone-curlew, where combination
fencing is not possible (e.g. around rotational fallow plots).
• On certain coastal habitats (e.g. shingle) used by breeding seabirds, especially terns.
• On lowland wet grassland used by breeding waders where permanent combination fence cannot
be used for practical reasons e.g. periodic flooding.
The specifications for the two main temporary fence types are shown in Table 6. The Minsmere
fence is the basic Rappa design, adjusted slightly to match the 92cm polystakes used to support the
fence (see below) and with the addition of a higher white polytape line to deter red deer from
jumping the fence (Fig. 20) when there is more to eat inside than outside. Deer also seem to like
lying on the bare, cultivated soil of stone curlew plots. (Note the reserve has just begun using
polybraid as it is less prone to wind resistance and stretching than polytape, and the deer still seem
to be deterred by it.). The lowest wire is an earth as it is impossible to maintain as live because of
vegetation growth.
Table 6. Strand spacing for temporary fences as specified in NE’s new Countryside Stewardship
grant scheme and as used to protect stone curlews at RSPB Minsmere, compared with the
two standard ‘semi-permanent’ strand configurations
Fence Strands Strand spacing (cm). Earth wires shaded.
NE 12 5 15 25 35 45 55 65 75 85 95 110 150*
Minsmere 9 9 18 28 38 50 63 76 90 105*
Defra 8 5 15 25 35 45 60 80 105
Rappa 9 5 13 20 28 38 50 66 84 105
*An extra wire of white polytape (multi-strand) is added above the fence to increase visibility to
birds and deer.
At Minsmere the strands are supported by standard Rappa 92cm polystakes (as in Fig. 20 below) or
on slightly taller steel stakes with separate screw together insulators that can be set at whatever
spacing suits. However, these are heavy and the insulators can move if loose.
Installation If possible the fence should be erected before breeding starts. If it is not, the fence will need to be
installed with minimal disturbance to the birds. A disturbance licence will be needed from the
Statutory Agencies for Schedule 1 species, such as stone-curlew and little tern.
Installation can be speeded up if a proprietary winder (e.g. ATV Winder from Rappa powered from
the back tyre of an ATV) is used to erect and dismantle fencing. This can carry up to 600m of stakes
and wire in one go. Also, this means that galvanised electric fencing wire is as easy to utilise as
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polywire. For example, Vidoflex 9 (sold by Gallagher) is made for winding regularly and will not twist
or kink and is resistant to stretching and so is ideal for long portable fences. It is claimed to have 40
times better conduction and is over 50% stronger than regular polywire.
At Minsmere a fence is usually only erected when stone curlews are definitely nesting on a plot and
is not taken down again until later in the year. However, as stone curlews are fairly site faithful,
sometimes staff gamble and erect a fence around a favoured plot prior to the stone curlews settling.
To minimise disturbance if the birds are already present, the corner posts are fixed first as a separate
operation, otherwise fence installation takes too long. The length of time to install the corner posts
(150mm fence strainer posts) depends on the technique employed; using a post hole borer, about
an hour, a bit less with a Metpost Post Support driven into the ground to accept a (square) post.
Even though they are let into the ground, corner posts often require in addition guy ropes to
maintain sufficient tension in the fence.
Once installed, corner posts are left in situ from year to year around each plot. At Minsmere, all the
traditionally used stone curlew plots, plus one or two that have not been used have permanent
corner posts (150mm fence strainer posts) in place. Current practice is to install these upside down
to prevent crows from perching on them – sometimes with a protruding nail driven into the point to
further reduce the opportunity for crows to perch. Any corner posts installed conventionally (i.e. the
right way up) are fitted with plastic anti-pigeon spikes (pigeon floppies) to stop crows or kestrels
perching on them.
Some of the posts have conventional plastic insulators, whereas others have twin wall water pipes
around them as a convenient alternative that avoids having to use multiple screw-in insulators (see
Fig. 20).
Fig. 20. Temporary electric strand fence at Minsmere: a) length of twin wall water pipe fitted over a corner post instead of separate insulators; b) Rappa 92mm polystake and reel of white polytape (now replaced by polybraid).
a) b)
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The Minsmere reserve staff are experienced at erecting fencing and depending on how much
`gardening’ is required, it takes two people only 1.5 - 2 hours to install the fence working
methodically once the corner posts are in place. Fences are installed with a Rappa ATV winder
http://www.rappa.co.uk/products/7-atv-winder, which can handle four strands at once. The ninth
(deer deterrent) wire is usually dispensed by hand for speed of installation. The four earthed wires
are put out first, and then the process is repeated with the four live wires. The wires are supported
by 92cm polystakes put in every 10m. Separate 135cm long horse polystakes are used to support
the higher (ninth) polytape/polybraid strand. Experience has shown that if more than 2 or possibly 3
people are involved, they work less methodically and the fence actually takes longer to install! It
takes less time to take the fence down at the end of the season.
Rappa also sell hand reel kits to speed up the installation of strand electric fences. These are
handles and knobs that attach to the reels so that they can be unwound/wound individually by hand
if a mechanical mounted or trailed winding machine is not available or where its use is not
practicable e.g. the shingle beach at Kessingland where NE will not allow the use of an ATV to fence
the little tern colony. The hand reels are used in conjunction with special metal `finish posts’ that
have hooks to which the hand reels attach, instead of horizontal bars to mount the reels on (see
below, Fig. 21). In practice hand reels are a challenge to use if loaded with a long length of steel wire
as they increase weight substantially compared with polywire - especially if winding it in whilst
walking on shingle (A. Needle pers comm.) A half way measure would be a Rappa barrow winder,
but this too would be a struggle to push on shingle.
Operation The Minsmere fence energiser is powered by 12v deep-cycle batteries and operates at ~7000V. A
complementary solar panel unit is available, enabling the same battery to last the whole season.
Good earthing is extremely important because the soil can dry out. To counteract this several
points around the fence are earthed (see here).
Maintenance Lack of regular maintenance is the main cause of fence failure. Regular visits should be undertaken
during the breeding season to ensure that the structure is maintained to the required specification.
Strong winds can cause polytape to stretch and sag, and loosen the stakes in the ground causing
them to lean, so tightening of wires or replanting of stakes is sometimes required. Any vegetation
that is touching or getting close to touching the bottom live wire must be removed or controlled. At
Minsmere, rabbits keep the grass extremely low (but not nettles, thistles, ragwort and bramble),
reducing the amount of vegetation management required. Any stray nettles, ragwort etc. are
removed by hand. NE recommends initially strimming under the fence line and then applying
herbicide (with repeat applications as necessary). Note that for some target species, any
practitioner(s) involved with these processes must hold the appropriate disturbance licence.
Monitoring For ‘temporary’ anti-predator fences funded under the new Countryside Stewardship Scheme,
Natural England require regular inspections at specified intervals (usually at least once a week when
birds are nesting). These are needed to ensure that:
• vegetation is not touching the fence
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• the voltage is at the required level
• the structure is maintained to the required specification
• no target predators are in the enclosed area
At Minsmere the general area around a fence is checked regularly for the presence of foxes in the
early morning and evening.
Effectiveness There have been only two known incidences of foxes getting inside a strand fenced plot at
Minsmere. Adult stone curlews move through the fence easily and no chicks or non-target species
have been found killed or harmed because of the fence.
Problems encountered with the Minsmere fences Initially, the fence has a fairly high visual impact because is surrounds such a small area. However, it
quickly becomes less visible as the polywire loses its brightness. Red deer then appear not to be
able to see the strands and damage the fence by running into it. This problem has been solved by
adding an extra strand consisting of white polytape or polybraid to make the fence more visible to
the deer.
Berney Marshes case study (Jim Rowe and Mark Smart) At Berney, foxes are controlled up to 2-3 times per week from December to June. In addition, in
2017 temporary electric strand anti-predator fencing was trialled as part of a UEA/RSPB
experimental study of breeding waders. In mid-March, electric fences comprising eight alternating
live and earth galvanised wire strands were installed to protect c25ha comprising eight wet
grassland plots from predation by large mammalian predators. Individual fences were up to 1600m
long. Given the model of energiser used (see below), and the likelihood of wires shorting out on the
growing vegetation, the voltage would be insufficient for fences any longer than this.
The sites were chosen on the basis of the previous distribution of wader nests and the ease of
installing the fence. Installation took five person days per fence, two for culverting footdrains where
they crossed the line of a fence, three for the fence itself. This was with a very experienced team
using an ATV fence winder).
The fences were powered by Speedrite S500 0.5 joule integrated solar powered energisers backed
up with standard 12v batteries. The longer fence lines were split into two, each with their own
energiser to maintain good fence performance.
Two gateways were incorporated into each plot (Fig. 20) to enable plots to be grazed lightly if
necessary. Plots were not grazed while they contained active nests and sufficient chick rearing
habitat. The gateways were clever electrified versions of ‘Australian gates’. Eight strands of
polywire were used to the bridge each gateway. The strands were connected to a moveable fence
post that could be inserted into a loop of wire attached to the bottom of a fixed post knocked into
the ground. A second loop of wire at the top of the fixed post could be slipped over the top of post
with the wires
The grass below the fence was not managed. As the vegetation grew, the bottom two wires were
switched off to prevent shorting out, with the next strand above now being the lowest live wire.
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Over 50 lapwing and redshank nests were monitored within the fenced areas and by the end of May
their survival was close to 100%; higher than that of nests outside the fenced area.
Fig. 21. An electrified polywire ‘Australian’ gate at RSPB Berney. Note the metal `finish posts’ to
which the individual wire strand reels hook onto.
Brading Marshes Case Study (Keith Ballard) In 2016, a standard 9-strand Rappa anti-predator fence (5 live, 4 earth strands but with 70mm
spacing of the bottom 5 wires) was erected on 1 April in one continuous 1km loop (i.e. no gates)
around 5.5ha of the best lapwing nesting habitat. It was dismantled on 3 June. No grazing took
place while the fence was in place but the area was grazed before and afterwards. The fence took
three people one day to put up but only half a day to take down. A Rappa ATV fence winder on a
quad bike was used for reeling the wire in and out. The vegetation under the bottom live wire was
killed by spraying with glyphosate. The fence voltage was checked daily to ensure a consistent 7000
volts throughout. The batteries were changed twice weekly. Some short circuiting around plastic
insulators on metal posts was experienced on one damp day after winds, thought to be caused by
salt deposition.
Lapwings nesting inside the fence were checked daily to establish if nests were still present. In total
there were nine known nests of which seven were seen to hatch successfully; the outcome of the
other two nests was inconclusive. It was believed that some chicks were soon predated (predator
unknown) and most broods were moved from the fenced area into neighbouring fields with better
cover. It was concluded that the fencing had a positive effect on nest success but the effect on
productivity was inconclusive.
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Other temporary electric strand fence configurations Foxes can be wary of electric fencing, with relatively low fences deterring the majority of foxes in
some situations. This makes it feasible to protect larger areas for fox predation or to erect rapidly a
fence around a nesting colony of the target species. Most fences of this type have 2, 3 or 4 live
strands.
Two strand fences In the Netherlands, 2 strand fences are employed immediately adjacent to ditches to protect wet
grassland with breeding waders (J. Smart pers comm.). Foxes have to swim across ditches to access
the area and as their fur is wet when they encounter the fence, they are more likely to receive a
shock making the fence more effective.
To deter badgers temporarily, two strands of electrified 'polywire' placed at 7.5 and 20cm above
ground level have also proved effective. Even one electrified strand at nose level can be effective at
deterring badgers and may be useful as a temporary deterrent. It is important to ensure that no
vegetation touches the wire(s) to prevent it shorting out.
A simple two strand fence forms part of a temporary fence solution to keep out foxes (see below).
The fence comprises short fence posts of 75cm with two Vidoflex 9 wires at 20cm and 45cm above
ground.
Three strand fences In this configuration, the first wire is usually at c.15cm, low enough to deter a fox from trying to dig
underneath without it being shorted out by vegetation with the middle strand at fox nose height
(c.30cm or around knee height).
On the Sands of Forvie National Nature Reserve, Aberdeenshire, Scotland, a low electric fence was
tested as a barrier to foxes preying on sandwich terns and eiders (Patterson 1977). In 1974-76 a
2200m electric fence was erected across a spit. The fence comprised three parallel steel wires
spaced 15 cm apart, the lowest 15 cm above the ground. The wires were supported by nylon
insulators on steel posts (spacing between posts varied from about 6m on level terrain to 3m on
rough ground). It was charged by one 'Koltek Big Tom' fencer unit per 1000m of fence. The fence
could not be extended onto the intertidal area at either end as it would be short-circuited at each
high tide. The fence was removed in August when breeding had finished.
No fence crossings were recorded in 1974. In 1975 there were five fence crossings all of which
appeared attributable to one individual. It jumped the fence on 21 February (three days after fence
erection) and walked through the wires on 24 and 25 February. The main weakness was that some
foxes bypassed the fence via the intertidal areas: of 28 tracks on the beach, 16 (57%) passed directly
along the shore, the remainder first encountered the fence then moved along and around an end.
Overall, the author concluded that the electric fence, although not fox-proof, was an effective
deterrent reducing fox visits to the general area by over two-thirds and turning back about 60% of
those which did try to visit. Fox activity beyond the fence was thus reduced to about 16% of that
expected without the fence. Crossing of the fence was rare (6% of encounters) but foxes were able
to pass round the ends of the fence on unprotected intertidal areas. Where this became common
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and predictable it enabled selective removal of an individual fox causing damage, since the fence
steered the animal to a predictable place.
A similar fence was used to protect a least tern colony (Sterna a. albifrons) from fox predation at
Cape Cod National Seashore in Massachusetts, USA (Minsky 1980). On 24 June 1978, over one mile
(1.6km) of electric fence was erected around the perimeter of a least tern colony The fence
comprised three strands of wire, 6 inches (roughly 15cm), 12 inches and 18 inches above the sand,
connected to a 6 volt battery-operated energiser with an 8 foot (about 2.4 m) copper ground rod.
The fence was taken down on 27 August.
The number of tern nests fell from 138 on 20 June to 45 on 23 June, prior to the installation of the
electric fence, and fox tracks were found criss-crossing the colony. Following the erection of the
fence, the number of nests increased to 85 by 6 July, and although fox tracks were found near the
colony, they were not recorded closer than 10 feet (roughly 3 m) from the fence. Even when the
fence was turned off for a week, it still deterred the foxes. None of the 15 or so new nests initiated
outside the electric fence survived. The author concluded that there would have been virtually no
tern productivity that year without the fence.
Four strand fences
Mobile fencing against foxes Rappa sell a four (and six) strand fence for use against otters (Fig. 22). However, as it utilises very
strong, seven-strand galvanised steel wire it should be effective against badgers as well. The wire is
supported on 80cm galvanised steel electric fencing stakes, with a double spike for easy penetration
into hard ground. Bespoke steel stake insulators enable the wire heights to be set optimally for each
situation/predator. The fence could probably be installed and dismantled with an ATV Winder.
The metal stakes are also available in 90cm and 120cm versions, which can take six strands if four
proves to be insufficient. This would enable extra wires to be installed to make it more effective
against foxes. Unfortunately, the corner anchor stakes supplied with the fence are only 50cm long
with four insulators. However, it should be possible to source a suitable metal alternative from
another company or to use longer wooden posts for the corners and where the fence changes
direction.
Temporary 4 strand fencing (7 strand galvanised electric fencing wire) with metal intermediate posts
is also employed by MoD to protect stone curlew plots in Wiltshire.
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Fig. 22. Rappa 4 wire strand fence designed to exclude otters.
Gallagher sell a permanent strand fence to keep out foxes, employing separate inner and outer high
tensile fences (https://www.gallagher.eu/en_gb/high-tensile-fence-foxes ). This design can be
adapted to provide a temporary fence installation to provide protection from foxes. The inner fence
is a SmartFence, an instant all-in-one portable 5-wire system with posts, reels and wires that is very
quick to install. The system is 100 metres long (10 posts), and is suitable for uneven terrain. It can
be connected to any energizer for instant electric fence protection. This type of system makes fence
installation very fast, especially on soft ground. The spacing of the wires is fixed, but it is possible
that the system could be adapted so that the spacing could be varied.
For an extra barrier against foxes, Gallagher recommend installing a second simple two strand
exterior fence outside the main fence (https://www.gallagher.eu/en_gb/high-tensile-fence-foxes).
Case studies For the five years prior to 2017, a 4 strand standard stock electric fence has been installed in March
around the Allen Pool at Leighton Moss to keep foxes out to protect nesting avocets and black-
headed gulls. The wires are supported on standard cattle electric fence posts, with wires in notches
2, 4, 7 and top (i.e. about 20, 40, 75 and 85cm above ground level). The fence takes a day to install
(600m) and is removed after the end of each breeding season.
In the first few years of installation the fence appeared to keep out foxes effectively, as avocet
hatching success was high. However, the fence seems to have become gradually less effective over
time. In 2016, the fifth year of operation, at least one fox was seen to get through the fence in spite
of being (visibly) shocked. It is planned to install a more robust fence in future years.
In 2016, a temporary 4-strand fence was installed at Pulborough. The bottom two wires were
spaced at 10cm and the top two spaced at 15cm, giving a total fence height of 50cm.
In March 2017 a four strand temporary electric fence was installed alongside ditches at the Nene
Washes to protect two areas with nesting black-tailed godwits from predation by foxes and badgers
(Fig. 23). One fence was 1.6km long and the other 2.0km. The fences were powered by a 12J
battery powered energiser and the battery was kept charged by a 10W solar panel. The fence is
positioned within the ditch so foxes and badgers have to swim up to the wires. The bottom strand is
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an earth about 5cm above the water surface with three live wires above at 10cm intervals. Where
the fence crosses a ditch, the ditch is filled with sheep netting hung on plain wire
Fig. 23. Temporary four strand electrified fence along a ditch at the Nene Washes prior to and after
raising the water level.
The fences were dismantled on 5 and 13 June. This took two people 14 hours. The process was made slower by the need to remove by hand the vegetation adhering to the bottom wire. Without this, fence removal would have taken less than two days.
Foxes twice managed to penetrate the 1.6km fence. The first was when the fence was ‘down’ as a result of an increase in ditch water levels and the second when the voltage was very low. This resulted in a vixen being trapped within the fence. It was shot the next day, but not before the loss of some wader nests and some wader chicks, which were found cached.
The 2km fence had one fox intrusion. A fox pushed its way through the fence when the voltage was not that low (5.5kv). However, this coincided with a period when many nests were hatching and young chicks starting to move around, which may have provided the extra motivation for the fox to push through the fence. The intrusion resulted in the loss of two nests and two godwit chicks in the early hours of the morning. The fox was shot the following night as it paced up and down the fence perimeter. There were no badger intrusions.
It is important to monitor fence voltage and for the presence of foxes within the fence. However,
care should be taken when raising the fence voltage to make sure there is no fox inside. A fox
trapped inside the fence seems to result in disproportionately high rate of predation.
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In summary, the fences appeared to work well, with only three recorded fox intrusions between 11
April and when the fences were removed (5 June and 13 June respectively). Nest loss to mammals
was only recorded during the periods of known fox intrusion. Daily survival rate of wader nests
within the fenced areas was significantly higher (about 2.5x) than in the adjacent unfenced areas
(Mark Whiffin pers comm.).
Summary attributes of temporary <4 strand electric fencing (Table 7)
Live
Strands
Target Spacing (cm) To benefit Effective
for?
Reference
2 Badger 7.5, 20 ? ?
2 Fox ? Dutch grassland waders ? J. Smart pers. comm.
2 Fox 20,45 ? ? Gallagher
3 Fox 15,30,45 Terns > 6 months Patterson (1977)
3 Fox 15,30,45 Least tern > 2 months Minsky (1980)
4 Fox 20,40,75,85 Avocets, bh gulls > 5 months R. Miller pers comm.
4 Otter ? Fish ? Rappa
Electrified mesh netting There is not much published information on the use of electrified mesh netting to exclude predators
for bird conservation reasons. Lightweight electric poultry netting is claimed to be highly effective at
excluding foxes, at least for short periods. Therefore, it has the potential to protect individual nests
from predation by foxes (but it is not recommended to protect against badgers), even though
netting is only suitable for protecting small areas (Rappa Fencing Ltd). Note: Never use electrified
netting where horned animals could become entangled as it can cause great distress to the animal.
Similarly, electrified netting should not be used where hedgehogs are likely to encounter them.
Electric mesh netting is very forgiving, adapts easily to slopes and dips in the ground and is very easy
to erect, at least where the netting supporting posts can be pushed into the ground easily - simply
unroll the net and then tread in each post. It is just as easy to dismantle, bundle up and re-erect
elsewhere. Agrisellex claim that 145cm will prevent all foxes from jumping over it. It is relatively
cheap; 1220mm high, 7.5cm x 5cm mesh netting costs c.£177 per 50m (Electric Fencing Company).
The netting is made of polythene and stainless steel conducting twine and is erected with support
poles and ground spikes. 105cm, 122cm or 145cm high netting is available in 50m lengths with posts
built into the net. Nets can be linked together to create different sizes of enclosure. The netting can
be green, black or orange. To be sure of excluding foxes the mesh size needs to be a minimum of
7.5cm. However, some companies supply ‘poultry netting’ where the bottom few horizontal strands
are even closer together (5cm, Fig. 24), which wader chicks might not be able to pass through, or
‘sheep netting’ where the horizontal strands are 10 or 15cm apart. Double pronged netting
supporting posts are stronger than single ones making the netting less prone to sagging. The posts
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should be about 3.5 - 4m apart (Fig. 24), but additional posts may need to be added to support the
net if the land is very undulating. Ensure that corners are firm as the flexible posts will bend. It does
not need tensioning; to keep the net tight; either use the pegs and guy lines provided or anchor
corner posts to a fixed post or structure using plastic, non-conductive wire to prevent leaning over or
sagging. Alternatively, the standard electrified netting can be made more robust by weaving 3 non-
electrified strands of wire through the net. This can be tensioned to make the netting more taut
(Fig. 25).
Fig. 24. A typical specification for electrified poultry netting. Others are available.
Fig. 25. Electrified netting strengthened with horizontal wires protecting breeding little terns in N. Wales
Because nets are electrified through all the horizontal strands except the lowest (but not the vertical
ones), the ground must be kept free of tall vegetation as touching the electrified wires can short the
20cm
15cm
10cm
10cm
10cm
10cm
10cm
5cm
5cm 5cm 5cm 5cm
105cm
7.5
cm
7.5
cm
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fence and make it ineffective. It is important that the energiser has sufficient capacity to power the
net; a 12v battery energiser should have at least 0.5 stored joules energy per 50m of netting and it is
essential that the energiser acquired is capable of powering the maximum length of netting that
likely to be used in future. Netting cannot carry as high a voltage as stranded wire (Poole &
McKillop, 2002) and energisers greater than 4 joules should not be used because when the netting is
damp, arcing can occur across the wires. Where possible, the energiser should be placed in the
centre of the fence so that the current flows both ways.
When taking a net down, it is best not to roll it up at first - simply gather the posts together allowing
the netting to fold against itself. Then roll up the folds to meet the bundle of posts and secure them.
Potential problems Hedgehogs and deer may get entangled in the netting. Wader chicks might not be able to pass
through the mesh netting if too small. Radio tracked lapwing chicks had no problems crossing a
15cm diameter mesh fence (Schifferli et al., 2006), but this mesh size might not keep out a
determined fox. Both adult and chick stone curlews can pass through standard Flexinet poultry
netting. However, on two occasions in Suffolk, adult stone curlews became entangled in green
Flexinet fencing (see below).
Case studies At Minsmere, non-electrified orange Flexinet poultry netting 110cm high was used originally as a
secondary defence 30cm inside an electrified multi-strand fence around stone curlew nesting plots.
(NB. Non-electrified as it is illegal to have two electrified fences within two metres of each other.)
However, if left in-situ for any length of time, non-electrified Flexinet will be chewed through by
rabbits making subsequent use as electrified fencing impossible unless repaired first.
Electrified mesh netting has since been used to protect stone curlew nesting away from stone
curlew plots, either as a 0.25ha square (4 x 50m fence lengths) or as 6 lengths in a 2x1 rectangle to
enclose a bigger area. The fencing is very quick to erect and seems to be effective. Most losses here
have been (free-ranging) chicks rather than at the (fenced) egg stage.
At Minsmere, the stock of standard orange mesh fencing was supplemented with green fencing in
the expectation that it would appear more discrete. However, the `in-your-face’ green colour does
not match any natural vegetation in the UK and is very obvious when looked at end on. Although it
is less visible when viewed from the side, the same can be said of orange fencing. Furthermore, two
adult stone curlews (attending separate nests a couple of miles apart) became entangled in the
green netting. Probably coincidentally, this had never happened with orange fencing. Even so the
reserve has now reverted to using orange netting only.
At Minsmere, temporary mesh fences are effective at protecting stone curlew nests from fox
predation. In 2017, reports of a fox inside a mesh fence were the result of a fox gaining access via a
rabbit warren connected to a rabbit hole(s) running under the fence. Staff always consider this
possibility when installing a fence, but it is not easy to determine how far some rabbit holes run.
Battery powered poultry netting has been used to protect the little tern colony on shingle at Rye
Harbour. There have been no cases of electrocution. The visual intrusion of the fence was reduced
by specifying black fencing rather than the usual bright orange colour.
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In Germany, electrified netting is being used by NABU to protect individual curlew nests from ground
predators https://bergenhusen.nabu.de/forschung/wiesenvoegel/index.html. An information sheet
is available from Natalie Meyer ([email protected])
Curlew nests are enclosed within a 25m x 25m square of netting (Fig. 28). After the clutch is
complete, the four fence sections (100m of netting) and polystakes are laid on the ground in a
square around the nest as quickly as possible to get the birds used to the netting. If the bird does
not return to the nest within 90 minutes the fence material is removed. If everything seems OK, the
next day the corner posts are hammered in and each section of fence is tensioned and tied to the
posts with rope, the polystakes pushed into the ground and the bottom of the fence pegged down.
A battery-powered energiser is then connected to the fence to electrify it. Again, if the bird has not
returned to the nest within the next 90 minutes, the fence is laid down horizontally on the grass.
Car batteries are changed every 5-7 days. The grass around the fence is not strimmed because of
lack of time. The electricity is switched off once the chicks hatch, but the fence remains in situ until
the birds have moved away.
In areas where c. 50% of curlew nests were fenced, productivity was 0.41±0.21 chicks fledged/pair.
In areas where no nests were fenced, productivity was 0.16±0.03 chicks/pair (3 years’ data).
Fig. 28. Electrified netting around a curlew nest in Germany.
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Chapter 8. Key Electric Fence Components
Some definitions Volts The pressure behind the flow of electricity to push the energy along the conductive fence wire.
Most energisers produce up to 10,000 volts and about 3,000 volts (measured by a volt meter) is the
absolute minimum needed at the end of the fence to deter predators. However, the minimum
recommended voltage on a fence line to deter foxes is 4000-5000v.
Ohms The measure of resistance. Small diameter fence conductors, such as those in polywires and tape
have high resistance and are used for short fences. Large diameter wire such as 2.5mm high tensile
have low resistance and can be many kilometres long. Vegetation growth on a fence line acts like a
leak in a water pipe and "shorts" the fence to earth thus reducing its effectiveness.
Joules This is the amount of energy available to be pushed down the conductor by the energiser and
determines the distance of fence line that can be electrified satisfactorily. The higher the joules, the
longer the fence can be and the more consistent the shock produced.
Amperage The measurement of electric current and what is felt with an electric shock. The higher the
amperage the more intense shock the animal will feel.
Choosing and installing components with the appropriate specification An electric fence is a large open circuit waiting to be closed. The circuit is closed when an animal
standing on the ground touches the fence. The electric energy in the fence wire flows from the
fence, through the animal's body and to the ground causing the animal to be shocked. The animal
will only respect the shock if both the voltage and energy are at proper levels.
The two key components of an electric fence system are:
1. A battery or mains powered energiser produces a pulsed electric current along the fence wires.
2. An earthing rod(s) driven into the ground that returns the electrical pulse of energy to the
energiser.
The majority of electric fence problems arise from these two sources: the energiser is inadequate to
begin with and/or the underground rod(s) is incorrectly specified or installed.
Energisers Description The energiser converts low voltage (AC or DC) into repetitive high voltage pulses lasting 500μs
(microseconds) at one second intervals and delivers them along the entire length of the fence line.
Energisers can be mains or battery operated, although the latest dual-powered energisers offer the
best of both worlds and can either be plugged into the 240v main supply or connected to a 12-volt
rechargeable battery. Life expectancy of energisers should be at least five years (warranty periods
can be from 2 (Rappa) to 7 (Gallagher) years). The best models have a digital display of the fence
voltage and ground leakage (earthing).
77
Because the pulses of electricity are very short and the fence itself is not a complete circuit,
energisers consume very little energy regardless of power output. Typically a 1 joule energiser will
draw 4 Watts - a tenth of 40watt light bulb. However, energy consumption will increase the more
the fence is challenged e.g. the more vegetation that grows onto it, the more power it will consume.
Power supply Under most circumstances fence location will dictate the decision between a mains or battery
powered energiser. If remote from a mains supply the only option will be a battery powered unit. A
battery powered energiser will require either a battery charger and two batteries (one to be charged
and the other one ‘working’) or a solar panel that continuously charges the battery during daylight
(see below). A highered powered energiser may require a battery change as frequently as two
weeks or even less.
Where there is a choice, mains operated energisers are preferable: running costs are low (unlikely to
exceed £20pa), they are more more effective and the problems associated with changing batteries
are avoided. Whenever possible, a mains-powered energiser should always be sited inside a
building. However, mains operated energisers still need a separate earthing system (earth stakes)
(NB. It is illegal to earth the energiser to the mains supply or water pipes) and a special underground
cable to connect the energiser to the electric fence. It is possible to run High Voltage insulated
cable up to 500m from an energiser to the fence without significant power loss, but running a
cable over long distances can prove expensive.
Battery energisers should be installed close to the fence and off the ground to protect them from
insects and moisture. Usually energisers, batteries etc. are sited outside the fence to prevent them
being damaged by stock. However, an energiser positioned inside the fence will be better protected
from vandalism and theft. Suppliers sell vandal proof, ventilated, galvanised, lockable metal boxes
to house the energiser and battery.
Battery energisers clip directly onto the electric fence or earth post. To increase the period between
battery changes, a solar panel can provide a continuous trickle feed to maintain power levels and
extend battery life. The latest deep cycle lead-acid batteries coupled to a 45 watt solar panel can
prevent battery drain sufficiently for an energiser to power a temporary electric fence for a whole
season without the need for a battery change (see below).
Choosing the correct energiser The energiser must deliver a sufficient shock; without a strong shock predators will walk right
through the fence. Environmental, fence and ground conditions will all influence the level of shock
received. Therefore, the power output should be selected based on the following considerations:
location of the energiser (access to A/C power), type of animal to be excluded, length of the electric
fence, number of wire strands, the conductivity of the wire, whether vegetation is likely to touch the
fence and soil conditions for grounding. Higher powered energisers will burn off a fair amount of
casual vegetation and assist in maintaining a good fence, but should not be a substitute for proper
vegetation control (see here).
Output power The power of an electric fence energiser is measured in Joules (given as either stored or output).
Stored Joules relates to the energy (power) stored inside the energizer. Output Joules relates to
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how much energy (power) can travel from the energizer onto the fence line, powering the electric
fence; output joules are about 70% of the stored joules. Usually, the output joules of an energiser is
the selling point.
In an electric fence system, a high voltage is important for making sure that an electrical charge can
find its way through the fur of the animals it is intended to contain or exclude. The more or thicker
the fur, the greater the voltage required. The higher the voltage, the greater the charged wire’s
ability is to shock the animal that happens to touch the wire.
A 12 (stored) joule energiser has an open-line output of 9000volts/zero joules, at 500 ohms it is
approximately 3.6 joules at 6000volts but at 100 ohms it is 8.75 joules at 3000volts. This shows that
the longer the fence line and the more load (lower resistance) on the fence the more work the
energiser has to do to maintain a high voltage on the fence by transferring the stored energy to it.
There becomes a point where the maximum amount of energy is being transferred to the fence, but
the resulting voltage is too low to repel the animal (the voltage needs to be maintained in the range
5000 - 10000 volts to exclude predators). Check the voltage at the furthest point from the energiser.
Some drop in voltage, say1500 to 2000v is normal. A more than 2000-volt drop could mean that
your charger is underpowered for the fence.
Various rules of thumb are quoted for the power of energiser needed to maintain a secure voltage
along the electric fence but these seldom agree with each other. These vary from a minimum of 1
joule of output per 1.6km of fence regardless of how many strands of wire to 1 Joule per 9km of wire
(each strand of a multi-wire fence to be added up separately). Kencove recommend at least a 6
joule unit with an open circuit voltage of 9500 volts.
Fence manufacturers usually specify how many km of fence their different energisers will power
effectively. However, energiser manufactures and dealers tend to overestimate the length of fence
an energiser will power securely. Therefore, it is difficult to recommend a particular power of
energiser other than to say it wise to choose a higher powered energiser than you think you will
need and some would say that you can never have too much power.
Table 8 gives rough guide to the specification of the energiser needed to power a particular length of
fence under different conditions. A minimum of 10 Joules is required to 'burn off' grass as it comes
into contact with the fence. (The ability to 'burn-off' grass is extremely important for keeping wires
free of vegetation to maintain full power along the entire length of fence.) The length of fence is the
total length of conducting wire used in the fence. An energiser capable of powering 4km length of
fence can be used on either a 2 km fence of two wires or 1km of fence of 4 line wires.
If the fence forms a complete enclosure, the energiser can be connected anywhere along the fence,
but for line fencing (i.e. fences with a break) the unit should be placed as close to the middle of the
fence system as possible in order to maintain maximum output at both ends of the fence. For safety
reasons, two energisers should never be attached to the same length of fence!
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Table 8. The approximate length of fence energised by battery and mains energisers of different
power.
Fence length (km)***
Power*
(Stored joules)
Power
source
Open volts Estimated
battery
life**
No
vegetation
Average
vegetation
High
vegetation
1.7 12v 75Ah 28 days 22 3.5 1.3
1.6 12v 75Ah 9500 35 days 22 3.5 1.3
2.0 12v 75Ah 9500 26 days 25 4 1.5
3.75 12v 75Ah 9500 12 days 35 7.5 4
5.4 12v 75Ah 9500 7 days 40 11 6
1.4 220/230v 10200 n/a 12 2.5 n/a
2.5 220/230v 11000 n/a 20 3.5 0.75
5.4 220/230v 10200 n/a 35 11 4
7.5 220/230v 9500 n/a 30 7 3
14 220/230v 9500 n/a 53 15 5
18.5 220/230v 9600 n/a 70 20 7
26 220/230v 10000 n/a 100 26 10 * The amount of energy stored in the storage capacitor of the energiser, which is then discharged through the pulse
transformer onto the fence line. **Battery life and recharge times assumes that only 75% of the fully charged capacity is used before recharging. Batteries
should never be run flat. ***Distance of fence line which can be energised is based on multi-wire fencing constructed with 2.5mm high tensile
galvanised wire. Use average vegetation figures when calculating the distance for polywires, which are less conductive than high tensile wire.
The most powerful energisers are mains powered. Energisers with an output in excess of 5 Joules are not recommended under UK Health and Safety Codes of Practice. However, almost all manufacturers sell energisers more powerful than this (Table 9).
Table 9. The most powerful mains energisers sold by some well-known suppliers
Distributor/Manufacturer Output (stored joules)
Gallagher 7J
Voss 7.6J
Hotline 12J
Rappa 15J
Rappa also sell Speedrite Energisers with up to 36 joules stored output, with the proviso that these
are for ‘professional use only’. These are powering fences on several RSPB reserves (Table 10). PEL
supply even more powerful energisers than this (see Rye Harbour case study below).
Table 10. Specification of energisers in use at some RSPB reserves
Reserve Power Energiser Stored
Joules
Length of fence
(number of live wires)
Length of
wire (km)
Rainham Mains Speedrite 20000R 34 4.2km (5) 21
Greylake Mains Speedrite 36000R 36 5km (5) 25
Minsmere Mains Speedrite Panther 9800 14 2.0km (3) 6
Otmoor Mains Speedrite 60001 6.0 2.8km (3) 8.4
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Greylake Battery Speedrite 6000i 6.0 5km (6) 21
Cattawade Battery Speedrite 6000 6.0 1.7km (4) 6.8
Private Battery Speedrite 3000 3.0 0.65km (4) 2.6
Minsmere Battery Hotline HLB500 Falcon 1.7 0.6km (4) 2.6
Malltraeth Battery Speedrite 3000 3.0 1.7km (2) 3.4
Malltraeth Battery Speedrite 1000 1.0 1.7km (1) 1.7 1This replaced a 3J energiser, which could not adequately power the length of fence required. Power supply for battery powered energisers Battery energisers are designed to provide the optimum performance, whilst also maintaining
battery life. In general battery powered energisers are less powerful than mains powered
energisers. However, a battery (110Ah) powered energiser (1.5J) is easily capable of running
galvanised steel strained-wire fences over 1km i.e. maintaining a high voltage level (>6kV) for
periods of up to one month. However, electrified netting has much greater electrical resistance than
strained-galvanised wire and requires a more powerful energiser (and more frequent battery
changes if battery powered), than an equivalent strained wire fence. A guide to the performance of
different battery powered fence energisers is given in Table 11 below.
Table 11. A guide to the performance of different battery powered fence energisers (steel strand fence).
Stored
Joules
Voltage
(500 Ohm)
12V
battery
Min.
days1
Max fence length2
(no veg. growth)
Max fence length
(slight veg. growth)
No. of earth
stakes
0.8J 3.5kV 85Ah 22 4 km 2 km 2 x 1m
1.45J 4.3kV 85Ah 15 10 km 3 km 3 x 1m
2.6J 5.8kV 85Ah 9 18 km 6 km 4 x 1m
7J 6.8kV 105Ah 4 25 km 15km3 5 x 1m 1 The 12V battery needs to be recharged after the number of days indicated - this is necessary to prevent battery damage
through deep discharging. 2 Steel strand. 3 Reduced to 6m with heavy vegetation growth.
The number of days of battery life given as the minimum in Table 11 can be extended by selecting
the lower power settings available on some energisers. Some have a night-time setting which
reduces power output in the daytime. Switching from high to low power extends battery life
between charges by c.75%. Energisers also have built in power conservation features that prevent
permanent damage to the battery: when the battery voltage drops to 11.5 volts, the unit slows to
half speed to conserve power; when the battery needs recharging the pulse interval is extended to
conserve battery energy.
Choosing the correct battery Most energisers run-off conventional ‘wet’ lead acid batteries. Generally, these energisers are more
powerful than dry battery versions and can operate longer fences. The required voltage is specified
by the energiser manufacturer. The capacity of the battery can be determined from the proposed
usage and method of charging. The higher the Ampere hour (A/h) rating, the longer the period
between recharges.
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Batteries that are not designed for cyclic discharge and recharge (e.g. car starter batteries) will
deteriorate rapidly if not maintained at or near full charge. To run an electric fence, the battery
must be designed for cyclic discharge and re-charge. These are marketed as ‘leisure’ batteries or
'marine' batteries. They are intermediate between a ‘starting’ battery and a proper deep cycle
battery (see below). When not in use they should be trickle-charged occasionally to prevent deep
discharge, otherwise they will have to be replaced every year.
All RSPB reserves with battery powered predator exclusion fences use conventional lead acid
‘leisure’ batteries. However, the latest technologies are capable of powering a temporary steel
strand electric fence all season without a battery change (see below).
Solar panels Solar panels capture the sun's energy and convert it into electrical current. They can be used to
continuously charge a battery during daylight to maintain power levels and extend battery life with
energisers powered by a 12v battery. Solar panels should be positioned in open areas and close to
the battery, face south and be angled towards the sun (90⁰ to the incident light is optimum).
Solar panels are very reliable, especially if used with an appropriate regulator (‘charge controller’) to
protect the battery from being overcharged and to prevent reverse current drain. Expert advice
should be obtained before selecting a regulator to ensure that it is compatible with both the solar
panel and battery and does not consume more power than the panel produces! The latest solar
panels employ crystalline silicon technology to provide 'all weather' charging, even in the low light
conditions found in the UK. They are robust and water resistant and are appropriate for all kinds of
battery-powered electric fencing. Most come with a 20 year cell performance warranty
guaranteeing that the cell degradation rate will be no greater than 20% in 20 years.
Deep-cycle batteries Traditional lead acid batteries dominate more modern battery technologies mainly due to their
lower cost, predictable performance and high reliability.
Deep cycle lead-acid batteries were designed to store power for off-grid solar and wind power
systems. Deep cycle batteries have far heavier and stronger lead plates inside than ‘Leisure'
batteries, which makes them more expensive but better able to withstand a deep discharge.
Batteries designed for ‘leisure’ applications are now available. Sealed Gel (electrolyte in a gel-type
substance) batteries can complete around 400 to 500 discharge cycles (to 80% depth of discharge),
are maintenance free and do not leak acid, which makes them easier to install and transport than
conventional lead-acid batteries.
A further development is 'Solar' batteries. These are deep cycle 12v batteries with a very high
charge and discharge efficiency (90 to 95%), which are optimised to be able to be charged with very
little current to take maximum advantage of any available energy (see http://www.solar-
wind.co.uk/deep-cycle-dryfit-batteries-battery-uk.html).
A 200Ah 12v deep cycle gel battery (c.£350) charged by a 45w solar panel with a Speedrite 3000
energiser (supplied by Rappa for £265 and £205 respectively) could power a temporary steel strand
electric fence all season without a battery change.
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Connecting the energiser to the fence The cable that carries the electric pulse from the energiser to the fence needs to be specifically for
electric fences, with insulation rated for up to 20,000 volts (most fence chargers emit from 5000 to
10,000 volts)--the same degree of insulation as on automobile spark plugs. By using cable designed
for electric fences, you avoid the electricity leakage that results when you connect the charger to the
fence with standard household electric cable, whose insulation is rated for only 600 volts.
When attaching the cable to the fence itself, it is important to use a connector clamp rather than
just wrapping the cable wire around the fence; cable connected by wrapping comes loose more
easily or loses power due to oxidation or corrosion build up. All fence manufacturers sell connector
clamps designed to work optimally with their product.
Case studies
Rainham The reserve has two combination fences 3.7 and 4.1km long both with 5 live wires and powered by
the same model of mains energiser (Speedrite SPE 20000R supplied by Rappa). The energiser copes
comfortably with this length of fence even when there is some degree of vegetation contact. The
energisers are housed within buildings 12m and 30m from the fence respectively and connected to it
by an insulated wire running through lengths of buried plastic pipe. (RSPB has an account with Rappa
who provide good deals and after sales service.)
Cattawade The 1.7km combination fence has four live wires and is powered by a Speedrite 6000 (6J stored
Joules) energiser linked to a 110 Amp hour leisure battery. The battery is charged by a 45 watt solar
panel (c.4’ square) fixed on the roof of a conveniently sited barn. The energiser was chosen for its
array of functions; the intelligent version of the Speedrite 6000 (SPE 6000i) displays both output and
earth voltage and battery condition and can be switched on or off from anywhere along the fence
line, which makes fault finding easier. The reserve has two identical batteries, which are still in use
after 5 years. The spare battery is charged ready to swap if needed. This can happen in the winter
when light levels are low, but never in summer.
Greylake The 5km combination fence with 5 live wires is powered by a Speedrite 3600r mains powered 36
Joule stored output energiser supplied by Rappa. This model was chosen because it is mains
powered and suitable for long fences (5 strands x 5km gives 25km of fence line). The unit itself is
housed about 270m away from the fence and connected by an underground cable. The lead out
cable connects to one corner of the fence and the current then goes in both directions with the
“break” in the current being at the furthest point away. This gives the ability to find faults by section
of the fence (i.e. north/south) rather than having to walk the whole length of the fence to find them.
The combination fence replaced a strand fence with 6 live strands. This was powered by a battery
powered 6.0J stored output energiser (Speedrite SPE 6000i) with earth monitoring and the ability to
be switched on or off remotely from anywhere along the fence line. The fence worked well for a few
years with one or two problem years resulting from incursion by predators after power problems.
Then for 2 years running badgers learnt to get in by just going through the wires so it was replaced
with a combination fence and a more powerful energiser.
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North Kent All the reserves in North Kent have 12V 85Ah batteries charged by solar and wind in combination,
obviating the need to change batteries in order to recharge them. The fences have four live wires
and require two batteries each powering two wires via a Gallagher B280 (2.8J stored joules)
energiser. The fences run at around 6500 volts.
Rye Harbour Barry Yates has been operating electrified wire strand fences at Rye Harbour since 1980 and has
great experience of different powered energisers.
In the past he used a 10.4J mains powered energiser (Phoenix HMX 1500) for the main perimeter
fence (6.9km with three live strands) but this allowed badgers under it. For the other fences, he
used battery powered units of 1.7J and 3.8J stored power (Rutland ESB202 and ESB325 respectively).
From 2015 he has operated a 54J mains powered energiser (PEL 836) which powers c.9km of fence
(4 live strands) and a 18.3J battery powered energiser (PEL 415i) running a 1.6km fence off three
110ah batteries charged by one large solar panel.
The energiser units Barry considered were:
Power supply Make and model Stored power (joules) Price
Battery Gallagher B700 7J £530
Battery Rutland ESB375 5.4J £350
Battery PEL 415i 18.3J £450
Mains Rutland ESM 5500i 26J £750
Mains PEL 836 54J £830
Minsmere At Minsmere strand temporary electric fencing is used to protect stone curlew nesting plots 0.5- 1ha
in size). Electrified netting is used to protect nests of stone curlews that have laid outside of the
plots (4 or 6 x 50m lengths). The fences are powered by a range of different energisers producing
voltage readings on the fence of between 3kV and 6/7kV. These include Hotline (Falcon) energisers
that run off a battery but have solar panels that keep batteries topped up so that they rarely need
changing. The other energisers are powered by 12v 110mAh deep cycle (leisure) batteries (see
below). How long a battery lasts between charges varies (netting for shorter periods than wire
strands) but they are changed weekly regardless. Even so fence voltages are tested frequently, if not
daily.
Malltraeth (Tai Hirion) The Tai Hirion combination fence has a 1700m perimeter with three electrified strands: the top two
are run together and the lower one (knee-high) is run separately so that it can be switched off if
shorted out by vegetation. The two top strands are run by a Speedrite 3000 Energiser, and the
lower one by a Speedrite 1000 Energiser, both are set at the night-time setting, which reduces
power output in the daytime. The energisers are powered by 12v/110Ah deep-cycle leisure
batteries (Numax XV31MF, £77), which are trickle-charged by two 18watt solar panels (STP018, £74).
Batteries seldom need to be changed when in operation.
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This arrangement has worked well for five years. The solar panels, batteries and energisers are put
out in late Feb and taken in after the breeding season. The wires stay in place all year. The main
difficulty is maintaining the batteries when not in use. At first batteries had to be replaced every
year. To avoid this they must be kept cool and dry (above freezing and kept off the ground). They
are checked weekly and the most run-down are trickle charged to keep them topped up. By doing
this, batteries have lasted for several seasons’ operation. The fence could be kept operational all
year with the solar panels trickle-charging the batteries, but this was decided against because of the
weathering to the other components.
Earthing (ground) system)
An effective earth system is the most important component of an electric fence; ineffective earth
systems account for 95 percent of problems with electric-fencing. For an electric fence to give a
shock the current produced by the energiser must complete a full circuit. The current leaves the
energiser and moves along the fence wires through the animal, into the soil and back to the
energiser via the earth system. If the earth system is ineffective, the animal will receive an
inadequate shock.
The earth system comprises a series of galvanized-steel rods driven into the ground and connected by
an insulated cable to the "ground" terminal on the fence energiser. The current leaves the energizer
and moves along the fence wires. When an animal touches the fence, it feels a shock only when the
brief pulse of electric current goes through its body, into the soil and back to the energizer via the
earth system, so completing the circuit. This is termed a Ground Earth Return System (Fig. 29),
which works well in moist soils. .
Fig. 29. Ground Earth Return System.
However, dry peat, light or sandy soils and shingle are poor conductors of electricity and provide a
less effective earthing system. With this type of substrate there are three options 1) use additional
earth rods or 2) choose a better location for the earth system (such as damp soil) or 3) consider an
alternative method of earthing such as Fence Wire Earth Return (Fig. 30). An earth wire/ground
return system requires a fence with alternating electric and earth wires that are closely spaced
relative to an animal’s body size. This ensures that an animal trying to push through the fence makes
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firm contact with an electric wire and an earth wire and so is adequately earthed. Surface-laid wire
netting aprons are advantageous in this respect – they not only prevent animals pushing beneath a
fence but also effectively earth any animal standing on them.
Fig. 30. Fence Wire Earth Return System
The earth wires are joined with joint clamps (just like the live wires) and connected to the ground or earth terminal of the energiser Fig. 31a). When attaching the cable to the fence itself it is important to use a proper connector clamp rather than just wrapping the cable wire around the fence. The earth wires should also be earthed adequately (no voltage on them) every kilometre (Fig. 31b).
Fig. 31. (a) Connection arrangements between earth and live wires, the energiser and the earthing/grounding system. (b) Earth wires can be connected to ground rods at regular intervals.
The number of earthing posts or stakes (ground rods) The earth system comprises a series of galvanized-steel rods or pipes driven into the ground and
connected by an insulated cable to the ‘ground’ terminal on the fence energiser. The number of
galvanised earth stakes required depends on the type of energizer used to power the fence and the
soil conductivity. Energisers generally require a minimum of one x 2 metre earth rod driven into
(a) (b)
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damp soil to be efficient. Larger fence energisers exerting more power, or longer fence lines with
higher leakage, require substantially more earthing. As a rule there should be 1 metre of earth rod
for every joule of energy i.e. a 6 joule energiser will require 6 metres of ground rod (earthing stake).
Typically this would be three 2m ground rods, spaced at least 2-3 metres apart and connected with
an insulated lead out cable. The drier the soil, the more extensive the earth system needs to be, so
additional earth stakes will be required. It is probably wise to consult the energiser supplier about
the correct number of earth rods for your specific application and location.
Long earth stakes driven deep into the soil give far better earthing than the same total length at
shallower depths, because soils are moister and have more conductive minerals at lower levels.
Therefore, two 3m rods driven deeply into the soil would be better than three 2m rods. Large
diameter pipes have a greater soil contact surface, so are better than thin rods. The more soil/metal
contact that can be achieved the better.
Usually, earth rods or pipes can be driven into the ground with a conventional post hole driver
(sometimes used upside down). However, earth rod driving hammers are available that can
significantly reduce installation times or enable installation where ground conditions are
unfavourable. It is difficult to earth energisers powering fences on shingle. Even narrow 1m earth
rods are hard to drive into the ground, so in this situation it is easier to have twice the number of 1m
rods than to use 2m rods (Barry Yates pers comm.).
All parts of the earth system should be made of the same metal. Earth stakes should be hammered
into the ground, except for the last 10cm so that they can be linked together with insulated heavy
duty galvanized lead-out cable, which is then connected to the energiser's earth or ground terminal
i.e. there should be one continuous cable through the earth system. The cable should contain 2.5-
mm (16-gauge) galvanised wire - not thinner and not copper wire, which causes electrolysis at the
joins. It must be insulated because it lies on the ground surface throughout year and must not rust
(rust is a poor conductor). The insulation should be stripped off where it is clamped to earth rod. It
should be clamped as tight as possible with a bespoke connector clamp to give the best positive
contact between cable, clamp and rod. (For a good instructional video on earthing see
https://www.pel.co.nz/en/instructional-video/earthing.)
Where to site the earth system The earth system must be at least 10m away from any other earth systems e.g. house mains,
underground power or phone lines, away from stock or other traffic that could interfere with the
installation and be easily accessible for maintenance. However, the most important factor is that
the soil in the area chosen for the earthing system should be moist all year round (e.g. choose a
shaded or swampy area). If the moisture level in the soil is too low (i.e. during a dry year or in
extremely sandy soil), the ground rods will begin to lose their ability to pull electrons from the soil.
Improving earthing in dry soils If there is no wet area within a few hundred metres of the energiser which could be used, a system
of keeping the area around the earth rods pipes moist should be devised. If necessary, the area
around the ground rods should be watered during dry weather. Alternatively, a galvanised wire
should be run along the bottom of a fence to a moist area, and then more earth stakes installed at
this point.
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In very dry sandy soils, consider investing in a bentonite earthing system. Drill large holes (3 inches
(75mm) in diameter or larger) in the soil, set the rods or pipes in the centre and pour the bentonite
slurry mix into the hole around them. If kept moist, this system can improve earthing by up to ten
times. An alternative is to pack the holes with ordinary clay and embed the ground rods in it.
Testing the earth system The earth system should be checked with a voltmeter (see here) immediately following installation
and then at periodic intervals to insure adequate grounding of the electric fence. This should be at
least once during the driest period and once during the wet season each year.
The more voltage flowing to the earth, the less power the fence will have. It is best to have no
voltage on the earth system, but a maximum of 200-300 volts are acceptable when the fence has
been shorted out to as low a voltage as possible. If excessive voltage readings are found, more earth
stakes should be added at 3 metre spacings until the voltage falls within tolerance levels. Remember
that an earth system installed in winter, which is adequate for winter conditions, may not be suitable
for summer. This may explain any substantial loss in power in the electric fencing over the summer
months. During dry seasons or during seasons when there is excessive growth of vegetation on the
fence line, it may be necessary to upgrade the earth system by adding more ground rods.
How to test the earth To test an earth system, the fence must first be shorted out. Testing an earth system without the
fencing shorted out is a waste of time. Shorting out the fence creates the maximum current flow so
puts a load on the earth system. If the earth rods or pipes can't handle the flow there will be a
voltage reading at the energiser terminals. If there is no voltage, then the earthing system is
satisfactory.
To test the earth system:
1. Turn off the energizer.
2. Short circuit the fence
Short circuit the fence to ground at least 100 m away from the energizer by leaning 3 or 4 steel rods
or pipes or an iron bar against the hot wire(s) of the fence. In dry or sandy soils, the rods should be
driven 30cm into the soil. Another method is to push several pieces of fence wire into the earth and
wrap the opposite ends around the hot wire.
3. Turn the energizer back on
4. Measure the fence voltage with a digital voltmeter
Check the fence line voltage with a digital voltmeter. As a result of shorting the fence, the voltage
should have dropped below 2000V. If more than 2000v, continue to short the fence by leaning
more steel rods or pipes or by making wire connections to ground at >100m from the energiser until
the fence line voltage drops below 2000V. (NB. With some high-powered fence energizers you may
not be able to short the fence below 2000V. However, you can still test the earthing at this higher
voltage.)
5. Test the energiser ground system.
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Connect one lead of the digital volt meter to the top of the earth rod of the earthing system that is
furthest from the energiser. Push the probe at the end of the other lead as far as possible into damp
ground and as far away as possible (>1m) from the earth rod i.e. at the full length of the lead.
Alternatively, connect the lead of the digital voltmeter to a 12-inch metal stake driven into the
ground >1m away from the last fence energiser ground rod.
7. Check the voltage reading
The voltmeter reading should be no more than 200-300V and ideally zero. If the voltmeter reading
is below 200V, the ground system is adequate and the electric fence energizer will provide near
maximum performance. If the reading is higher than 200v, the earth system is inadequate and you
should install extra earth rods connected with lead out cable at three metre spacings until the
voltage falls back down to near zero. Alternatively, move the ground system to moist soil until the
ground system voltage is below 200V.
8. Remove the short from the fence.
Some common grounding issues 1. There is a bad wire connection to the ground wire. Check to make sure the wire is securely
fastened and is not frayed.
2. Additional grounding rods are required due to dry soil conditions.
3. The wrong type of earthing rod/stake was used. It needs to be galvanized steel rod or pipe at least 1-2m long.
4. The earthing rods were not long enough. In the case of dry soil, it may require 2-3m of galvanized steel to reach a moist area of soil below ground.
5. The ground conditions change due to extreme drought or heavy vegetation and so additional rods need to be added.
Cut-off switches Cut-off switches may be incorporated anywhere in the fence where the power needs to be
disrupted. Multiple cut-off switches allow sections of the fence to be isolated for easier trouble-
shooting and enable portions of the fence to be isolate to facilitate alterations/repairs without
closing down the whole fence. It is also a good idea to install cut-off switches on both sides of a
gate.
Insulators Insulators are used to attach wires to the fence posts while at the same time preventing them from
contacting any surface that could cause current to leak. The type of insulator needed is determined
by the choice of electric fence. Most fence suppliers market insulators specifically suited to their
fence products.
Be careful when deciding which insulators to buy. Sunlight deteriorates plastic, so it is important to
only buy good-quality, long-lasting insulators (usually black ones) that are treated to resist
degradation by ultraviolet light. Poor quality insulators tend to turn white or clear after a few years
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in direct sunlight. Cheap ‘generic’ insulators are usually made of brittle plastic, which only lasts a
few years before breaking.
Insulated Cable Heavily insulated lead out cable that is custom-made for electric fencing is the only safe option for
connecting mains energisers to electric fence lines and earth stakes, and for carrying the power
across gateways.
Posts Posts provide the backbone of an anti-predator fence, supporting the fence wire and keeping it
evenly spaced and tensioned. As such, posts should have a lifespan and specification that matches
that of the other components of the system. To achieve this it is important that posts are of the
appropriate quality and yet this important aspect is often neglected.
By their very nature, many reserves provide a challenging environment for wooden fence posts.
Often they are subjected to alternating very wet and very dry conditions, and posts which are
satisfactory in stable situations cannot cope if subjected to frequently changing conditions. The
lesson is not to buy wooden posts entirely on price, and especially do not buy the cheapest fencing
posts you can, otherwise the result could be a maintenance nightmare.
Choice of material Supports for temporary fences may be wood, metal, plastic, or fibreglass. However, more
substantial and durable materials such as metal stakes or timber posts are required for (semi-)
permanent fencing. In the UK, the usual practice is to use treated softwood posts rather than
galvanised steel posts to support fences. Wooden posts usually look ‘nicer’ and if steel posts are
used anywhere in an electric fence, then reliance is entirely on the insulators to keep the fence from
shorting out. No matter how good the insulators, one will break eventually creating the potential for
dead-shorting. Also, galvanised steel posts are considerably more expensive than their wood
equivalents.
However, wooden posts can present their own problems for exclusion fences. Wood provides an
excellent climbing surface for foxes (and cats) and this increases the chance of the fence being
breached.
Desired service life Always buy rot-resistant posts, such as a treated post or a post made of wood that is naturally rot-
resistant. Wet conditions increase the risk of fungal decay and untreated wood posts will rot and fall
over in as little as 6 to 8 years, while substandard wooden posts can soon split allowing some of the
insulators to fall out and the fence to short.. Different uses for wood require different treatment
cycles and not all posts sold as ‘treated’ will perform equally. Timbers that are suitable for in-ground
use like fence posts will need to be preservative treated in accordance with BS 8417: 2011 for British
Standard use class four, which should give a useful service life of about 15 years (a 15 year desired
service life is the default option for fence posts). However, if you want posts to last 30 years, opt for
the gold standard, which is use class five. Not all tree species though are suitable for a service life of
30 years and specifying a 30 year desired service life will incur significant additional cost. The price
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differential is inevitable because of the species, process cycle and additional preservative required to
achieve such a specification.
In order to ensure timber fence posts that are long lasting, buyers must specify their requirements
clearly, preferably in writing, and ensure they receive clear documentation at the point of delivery to
confirm that their requirements have been fully met (e.g. use class 4 compliant). Preferably, the
posts themselves should be marked individually with resilient labels or branding.
Choice of wood The most common species grown in the UK are spruce, which is a white wood, and pine, Douglas Fir
and larch, which are all redwoods. For fence posts it is better to use redwoods. Tanalised (see
below) sweet chestnut posts are a hardwood alternative, but are more expensive than softwood
posts.
Pine (redwood) sapwood is classified as permeable in British Standards and is most amenable to
treatment because its natural permeability means the penetration and retention of preservative
required for a use class 4 specification can be achieved more easily. It is suitable for both 15 and 30
year specifications. Spruce (whitewood) sapwood is classified as being resistant to preservative
impregnation. Therefore, while spruce is permitted in BS 8417 for use class 4 applications, particular
expertise is required to achieve the necessary penetration and retention of preservative. Seasoning
to the correct moisture content is vital and special techniques, such as incising the wood before
treatment or longer oscillating pressure cycles, will be necessary to achieve the required
penetration. The Wood Protection Association’s new Benchmark Scheme verifies that incised UK
spruce fence posts comply with a 15 year desired service life standard.
Although the sapwood of other species such as Douglas fir or larch is classed as resistant to
treatment like spruce, experience shows that achieving the required BS 8417 penetration and
retention in such species is more reliable than for spruce.
Treatment Newly felled timber has a very high moisture content, often up to 150%, with all of the cell cavities
within the wood full of liquid. The process of removing this liquid so that the wood is suitable for
construction is called ‘seasoning’. Until the majority of the liquid is removed and the cell cavities
emptied, there is little or no chance of achieving the penetration necessary for successful
preservative treatment. For this reason one of the main preservative treatment parameters
recommended by the manufacturers is to ensure that wood is around 28% moisture content at the
point the treatment process is applied, although this varies according to species. (WPA recommends
28% or below for pine and between 28% and 40% for spruce.) Timber which is not sufficiently dry
will not absorb the preservative properly. Although some manufacturers kiln dry timber posts, air
drying, if done correctly, is better as the wood is less likely to become brittle.
How is wood treated? The timber is put into a pressurised chamber, which forces the preservative deep into the wood
structure. The resulting timbers have a distinctive pale green colouration when freshly treated.
Although “tanalised” has become a generic term for green treated timber, it is only wood treated
with TANALITH™ E wood preservative, a combination of copper and organic biocide ingredients, that
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that can be branded as ‘Tanalised’, as other treatments may not deliver the same protection. The
preservative treatment to BS 8417:2011 should be either Tanalith TE/gFb or equivalent.
The preservative should penetrate evenly to at least 6mm depth. Suppliers should be happy to
demonstrate the level of preservative penetration by cutting across a sample fence post. However,
it is not just the choice of preservative that is important. Timber species, moisture content, the
treatment process, and final handling at installation all have a critical role to play.
Be aware that many of the chemicals used to treat conventional fence posts are not allowed by
some organic certification regulations. If this relevant, always check with the organic certifying body
before installing the fence. When in doubt, request the Material Safety Data Sheet for the fence
post treatment chemical from the fence post supplier so you can get your organic certifying body to
sign off your fence posts (in writing) before starting installation of the anti-predator fence.
Additional treatment to prolong fence post life In recent years, changes to the legislation have meant that harmful but effective chemicals have
been removed from fence preservatives making effective treatment more difficult. Furthermore,
because the preservative is embedded deep in the timber cells, it remains there for the lifetime of
the fence and so there is very little benefit trying to add subsequent brush-on products to extend
the service life of the timber. However, additional treatments to prolong fence life have been
developed based on the premise that dry timber tends not to rot. (Research by the Timber Research
& Development Association (TRADA) has established that timber kept below 20% moisture content
is less susceptible to fungal decay.)
Tuffdip Tuffdip is a bituminous solution which seals out moisture and seals in any prior chemical treatment.
The bitumen base is inert and non-toxic and so is suitable for use around watercourses and near
sensitive plants. Tuffdip is water-soluble when wet but dries to a tough, non-porous skin that is
bonded to the timber. It can be applied cold to the required underground depth plus 100mm (4")
with a brush or by dipping the posts for a maximum of ten minutes. Drying time varies from 2 hours
in ideal conditions up to 48 hours in cold weather with high humidity.
Once cured, Tuffdip seals the whole of the treated area of the fence post against water ingress and
forms a physical barrier inhibiting the development of rot and fungal infestation. Posts treated with
Tuffdip had a moisture content of below 20% even when immersed in water for more than a month.
Conventionally treated posts subjected to the same conditions showed a moisture content of >40%.
Tuffdipped posts can be driven into stony ground without damaging their moisture resistance.
25 litres (£156) Tuffdip is enough to treat c.400 posts. At this application rate, the cost per post is
40p but it should double the lifespan of the post.
‘Postsaver’ post sleeves Wooden fence posts tend to rot through and break within 200mm of ground level (the ground line).
Postsaver sleeves comprise a tough polythene outer layer with a meltable bituminous liner. Heating
with a pallet shrink gun or a gas blow torch shrinks the sleeve onto the fence post at the vulnerable
ground line section. Use of Postsaver barrier sleeves is claimed to double the life of fence posts by
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sealing in preservatives and keeping decay out, giving a typical expected service life well in excess of
15 years.
Postsaver sleeves can be fitted to most sizes of post from 75mm x 75mm square or 75mm rounds up
to 200mm square or 150mm rounds. Sleeves vary in price from £1.62 for 75mm to 100mm Rounds
up to £4.67 for 150mm x 200mm square or 150mm round posts.
Aftercare Ideally once preservative treatment has been carried out, no re-working (e.g. cross cutting, notching,
boring or pointing) should be carried out. Where such work is necessary, it should never be below
ground and all newly exposed surfaces should be brush treated in accordance with the preservative
manufacturer’s recommendations e.g. with an end-grain preservative such as Ensele (a water based
brush-on copper/triazole preservative) to maintain the integrity of the protective system. Without
this treatment, water and insects can easily attack the timber at the untreated site.
Always place an uncut end in the ground. Cross cut ends of posts should always remain above
ground and be cut at an angle, or finished with a post cap. In both cases all exposed surfaces need to
be brush treated in accordance with preservative manufacturer’s recommendations. If posts need
to be shortened, the cut end should always remain on top, and not be used in contact with the
ground.
Where possible ensure water can drain away from the foot of the post, especially when they are set
in concrete. Failure to do so will mean the post stays wet for long periods increasing the risk of
decay.
Post dimensions The required length of posts will vary according to the height of the fence (see rough guide below)
and the depth to which they are sunk into the ground, which is dependent on soil texture and
whether the post is set in concrete. Posts can be square sawn or round timber. Post diameter
depends on the strength of the fence. A 5- or 6-strand high-tensile fence would need 150mm-
diameter posts.
Posts Struts Intermediate posts
Fence height (m) Length
(m)
Section
(mm)
Length
(m)1
Section
(mm)
Length
(m)
Section
(mm)
Square posts
1.5 1.85 125x125 1.60 75x75 1.7 75x75
1.6 2.0 125x125 1.75 1.8 75x75
Round posts
1.15 2.30 130 (diam.) 2.30 100-113
(diam.)
1.90 80-100
(diam.) 1 Length suitable for struts fixed at a 45 deg. angle on level ground
Construction Fencing should be constructed in straight lines and be strained between strainer posts. Strainer
posts should be used at each end of the fence and at least every 100m and also at all changes of
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direction and sudden changes of gradient (especially at the bottom of dips/hollows). Corners need
special consideration during fence planning and construction. The better supported netting at posts
and corners makes climbing easier for feral cats and foxes, as do ‘internal’ corners. Therefore,
wherever possible the latter should be avoided. To protect vulnerable places such as corners extra
netting should be added to provide an outward facing overhang.
High tensile wire requires firm straining posts at every change in direction of the fence line.
Corner/strainer posts must be set deeper than line posts to withstand the strain of supporting the
fence line. As a rule of thumb the depth in the ground of corner posts should be equal to, or greater
than, the height of the top wire and strainers placed in a hole at least 0.9m deep and properly
rammed, firmed (using stones where necessary) and strutted in the line of the fence. Two struts per
post should be used on changes of direction except on acute corners <90 degrees where a single
strut bisecting the angle of turn may be used. The point end of the strut should be housed in a notch
c 7.5-10cm deep cut in the straining post between halfway and two thirds up the post and facing the
direction of strain. The bottom end should be dug into the ground and rest tight on a half stake
driven into the ground or a large stone well bedded below ground level.
In soft ground or on shingle, box strainer assemblies should be used in place of conventional
strainers to achieve the required tension. These comprise 2 posts set approximately 2m apart with a
wood stake fixed between them at the top and a strained wire diagonally fixed at ground level at the
corner post (see Appendix 9).
Intermediate posts or stakes should be driven into the ground in line with the posts to a depth of at
least 0.6m. Spacing between posts is simply a matter of maintaining a reasonably consistent wire
height along the fence line. The maximum distance between stakes should normally be 6-10m for
2.5mm high tensile steel wire.
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Chapter 9. Reducing the challenge to predator exclusion fences
Fence design Most animals that encounter a fence will first attempt to push under or through it (Lund and De Silva
1994, Day and MacGibbon 2002). Therefore, the lower sections of the fence in particular must be
meticulously constructed and maintained.
The pressure on the fence will be greatest at corners with inside angles (i.e. angle on the outside is
<180⁰). Animals often walk along the fence-line until they reach a corner and then attempt to cross
it at this point (e.g. Day and MacGibbon 2002). The route of the fence should be chosen to minimise
the number of corners especially angles on the outside of less than 120⁰. Corners less than 120⁰
enable foxes to brace themselves against the fence making climbing easier. Also, avoid or minimise
external fence features, such as strainer post stays, which will aid animals that attempt to climb or
jump the fence.
Gates and ditch crossings are often weak points exploited by foxes and badgers (see below). The
number of gates and waterway crossings in a fence should be minimised and care is required to
ensure these features function effectively and yet still form an adequate barrier to predators.
Wire aprons to deter burrowing Foxes and badgers will attempt to burrow under the fence and will readily exploit holes created by
rabbits. Wire netting aprons placed horizontally on or beneath the ground at the base of the fence
will deter them from pushing or digging beneath the fence. They are effective at reducing the
frequency of burrowing under a fence, even if they do not always eliminate the problem. Note that
the apron must be on the outside of the fence!
Experience in Australia suggests that most attempts at burrowing over a shallowly-buried 40cm
apron occurred within 20cm of the fence base, with only 11% of diggings occurring 20-40cm from
the fence and 1.5% occurring further than 40cm away. Research in New Zealand using rabbits
resulted in similar findings (Day and MacGibbon 2002). For this reason the most frequently used
apron widths are 30-60 cm. Both studies concluded that horizontally buried aprons are more
effective than those that are buried vertically as animals that encounter the latter situation
sometimes continue to burrow down until they are able to pass under the apron. Aprons should be
reinforced with wider netting or heavy rubber matting in areas of soft erosive substrate such as
dunes and watercourses to prevent rabbit incursions (Moseby & Read 2006). McKillop et al. (1998)
also recommended increasing the horizontal foot apron by up to 1m in areas favoured by digging
rabbits.
Aprons laid on the surface can be secured to the ground by pegging it down, or simply by letting
grass grow through the netting. This is cheaper than digging trenches unless a netting plough
machine is used. However, if the apron is not secured properly, burrowing animals may learn to
push under sections of the netting where slight puckering occurs. Where soils are hard and difficult
to dig in, a well-secured, surface-laid apron is probably sufficient. However, where soils are soft and
burrowing animals likely to be problematic, an apron that is buried just below the surface is likely to
work best. However buried aprons typically corrode faster than surface-laid aprons because of the
moisture retention in the soil.
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When creating an apron a separate length of netting can be used and clipped to the vertical netting
near the ground. Alternatively a greater width of netting can be used so that it can be bent to make
the horizontal apron continuous with the vertical netting (see here). This approach is easier and less
labour intensive and decreases the chance of burrowing animals exploiting gaps that may develop
between the clips near the base of the fence where the two pieces of netting are joined. The
disadvantage is that when the apron netting corrodes (which will occur considerable faster than the
vertical section of netting that is not in contact with the ground), a much larger section of netting
will need to be replaced and this will be more expensive. When corrosion occurs, completely
removing and replacing the netting is preferable to attaching a new apron on top of the old layer,
because ‘sacrificial rusting’ will occur, causing the new netting to corrode considerably quicker than
it otherwise would. The method used to create an apron should therefore be determined based on
the likely frequency with which the apron will have to be replaced (which will vary according to the
environment the fence is to be constructed in) and the predicted material versus labour savings that
each of the methods would confer.
Gate design Access gates are often considered to be the weakest points in exclusion fences. Although gates
primarily function to allow human access to the fenced enclosure, they must also function as an
effective barrier to predators. Therefore, the design principles that apply to fences must also apply
to gates.
Gaps Gaps in, below, or between gates must be smaller than the maximum wire netting size used in the
fence if an adequate barrier is to be maintained, otherwise a fox will be quick to exploit it (Fig. 32).
Gates must be hung on posts that are NOT strainers; gate hanging and clapping posts must be
separate from the fence line. .
Gaps, such as wheel ruts, quickly form beneath gates unless measures are undertaken to prevent
this. These include installing a solid concrete or wooden plinth (e.g. sleepers) immediately beneath
the gate or the use of limestone to strengthen the ground below the gate in order to prevent holes
developing. At the Nene Washes, to stop animals burrowing beneath a gate, a channel was dug
under the main gateway and filled with type 1 (crushed concrete) to give a level foundation. Then
old railway sleepers were used as a base to lay a 180mm thick steel channel beam bolted to the
hanging and clapping post. The channel was then filled in with brick and capped with type 1.
A wide, single, vehicle gate is preferred to double opening vehicle gates as gaps can form between
the latter. When gates are secured with a chain and padlock, the chain should be shortened so that
the ends of the chain just meet, and the gate must be tightly fastened. However, a more secure
locking mechanism that ensures the gate is correctly aligned when closed is preferable to a simple
chain and padlock system.
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Fig. 32. A fox jumping through a 15cm gap between the gate and the barrier fence at Wallasea. Note
that the floppy top butts right up against the other end of the gate with no gap.
If the gate functions solely as a barrier, in addition to sealing any gaps, measures should be taken to
prevent an animal scaling the fence, such as the continuation of the curved floppy top of the fence
across the gateway (Fig. 33).
Fig. 33. Two gates within predator exclusion fences. The gate on the left is ‘protected’ with wire mesh with a shallow angled rigid overhang that would provide limited effectiveness against a determined climbing fox. The gate on the right is better. Note the lack of gaps between or around the gate and the continuation of the fence design across the gate (floppy top) to maintain an effective barrier.
Electrified gates The same principles that apply to the spacing of electric wires in the main fence body should be
applied to gates. The same configuration of electric wire strands should be continued across the
gate. These can be electrified tape, elasticated rope or, more commonly, steel wire springs attached
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to isolators allowing the strands to be removed to allow safe access through the gate when needed.
Electric wires must not be offset too far from the plane of the gate to so that any animal climbing it
will receive a shock. To transfer power from one side of a fixed gate to the other use a bespoke
underground gate cable i.e. do not rely on the contact between the gate hook and insulator to
supply power to the rest of the fence (Fig. X).
Fig. 34. Electrifying a gateway to prevent animals from climbing the gate.
Reducing predator ‘pressure’ The level of ‘pressure’ placed on a fence by predators is likely to be dictated by their density outside
the fence, and the relative abundance of resources (particularly food) inside and outside. The
effectiveness of fences is likely to be increased if there is less ‘pressure’ on the fence from predators
trying to penetrate it.
Lethal control One reason for installing anti-predator fences is to reduce the need for lethal fox control. However,
lethal fox control prior to bird breeding season will reduce the rate at which foxes try to penetrate
the fence. This may be particularly important in the first year of operation. Foxes whose home
range includes the fenced area are likely to persist in trying to penetrate the fence. If fox control is
instituted around the fence prior to bird breeding season in its first year of operation, the individuals
with local knowledge are likely to be removed.
In subsequent years, the level of fox activity around the fence should be monitored (with trail cams
etc.). If this shows heavy fox usage around the fence, consider re-introducing control. In addition,
lethal fox control will probably be necessary to remove any foxes that do manage to get inside the
fenced area.
Non-lethal methods Non-lethal ways to reduce pressure on the fence are largely untested in the UK but could include
providing an alternative food source nearby either by habitat manipulation (e.g. creation of rough
grassland to provide a small rodent food source) or diversionary feeding (e.g. of badgers or raptors).
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Flashing lights Several companies market flashing red lights which are claimed to deter foxes from approaching a
fenced area at night so making the fence more effective. Gallagher market ‘Fox Light’ which consists
of nine LED lights which flash randomly to give the impression that someone is patrolling in the area.
The video link below compare four popular flashing light, solar powered predator deterrent units:
https://www.youtube.com/watch?v=cZR6G6_dWMI
Reducing avian predation Unfortunately posts used for fencing provide vantage points for potential avian predators such as
crows and kestrels. A large number of inventive measures have been used to try to prevent this
such as plastic pigeon spikes or inverted cut plastic bottle tops nailed to the post tops. At Rye
Harbour, hammering a single 6” screw from Screwfix into the top of small diameter posts, and up to
5 or 6 screws on larger diameter posts, has prevented most ‘problem’ birds from perching on them
(B. Yates pers comm.).
Electric Fencing Training Aids
Often predators are inquisitive and investigate an electric fence without any encouragement and by
so doing experience an electric shock which leads to them avoid the fence subsequently. However,
some individual animals do not learn to ‘respect’ the fence and instead get used to traversing it.
These can be ‘trained’ to avoid the fence in future, thereby increasing its effectiveness by attaching
commercially available ‘Bait Caps’ or other unfamiliar objects or food items to the fence. Cotton
wool soaked with suitable bait and attached to the fence can be extremely effective at encouraging
animals to experience a shock, which causes them to refrain from trying to penetrate the fence in
future. This training is especially applicable to badgers and foxes. For foxes people have tried using
some dripping or meat or gravy residues e.g. from the Sunday roast or wrapping strips of bacon
around the wires at regular intervals around the fence, about the height of a fox’s nose. For badgers
try honey, syrup, peanut butter or treacle. Usually, a positive effect is seen immediately and baiting
is not normally required a second time. Note that if an animal is already respecting the fence there
is no need to bait it; this is only for those animals which are proving to be difficult.
When should predator fences be operational? All animals dislike the feeling of an electric shock. After one or two encounters with an electrified
fence, most animals will quickly learn to avoid the area enclosed by the fence. NEVER turn the
electric fence off when animals are in the vicinity as when they touch the fence without receiving a
shock, it can cause the psychological imprint to be diluted. Similarly, animals may continue to cross
an electrified fence that was not electrified when first encountered. For this reason strand electric
fences should go live as soon as they are installed so that animals do not get used to traversing them
before the fence is electrified. Any length of electric fencing constructed should be made live
(including the earthing arrangement) the same day to ensure any animal touching the fence always
receives a shock. A further section can be completed and electrified each day. Both the fence and
power source should be removed immediately the need for a fence stops.
Similarly, it is best to keep the electric strands of combination fences live throughout the year rather
than just during the breeding season. Most anti-predator fences at RSPB reserves are operational
throughout the year (Fig. 35). However, at Otmoor, one gate is opened in August to allow cattle to
have free movement to graze the grass strip around the fence. When the cattle leave the site in
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October/November, the other two gates are opened to allow hares (and predators) to move in and
out. In January, two gates are closed, but one is kept open. A trail camera records fox movements
through the gateway. Foxes passing through regularly are shot. The gate is closed some time in
February.
Fig. 35. Operation of anti-predator fences on RSPB reserves. NB. Does not include barrier fences (permanently operational) or temporary stone curlew fences.
28
7
2All year
Breeding season only
Fence removed outside breeding season
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Chapter 10. Fence monitoring and maintenance If they are to remain effective, anti-predator fences need to be monitored regularly and any faults
rectified immediately to ensure they are functioning to their full capacity.
Regular visits should be undertaken all year round to ensure that: 1) vegetation is not touching the
fence, 2) the voltage of an electrified fence is at the required level, 3) the structure is maintained to
the required specification and 4) no target predators are present in the enclosed area.
No fence is totally effective against foxes and site managers must be vigilant to detect those that
enter fenced areas and then to eliminate them quickly. The surplus killing behaviour of foxes means
that a single incursion into a fenced enclosure may spell the demise of a considerable number of
nests of the target species. To prevent delays in finding foxes within the enclosed area and
removing them, it is recommended that a response plan is formulated. This should include obtaining
prior permission to shoot any foxes discovered inside the fence from the RSPB Reserves Standards
Group at The Lodge.
Monitoring
Frequency As a general guideline, most operational fences should be monitored at least weekly. More frequent
monitoring in the period immediately after construction may be warranted to detect construction
flaws, to detect the presence of foxes or badgers within the fence and to check for effects on non-
target species, which might have a higher rate of collision/entanglement until they become
accustomed to the presence of the fence.
During the breeding season, the power supply of electrified fences should be checked daily (see
below) and there should be at least weekly inspections to check whether vegetation is about to
touch live wires. Barrier portions of fences should also be checked weekly for any damage, e.g.
‘unofficial’ holes in the fence or dug underneath it. At the same time, systematic monitoring should
be in place to detect the presence of large mammalian predators within the fence (see later). This
applies equally to all types of fence.
In a study of predator exclusion fencing for areas of high conservation value in Australia (Long and
Robley 2004), the frequency of checks depended on the length of fencing to check. Even so 80% of
fences were checked at weekly intervals or less (Table 12).
Table 12. Frequency of fence checking for predator exclusion fencing of areas of high conservation value in Australia (Long and Robley 2004)
Frequency Number (%)
Daily 1 (5)
2–4 times weekly 6 (30)
Weekly 9 (45)
Fortnightly 2 (10)
Monthly 2 (10)
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Monitoring voltage Monitoring should ensure the fence remains live and is not allowed to be without power for any
period. While learned avoidance of electric fences means that individuals of some species are likely
to respect the fence during short-term power failures, voltage should be checked daily in the
breeding season so that electrical shorts or other malfunctions can be detected and fixed promptly.
Alternatively, automated monitoring systems are available that can provide an immediate alert of a
drop in voltage. The Fence Watch Electric Fence Monitor from Rutland Electric Fencing is a 24 Hour
Solar Powered Electric Fence Monitor and SMS Notification System. It operates alongside any make
or type of energiser and can be used with any SIM card and mobile phone. The status fence of the
fence can be checked from a mobile at any time. Customisable features include an automated daily
status report and low fence voltage text alerts. It costs c. £200.
To impart a shock of sufficient strength, the voltage should be maintained as high as possible with a
minimum of 5 kV under dry conditions and 2 kV in wet conditions. To perform satisfactorily, most
fences need to operate at c.6-7000v.
Voltage checking A proprietary fence tester will read exactly how many volts are on the fence at any point and should
be used to check whether the fence is providing sufficient voltage. Reliance on grass stems or twigs
provides only a crude indicator of whether the fence is working or not! (However, one site manager
checks if the voltage is OK by pushing the live wire onto the ground with a large pebble. If there is a
large spark the fence is deemed to be working!). A standard Digital Electric Fence Tester (Electric
Fence Volt Meter) will display and measure accurately up to 9900 volts (9.9kv) and costs around £40.
First check the voltage of a new fence to give a baseline against which future checks can be
compared; if the voltage drops it will signify a problem. Check the voltage at the furthest point from
the energiser; some drop in voltage, say 1500 to 2000v, is normal. A drop of more than 2000v
means that either the energiser is underpowered for the fence, or that vegetation or something else
is ‘loading’ the fence (touching it and causing voltage to leak away), there is a short-circuit
somewhere in the system or a combination of both. If the base voltage of the newly built fence is
6000v or better then everything is working OK.
On subsequent checks, watch for an overall voltage drop of 1500v or more. Such a significant
decrease means it is time to check for problems and correct them before the predator discovers the
fence no longer packs a punch. (Note: It is normal for voltage to be 500-1000 lower in the morning
when moisture on the fence, posts and nearby vegetation, which can cause temporary current
leakage.)
A short in an electric fence occurs when the power escapes to the ground. This can be caused by a
broken underground cable, a broken wire or insulator, a loose connection, or something touching
the fence, such as excessive vegetation.
How to check the voltage of an electric fence with a Digital Voltmeter
First attach the digital voltmeter to the fence line, moving it laterally to get a good contact, and then
push the probe into the ground. The voltage reading will be displayed on the screen. On a good
electric fence line this should be in excess of 6,000 volts (Note: it should be over 3000v even at the
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furthest end of the fence line from the energiser.) If the voltage is just slightly below normal, say
5,000 volts, then there is probably a minor fault caused for example by light vegetation touching the
wire. However, if the reading is substantially lower, then a major fault exists.
To find the fault, move along the fence line, taking readings every 100 metres or so. As a rule of
thumb, the voltage will drop roughly 100 volts every 100 metres in the direction of the fault and will
then level out once the fault is passed. If the fault is not obvious, then sections of the fence can be
isolated systematically using cut-out switches, making it easier to locate a problem. Once the
problem area is located, individual wires may have to be isolated to pinpoint the fault.
Finding a fault using a Fence Doctor or Fault Finder
An electric fence diagnostic tool and fault locator (Fence Doctor or Fault Finder) measures both
current and voltage. This helps troubleshoot fence repairs by pointing in the direction of the fault
and costs c £105. One such tool is The Speedrite Remote with Fault Finder, which can turn a
compatible Speedrite energiser on or off from anywhere along the fence line.
Start taking readings with the Speedrite Remote with Fault Finder (Fig. 36) near the energiser's lead-
out wires. Then move down the fence line following the arrow away from the energiser, taking
readings at regular intervals and at any junction point. The previous reading is shown briefly in the
top right corner of the screen so that readings can be compared. If the current reading suddenly
falls, you have gone past a fault. Retrace your steps to find the fault. Note that after a few seconds
the previous current reading will be replaced with the present voltage reading (kV).
Fig. 36. Finding a fault in an electric fence using the Speedrite Remote with Fault Finder.
Fence maintenance Red foxes are 'surplus killers' and can cause immense damage quickly. Lack of regular maintenance
is the main cause of fence failure. Maintenance requirements will be minimised if the fence is
meticulously constructed with high quality materials at the outset.
In a study of predator exclusion fencing for areas of high conservation value in Australia (Long and
Robley 2004), the average time per week spent maintaining predator exclusion fencing, including
fence checking, was 0.9 hrs/km of fence (Table 13). To provide easy access for fence inspections and
maintenance, a vehicle track should be cleared on at least one side of the fence.
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Table 13. Average time per week spent maintaining Australian predator exclusion fences (Long and Robley 2004)
Time spent/km of
fence (hours)
Number of
cases (%)
0.01 – 0.5 6 (40)
0.51 – 1.0 3 (20)
1.01 – 1.50 4 (27)
1.51 – 3.0 2 (13)
Average 0.9 hrs/km
Common fence maintenance problems requiring remediation Regular inspection and maintenance should not only include voltage checks but also the integrity of
the fence itself, including posts.
Problems include: fence posts across undulations that may have pulled up, fallen branches on the
fence following gales, broken insulators (which must be replaced) and slack live wires touching the
mesh fence or earth wire causing a ‘dead short’ rendering the fence inoperative. To prevent this
high tensile or braided steel line wires can be tensioned with cotton reel or ratchet type strainers.
Other common problems seen on RSPB reserves in the past 12 months are:
Distorted mesh that needs pulling back into shape to return it to the original specification (8cm
width rather than 14cm in the example below).
Breaks in the wire mesh. This is usually a result of over enthusiastic brush cutting of low vegetation
by volunteers or assistant wardens. In the example below this was the obvious route that a fox used
to access the fenced area as evidenced by a fox trail leading to the fence, prints inside and out and
fox hair on the wire. To prevent this it is safer to use a strimmer and heavy duty nylon cord rather
than a metal brush cutting head.
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Brash or blown rubbish (particularly if containing metallic material) against the fence causing
electric wires to short or facilitating access by mammalian predators.
105
Vegetation touching the fence and causing electric wires to short out. Any vegetation that is
touching or getting close to vegetation must be controlled before it touches a conducting wire(s).
This is best achieved by strimming around the base of the fence or by killing off the vegetation with
an approved herbicide (with repeat applications as necessary).
Note that if the fence is within a SSSI, consent from Natural England (NE) will be required or, if the
anti-predator fence is within 2 meters of a watercourse, a derogation will be required from the
Environment Agency to apply herbicide to the fence line. At Dungeness, either end of the area
within 2m of the watercourse is marked with posts to warn the operator not to spray between them.
Detecting the presence of foxes inside an anti-predator fence Once an anti-predator fence is erected and activated, the area inside the fence should be checked
regularly for the presence of mammalian predators that have penetrated the fence or were enclosed
by it. This can be done by looking for scats, footprints (in soft ground or after snow or by the
installation of bespoke tracking plots), trail cameras (e.g. at a bait station or vulnerable points of the
fence such as gateways) or by at least weekly checks during the breeding season with night vision
equipment (e.g. an image intensifier or thermal imager). To increase the chances of detecting the
presence of a predator, it is usually best to employ a combination of techniques. In addition,
monitoring the nest success or breeding behaviour of the target species (e.g. by the use of nest
cameras, temperature data loggers in the nest or observation of known nests) can quickly reveal if
something is amiss.
More information on methods used to detect the presence of large mammalian predators is given in
Appendix 8.
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Chapter 11. Effects of anti-predator fences on non-target species All site managers considering the installation of predator exclusion fences should be aware of the
potential effects on non-target species, some of which may not have been foreseen.
Predator exclusion fences can, by their very nature, restrict movements of other large mammals
such as hares. In fencing trials to protect crops against badgers undertaken by MAFF, excluded
badgers were found to forage on alternative crops close to the protected area. At Otmoor, farmers
of land adjacent to the reserve voiced concerns that any increase in the area from which predators
are excluded would result in increased badger activity on their land increasing the risk to their cattle
of bovine TB infection.
Erecting small-mesh fences to limit predator movements can result in negative side-effects for other
wildlife that find them impassable, for example ducklings (Pietz & Krapu 1994). In the Western Isles
similar fences to those used to exclude hedgehogs, designed to keep rabbits from crops, can restrict
the movements of ducklings and wader chicks, and even lead to their death if they become
separated from parents or entrapped in the netting (D. Jackson, pers. obs.). Redshank chicks are
likely to be at particular risk because they commonly travel long distances (up to 1·5 km) between
feeding areas (Jackson 1988). Such negative side-effects can be minimized by careful choice of
fence-lines, making exclosures relatively large and using the largest mesh size consistent with
excluding the target predators, so that wader chicks can pass through.
At several sites, frogs have died from multiple shocks from electric strand fencing. Careful
consideration should be given to the erection of electrified strand fences or mesh netting near
waterbodies containing frogs, toads and newts (especially natterjacks and great crested newts which
have special protection under the Wildlife and Countryside Act 1981 and the Conservation (Natural
Habitats) Regulations 1994). Hedgehogs are also prone to electrocution by electrified strand or
netting fences. To prevent such electrocutions, a low physical barrier can be installed in front of the
electric fence or the bottom live fence wire can be disconnected.
Birds that may collide with fences, especially the top strand of electrified strand fences include
swans and geese. Deer can also become entangled and damage themselves. To reduce bird strike
risk or to deter deer from trying to jump over, the top strand can be marked at intervals with twists
of white electrical insulating tape.
Non-target species may also benefit from the protection provided by the fence, which can have
adverse consequences. Feral geese nesting inside the fence can have very high productivity leading
to an increase in their numbers to the extent that they become a potential nuisance to other birds
try to nesting within the fence (e.g. greylags at Otmoor, barnacle geese at Minsmere). Lesser black-
backed gulls from Havergate Island have settled to nest on the scrape at Hollesley presumably
because of the protection from ground predators afforded by the fence.
Increased density of the target species within the fenced area often attracts aerial predators e.g.
kestrels predating little terns, red kites predating lapwing chicks. Potential solutions are diversionary
feeding or to move the target species around an area by the use of temporary fencing, changing the
area protected between years.
107
In theory, another potential problem might be ‘meso-predator release’: whereby excluding one
potential nest predator(s) might allow another predator species not excluded by the fence to
increase within the fenced area e.g. mustelids.
Badger gates If a badger(s) is found within an anti-predator fence there is an obligation to allow it to 'escape'
unharmed. For this reason, if badgers are being excluded by a barrier or combination fence it is wise
to install one-way badger gates (Fig. 36) to enable badgers trapped within the fence to make their
own way out.
Fig. 36. A standard Tornado badger gate.
At Minsmere, four off-the-shelf Tornado badger gates ( http://www.tornadowire.co.uk/fencing-
gates-posts ) were installed in the 2km combination fence, with a view to installing more if they
were needed. Once staff were confident that there were no badgers or foxes inside the fence, the
gates were securely fastened shut, just in case a badger or other mammal was to find a way of
opening them from the 'wrong' side (Adam Rowlands pers comm.). If a badger did penetrate the
fence, the gates would be unfastened. It remains to be seen if a badger did get through the fence
whether it would escape via a gate or just exit the fence by the route they breached it. .
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References Acorn, R.C. and Dorrance, M.J. 1994. An evaluation of anti-coyote electric fences. University of
California.
Coman B. J. and McCutchan J. 1994. Predator Exclusion Fencing for Wildlife Management in
Australia. A report to the Australian Nature Conservation Agency.
DEFRA. The red fox: management in rural areas. Rural Development Service Technical Advice Note
43.
Forster, J.A., 1975. Electric fencing to protect sandwich terns against foxes. Biological Conservation
7: 85
Gulickx M.M.C., Beecroft R.C. & Green A.C. 2007. Creation of a ‘water pathway’ for otters Lutra
lutra, under an electric fence at Kingfishers Bridge, Cambridgeshire, England. Conservation
Evidence, 4, 28-29
Jackson, D.B., 1999. Report on the 1998 Hedgehog Exclosure Trials and recommendations for the
role of fences in Uist wader conservation. RSPB Research Department.
Jackson, D. B., 2001. Experimental removal of introduced hedgehogs improves wader nest success in
the Western Isles, Scotland. Journal of Applied Ecology, 38: 802-812.
Koenen, M.T., Utych, R.B., and Leslie Jr., D.M, 1996. Methods used to improve least tern and snowy
plover nesting success on alkaline flats. Journal of Field Ornithology, 67 (2): 281-291.
Long, K., and Robley, A. 2004. Cost effective feral animal exclusion fencing for areas of high
conservation value in Australia. Arthur Rylah Institute for Environmental Research
Department of the Environment and Heritage, 2004
Lloyd, H. G. 1980. The red fox. Batsford London. 320pp
McKillop, I.G., Pepper, H.W., and Butt, R., 1999. Electric fencing reference book. Produced for
DEFRA.
Minsky, D., 1980. Preventing fox predation at a least tern colony with an electric fence. Journal of
Field Ornithology, 51: 180-181.
Moseby, K.E. and Read, J.L, 2006. The efficacy of feral cat, fox and rabbit exclusion fence designs for
threatened species protection. Biological Conservation, 127 (4): 429-437.
Natural England Technical Information Note TIN027. Badger problems: use of electric fencing to
prevent agricultural damage.
Natural England. The red fox in rural areas. Species Information Note SIN004. Available at
http://www.naturalengland.org.uk/conservation/wildlife-management-
licensing/leaflets.htm
O’Brien, 2002. Fact Sheet: Fencing Options in Predator Control. Ontario, Ministry for Agriculture.
Patterson. I.J. The control of fox movement by electric fencing. Biological Conservation 11:267-278.
Poole, D.W., and McKillop, I.G., 2002. Effectiveness of two types of electric fences for excluding the
Red Fox (Vulpes vulpes). Mammal Review, 32 (1): 51-57.
Robley A., Purdey D., Johnston M., Lindeman M., Busana F., and Long K. 2007. Experimental trials to
determine effective fence designs for feral cat and fox exclusion. Ecological Management &
Restoration 8:193-198.
Schifferli, L., Spaar, R., and Koller, A., 2006. Fence and plough for Lapwings: Nest protection to
improve nest and chick survival in Swiss farmland. Osnabrucker Naturwissenschaftliche
Mitteilungen, 32, S. 123-129.
Schreder, P.T., undated. Fencing against predators. Oregon State University, Albany.
109
Sexton D. (1984) Electric fence policy. Working party report to the Minister for Conservation, Forests
and Lands the Hon. R. A. MacKenzie, M.L.C., Victorian Department of Conservation, Forests
and Lands.
Smith, R. K., Pullin, A. S., Stewart, G. B., & Sutherland, W. J. (2010). Effectiveness of predator removal
for enhancing bird populations. Conservation Biology, 24, 820–829.
Trout, R.C & Liles, G. 2005. The use of fencing to prevent access by otters to fisheries. A report to
the Environment Agency & SAA.
United States Department of Agriculture (USDA). 2005. Managing urban/suburban coyote problems.
Nevada.
Wade, D.A., 1982. The use of fences for predator damage control. Texas Agricultural Extension
Service.
Washington County Soil and Water Conservation District (SWCD) and the Small Acreage
SteeringCommittee, 1999. Fact Sheet: Designing a Fence, Tips for Small Acreages in Oregon.
Woodland Trust, Specification No. 3.11, Fencing 1.9m deer-proof. Available at
http://www.woodlandtrust.org.uk/communitywoodlandnetwork/publications/documents/S
pec%203-11.pdf
Acknowledgements Many people kindly provided information included in this guide. Particular thanks are due to Keith
Ballard, Dave Blackledge, Tim Fisher, Andrew Gouldstone, Al Grubb, Ian Hawkins, Richard Humpidge,
Andy Kearsey, Rob Lucking, Lee Marshall (WWT), Richard Miller, Julian Nash, Andy Needle, Harry
Paget-Wilkes, Tommy Pringle, Jon Reeves, Brad Robson, Jim Rowe, Jim Scott, Jen Smart, Mark Smart,
Jamie Smith, Mark Whiffin, David Wilding and Barry Yates (Sussex WT).
Mel Kemp, Andy Needle, Tommy Pringle, Graham White, David Wilding and Barry Yates made
improving comments on specific sections or all of the manuscript. I am grateful to them all.
110
APPENDIX 1. Appropriate fence types for different species for which anti-
predator fences can increase nesting success or productivity
Target species for which anti-predator fences have been successful at increasing nesting success or
productivity in the UK are wet grassland and machair waders nesting at high density, softshore
seabird colonies (e.g. terns nesting on shingle banks, dunes or small islands), avocets and other
waders breeding at coastal lagoons), rare ground nesters breeding at high density or individual nests
and their immediate surroundings (e.g. stone curlew, curlew, black-winged stilt, Montagu’s harriers).
The appropriate circumstances and type of fence are described below.
Wet grassland breeding waders Sites with significant* or potentially significant numbers of waders breeding but with low
productivity due to fox, badger or possibly hedgehog predation are potential candidates for predator
exclusion fencing.
(*The Dutch consider 50 pairs of a breeding wader species to be a viable (meta-) population).
Breeding waders can be protected by semi-permanent (combination, barrier or electric strand)
fences and temporary (strand) fences (see below). To make the installation of expensive semi-
permanent combination fencing worthwhile, sites should hold a significant number of breeding
waders every year.
As a minimum, the best breeding wader area(s) should be fenced, ensuring that there are suitable
areas for both wader nesting and feeding (chick rearing) within the fenced area. Depending on the
proportion of the available suitable habitat within the fenced area, expending additional effort on
fox control could be worthwhile and this will also help to reduce ‘pressure’ on the fence from foxes
(see later).
Although, semi-permanent fences usually work well, they can create a prey ‘hot spot’, making the
wader chicks vulnerable to predation from aerial predators. The chances of this could be reduced by
the use of temporary/portable electrified wire strand fences enabling ‘the protection’ to be moved
around between years. Also, a temporary/portable strand fence may be the only option at sites
subject to regular seasonal flooding.
Soft shore seabirds The choice of fence type will depend on colony importance and site fidelity. For colonies that are
prone to move around or are publically accessible, temporary fences are the best option. The exact
configuration of the fence will depend on whether the protection is mainly against foxes or badgers
(see below).
For islands in waterbodies that are used regularly by colonially nesting terns or gulls, barrier fencing
around the individual island(s) can be the best and most cost-effective option. However, these can
be more unsightly than a barrier or combination fence installed around the whole waterbody.
Avocets and other waders breeding at coastal lagoons Significant populations suffering high predation from ground predators are best protected by a fence
around the whole lagoon rather than around individual islands. This allows free-movement of chicks
between the best feeding areas and will be less unsightly than fencing islands individually. Usually,
the best option is a barrier or combination fence (to deter foxes and badgers). If the target birds
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move around between years, installing a temporary strand electric fence against foxes after the
target species has settled may be the best option.
Stone-curlews and individual nests/pairs of other rare ground nesters Sites with a high breeding density of the target species (e.g. stone curlews nesting on heathland),
where mammalian predation is known to be a major contributory cause of low productivity (for
stone curlews defined as <0.61 fledged chicks per pair) can be protected with a combination fence.
Alternatively, where combination fencing is not possible, individual nests and their surrounds can be
protected with temporary electric fencing e.g. around rotational fallow stone-curlew nesting plots
within grassland or arable. A fence can even be installed after the birds have laid (see later).
In both The Netherlands and Eastern England, individual nests of Montagu’s harriers nesting in crops
are routinely protected from fox predation by a small barrier fences installed around them just after
hatching.
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APPENDIX 2. The evidence base for fence design against specific predator
species
Foxes No fence is totally effective against foxes and site managers must be vigilant to detect those that
enter fenced areas and eliminate them quickly (foxes are 'surplus killers' and can cause significant
damage in a short time period). Designing a barrier to exclude foxes is particularly challenging owing
to their climbing agility, jumping and digging capability and capacity to learn how to overcome
obstacles.
Foxes are capable of jumping to a height of 1.8 m ((Day and MacGibbon 2002) and have been
observed leaping over fences exceeding 1.3 m high (Coman and McCutchan 1994; D. Wilding pers.
comm.). However, usually foxes try to 'scramble' over fences not to jump over them. They readily
scale chain mesh fences over 2 m high (Coman and McCutchan 1994), utilising any solid support to
brace their climb and have been observed hanging upside-down from the ceilings of wire mesh
enclosures (see below).
Although capable of digging, this does not appear to be their preferred method of breaching fences
(Poole and McKillop 2002). Instead, foxes more frequently capitalise on holes under the fence that
have been at least partially dug by other animals such as rabbits. They are also quick to exploit weak
points in the netting, including small holes or gaps in joins (Poole and McKillop 2002; Long and
Robley, 2004).
Foxes will refrain from traversing electrified fences under most circumstances. Poole & McKillop
(2002) tested two electric fences against captive foxes; the first being a design with the
recommended specifications for strained wire (McKillop et al. 1999) and the second a netting fence
105cm high. Both fence types were crossed only during times when the captive foxes were under
greatest stress (i.e. when staff were inside the enclosure).
McKillop et al (1999) recommend using eight high-tensile wires from ground level to 105cm,
alternating live and earthed wires prevent foxes from jumping straight through the fence. However,
to exclude badgers they recommend using a fence with 4 live wires at heights of 10, 15, 20 and
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30cm. This means that for sites where both foxes and badgers are a problem, stranded electric
fences would not be suitable, because the specifications for each species are different. Either fence
design of wire strands would be less effective against the other species.
Coman and McCutchan (1994) recommend a wire spacing for foxes of 70 – 90 mm, but also found
during trials with dead foxes that even a spacing of just 75 mm did not guarantee an animal with dry
fur would receive a shock when passing between electrified wires.
Foxes can be wary of electric fencing, with relatively low fences deterring the majority of foxes in
some situations. In Scotland, Patterson (1977) trialled a 45cm high 3-stranded electric fence across a
peninsula to prevent foxes disturbing or predating nesting sandwich terns and eider ducks. The
fence could not be extended onto the intertidal area at either end because it would be short-
circuited at each high tide. The fence was removed in August when nesting had finished. The
electric fencing although not fox-proof reduced overall fox visits to less than a third of their former
frequency. No foxes were observed crossing this fence in the first season, although 7% and 25% of
encounters resulted in breaches in the second and third seasons respectively and an increasing
number of foxes passed around the seaward ends of the fence.
Although foxes refrain from crossing electrified fences under most circumstances, they will breach
fences given sufficient motivation and their capacity to learn how to negotiate obstacles. In
Australia researchers found that foxes quickly learnt to cross fences constructed with various
arrangements of offset electric wires. The ability of foxes to breach fences is enhanced by their
persistence at doing so. Even after receiving electric shocks, foxes will continue to investigate the
fence (Poole and McKillop 2002). Consequently, as soon as a weakness in a fence occurs, whether it
is due to a construction flaw or irregular fence maintenance, foxes will be ready to exploit it.
Even if specifically designed to deter them, strand electric fences are probably the least effective
type against foxes because a fox's fur is such a good insulator. This makes the mechanical design of
the fence more important. It therefore may be wise to invest in barrier fencing, which would also
exclude badgers. A combination fence (see below) should prevent both foxes and badgers entering
an area, by acting as a barrier to the badgers, but having the electric strands to deter foxes. These
usually comprise one or more electric strands at the top of the barrier and an additional offset wire
outside the fence. These provide additional protection as the nose or feet of the fox are likely come
into contact with the wire if a fox tries to climb or jump the fence. Plastic netting and anything less
than 1mm gauge wire netting e.g. chicken wire and low gauge welded mesh is unsuitable for
excluding foxes as they can chew through it (Poole and McKillop 2002). The image below shows the
damage to 16 gauge mesh done by a vixen while escaping from a rehabilitation pen.
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Foxes have an average skull width of 82 mm (Loyd 1980) and, given that their shoulder width is not
much greater than this, it has been surmised that if a fox can get its head through a hole it can
probably get the rest of its body through (Coman and McCutchan 1994). At a site in the United
Kingdom a young fox was observed squeezing through a 70 mm gap between a gate and its post.
The skull of a fox shot at Marshside RSPB reserve, which measured 96mm (i.e. way over the mean
width), passed easily through the standard 8cm wide mesh of the reserve’s combination fence if
turned sideways (A. Grubb pers comm.). The fox appeared very slim bodied and was suspected of
penetrating the fence, although it was not seen inside it. Against this, foxes have never been known
to penetrate fences of the same specification elsewhere e.g. Otmoor (D.Wilding pers comm.).
On their own (i.e. without the use of electric wires), rigid overhangs that extend as a horizontal or
angled projection from the top of a fence, provide a challenging but not impassable barrier to foxes.
In Australia, a fox was observed scaling a 1.8 m fence and climbing upside down along the under-
section of a 300 mm horizontal overhang.
Most overhangs are used in conjunction with electric wires and these appear to be considerably
more effective. However, a 180 cm high wire netting fence with a horizontal foot apron to prevent
digging underneath the fence and a curved ‘floppy’ overhang proved effective in intensively
monitored paddock-scale exclosures. The overhang proved most effective when it was bent to form
a rounded arc rather than a 45° straight overhang. The floppy top must be 600 mm in length,
enabling it to form a full semi-circle.
Although foxes are capable of jumping to heights of approximately 1.8 m they are most likely to
jump onto a fence at lower heights (1.2 –1.5m). Foxes seem not to attempt to jump or climb the
1.2m high fences surrounding Montagu’s harrier nests, perhaps because the area enclosed (2-4m in
diameter) is so small.
Before installing a fence to exclude foxes, it is wise to just check the perimeter of the planned fence
and 'think like a fox' to make sure there would be no easy access points or things to climb onto
(including low trees).
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Often when fences are installed they enclose one or more foxes inside the protected area! Lethal
control by shooting is usually the best way of removing them. (In Australia poison baits are the usual
method!)
Badgers At sites where they are the significant nest predator, badgers can be excluded by barrier fences or
electric strand fences.
To prevent access by badgers, barrier fences should comprise strengthened heavy gauge fence
netting such as chain-link, weld-mesh, or similar with a mesh size no greater than 8cm. 18 or 19
gauge rabbit netting or 'chicken wire' is not strong enough. Badgers are good climbers, so where a
free standing barrier fence is used, it is best to incorporate a supported overhang at the top,
directed away from the area to be protected. The fence should be at least 125 cm high and be
buried to a depth of 60 cm. Alternatively, the mesh can be folded outwards on the ground surface
for 40-50 cm to deter badgers from digging beneath the fence.
The recommended design of electric strand fences to exclude badgers should comprise four
electrified parallel conducting wires at heights of 10, 15, 20 and 30cm above the ground (McKillop et
al., 1999). The wires, which are all live, are held by adjustable plastic insulators supported on metal
stakes. The stakes can be placed up to 10m apart, although ground undulations may dictate closer
spacing. Where the fence line bends, wooden anchor posts should replace the normal metal stakes.
The whole system is tensioned at a reel post placed at the end of the fence.
Both steel wire and polywire fences, maintained at 6 kV, are effective at excluding badgers.
However, steel wire is the most effective conducting material and may deter badgers at a lower
voltage (4 kV) than polywire (6 kV) (MAFF 2001). Steel wire is also more durable than polywire,
tensions over greater distances and can carry a higher voltage.
Badger fencing requires, at least, a 1.5J energiser, preferably mains powered or, where this is
impractical, connected to a 12V battery. To maintain effective badger deterrence, the fence voltage
should not fall below 4kV (MAAF 2001).
When a badger encounters a fence for the first time it approaches cautiously before investigating,
usually with its nose, which is poorly insulated and highly innervated. Badgers observed to touch
electrified wires generally respond by retreating immediately away from the fence (Poole &
McKillop. 1999). This response is most marked when a badger touches an electrified wire with its
nose. This pronounced flight behaviour contributes to the effectiveness of electric fencing as a
management tool for badgers. Badgers do not appear overly stressed by the receipt of an electric
shock but usually exhibit conditioned avoidance and avoid electric fences for periods of up to six
weeks after receiving a shock (Poole & McKillop, 1999).
Badgers observed trying to penetrate an electrified strand fence usually step slowly between the
upper wires of the fence. They almost always complete the crossing and show no sign of having
received a shock. This suggests that badgers receive only a mild shock when crossing in this way.
However, as noted above in field trials with high tensile steel strand fences operating at voltages of 6
kV, no badgers penetrated the fence (MAFF 2001).
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Surprisingly, digging under electric strand fences is not a serious problem. Badgers digging under
electric fences has rarely been recorded. Presumably, receiving shocks deters badgers from
spending the time required near to the fence to dig under it. A single strand of barbed wire pegged
to the ground at intervals immediately beneath the electrified wires also deters badgers from
digging under them (L. Marshall pers comm.)
At sites where both foxes and badgers are a problem, stranded electric fences are less suitable,
because the recommended specification for foxes is different (see above). In this situation it is best
to invest in a combination fence. A combination fence should prevent both foxes and badgers
entering an area, by acting as a barrier to the badgers, but having the electric strands to deter foxes
(see later).
Cats A feral cat will first assess the base of a fence. Feral cats can jump over a barrier of 1.5 m
(Hitchmough 1994; cited in Karori Wildlife Sanctuary Trust Inc. 1998) and are capable of jumping to
heights of approximately 1.8 m (Day and MacGibbon 2002). However, like foxes, cats are most likely
to jump onto the fence at lower heights (1.2 –1.5 m, Moseby and Read 2006). Cats are also capable
of jumping further up vertical netting from their original landing spot (Day and MacGibbon 2002).
This means that if fence corners have internal angles of less than 120 degrees, cats are able to leap
up and across to adjacent fence panels, increasing their chance of getting over the fence (Day and
MacGibbon 2002). Also, cats readily climb any solid structures that they can gain purchase on, like
wooden fence posts (Moseby and Read 2006). To prevent cats securing purchase on the posts it is
better to use metal posts or clad wooden posts with corrugated roofing iron nailed to them. A
minimum 50 mm mesh size is required to exclude juvenile cats (Day and MacGibbon 2002).
Cats are wary of climbing unstable surfaces such as loosely tensioned, floppy netting (Day and
MacGibbon 2002). This type of netting can be an effective barrier to climbing animals, including
cats, by denying them stable climbing footholds (Coman and McCutchan 1994). To be effective such
fences should have a floppy top at least 600 mm wide enabling it to form a full semi-circle. A floppy-
topped fence without electric wires has successfully excluded foxes and cats from a 6000 ha reserve
in Australia (see section on Barrier Fencing below). On their own (i.e. without the use of electric
wires), rigid overhangs that extend as a horizontal or angled projection from the top of a fence,
provide a challenging but not impassable barrier for feral cats (and foxes).
Trials conducted in captivity have shown that individual feral cats react differently to receiving
electric shocks, with some retreating from the electric wire and avoiding contact with it in the future
(Moseby and Read 2006) and others becoming almost frenzied, resulting in a more vigorous, and
often successful, attempt at crossing the fence (Day and MacGibbon 2002, Moseby and Read 2006).
Cats in the latter group sometimes withstand multiple electric shocks in the process.
The use of electric wires to dissuade cats from climbing fences has had variable success. Electric
wires without an effective physical barrier, or wires placed at the end of an overhang are ineffective.
The addition of electric wires proved useful during pen trials but only when the 600 mm ‘floppy’
overhang forced feral cats to pause long enough to receive an electric shock. The electric wires were
placed at heights of 1200 and 1500 mm, equivalent to the heights most cats first jumped to, which is
also where cats position themselves when attempting to negotiate the floppy top. Cats were able to
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squeeze between the fence and offset electric wires that were spaced further than 80 mm from the
body of the fence without receiving a shock.
Hedgehogs The use of electrified ‘polywire’ mesh netting or electric strand fencing for excluding hedgehogs is
not recommended on animal welfare grounds because hedgehogs can become entangled and suffer
repeated electric shocks. However, a vertical barrier of taut chicken-netting (30mm mesh, 0·45m
high) was successful at excluding hedgehogs on South Uist (Jackson 2001). The fence also had an
electrified polywire offset 80mm from the upper high-tensile wire on the outer side, but there was
no evidence that this was needed to prevent hedgehogs climbing over, although it was effective at
stopping damage by livestock.
Otters Trout & Liles 2005 state that otters cannot penetrate high tensile mesh of 75mm square, but trail
cameras have shown that otters can get through the 8cm mesh fence around the Scrape at
Minsmere. The skull width of juvenile otters is 64mm (female) - 69mm (male). Therefore, a 5cm
mesh fence will keep out most otters. 5cm netting (e.g. Tornado Otter Fence with a mesh of 100mm
x 50mm) is a proven barrier but is more unsightly and 60% more expensive than the standard 7.5 -
8cm horse netting that will keep out most foxes.
Adult otters can climb over and dig under fences. Even a 1.5 m high vertical fence can be crossed by
a determined individual. A dog otter can reach to the top of a 0.9m fence without using the front
paws to climb. The top 500mm of the fence should be cranked outwards and/or an off-set
electrified wire to prevent an otter from climbing the fence (Trout & Liles 2005).
To prevent otters from digging underneath fencing, at least 50cm should be buried into the ground
or turned outwards either buried or at ground level. Lapping 50cm of mesh wire on the surface is
much cheaper than digging trenches unless a netting plough machine is used.
‘Stand-alone’ multiple parallel strand electric fences against otters are also widely available (e.g.
from Rappa), but there is little information on their effectiveness. All the strands can be live as
otters are heavy enough to give an earth. At least 5Kv should be registered on the fence.
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APPENDIX 3. How Electric Fences Work (http://www.Rappa.co.uk)
An electric fence is based on three main components:
- an energiser to generate regular pulses of electrical current
- the fence wire to conduct the current
- an earthing system to return the current back to the energiser
The energiser sends brief, high voltage pulses of electrical current down the fence line. When an
animal touches the wire, its body closes the circuit, allowing the electricity to flow down to the
ground and back to the energiser. The pulse only lasts for a fraction of a second, so the animal only
feels a very brief shock, and moves away from the fence immediately.
An electric fence is really a psychological barrier, so you can use fewer materials than a physical
barrier, keeping cost to a minimum. It is also completely safe – animals dislike the sensation,
deterring them from approaching the fence in the future. Most animals will receive a shock within
the first week of the fence being erected; from then on they will avoid it.
An electric fence consists of a number of essential elements:
Reel
A reel allows you to unroll the fence wire evenly without creating potentially damaging kinks, and
roll it up again neatly for reuse. By locking firmly onto a reel post, the reel also keeps the fence wire
taut.
Posts & Stakes
While permanent fences use timber posts to hold the fence wire, temporary fences use metal or
plastic stakes, with more substantial anchor posts at the beginning and corners to take the strain.
Temporary fences also require a reel post at the end of the fence line to hold spare fence wire
firmly, and keep the line taut.
Insulators
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Insulators stop the fence wire touching the post or stake, so the electricity doesn’t leak back to the
ground. Anchor or end-strain insulators also take the strain of the wire at the end of the fence line or
at corners. Polystakes, made of non-conductive plastic, do not need separate insulators.
Good quality insulators should be smooth, and dry easily to prevent moisture collecting in nooks or
cracks – otherwise the current can leak in an ‘arc’, which can be heard as a regular clicking sound.
Arcing reduces the effectiveness of the fence.
You can use offset insulators to hold an electric fence wire a short distance away from a new or
existing permanent fence. The wire stops animals causing damage by biting the fence, or leaning or
rubbing against it, and helps a timber or wire mesh fence last longer.
Earth Stake
To work effectively, all electric fences have to be properly earthed. Earth stakes are inserted into the
ground and attached to the energiser, and ensure the power returns through the ground and back to
the energiser when an animal completes the circuit by touching the fence.
Fence Tester
All electric fences need regular maintenance, so you need a device to measure the power on the
fence lines. A fence tester or voltmeter, will help you locate any problem areas where power is
leaking away.
Energiser
The powerhouse of the electric fence. The energiser converts electricity from the mains supply or a
battery into regular high voltage pulses of electric current that travel along the entire length of the
fence. Each pulse only lasts for a fraction of a second, and is produces a roughly one second
intervals.
The type of energiser you need depends on how close the fence is to a mains supply, how long the
fence will be, and the kind of animals you want to control.
Conductor (Wire)
You can use various types of wire, or conductor, for an electric fence. Steel wire, either single or
multi-stranded, is strong, durable and highly effective at conducting electricity, so the animal
receives a greater shock when touching the fence. However, steel wire is heavier than other
alternatives, and best used in permanent or semi-permanent fencing.
A lighter alternative is polywire - UV-stabilised polythene twine with three or more strands of
stainless steel wire woven into it. Polywire is designed for temporary fencing and strip-grazing,
although the more substantial polyrope can be used for permanent fencing.
Polytape and polybraid consist of stainless steel wires and polythene strands woven into a ribbon,
and come in a range of widths and colours. Both are highly visible, though more vulnerable in high
winds, and can be used for permanent and temporary fencing.
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Electrified netting is made a range of mesh sizes for different animals. The horizontal strands are
polywire, while the vertical strands are plain polythene twine. It is most suitable for temporary
fencing and strip-grazing.
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APPENDIX 4. Major fence manufacturers, stockists & contractors
Agrisellex Electric Fencing Ltd: www.agrisellex.co.uk
Agrar Horizont: https://agrar.horizont.com/en/
Countryside Fencing Ltd: www.countrysidefencing.com/
Flexinet: available through several fencing websites
Gallagher Electric Fencing: http://www.gallagher.eu/en_gb
Hotline Electric Fencing: http://www.hotline-fencing.co.uk/
H S Jackson & Son (Fencing) Ltd: http://www.jacksons-fencing.co.uk/
Mesh Direct: http://www.meshdirect.co.uk/
Rappa Fencing: http://www.rappa.co.uk/
Speedrite Electric Fence Systems: https://www.speedrite.com/ The electric-fence.co.uk: https://www.electric-fence.co.uk/
Tornado Wire: http://www.tornadowire.co.uk/
Uniwire: Quality British Fencing Products http://www.uniwire.co.uk/
UK Tapes Ltd: http://www.tapesandmesh.com
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APPENDIX 5. RSPB reserves employing an anti-predator fence(s) up to 2017.
Reserve Fence type Status Power Target species Ha protected Length (km) Contact
Arne Moors Strand Semi-permanent Battery LWG waders 21 2.2
Beckingham Combination Permanent Battery LWG waders 18 2.1 Joe Harris
Beckingham Combination Permanent Battery LWG waders 10 1.3 Joe Harris
Belfast Lough Combination Permanent Mains Waders, terns 13.5 c.1.2 Chris Sturgeon
Berney Marshes Strand Temporary Battery LWG waders
Jim Rowe
Brading Marshes Strand Temporary Battery LWG waders 5.5 1km Keith Ballard
Cattawade Combination Permanent Battery LWG waders 16.2 0.8 Jon Rapley
Cavenham Combination Permanent Mains Stone curlew 65 2.36 Dave Rogers
Cliffe Marshes Netting Temporary Battery B-w. stilts Dearne Valley Strand Semi-permanent Mains LWG waders
Dave Waddington
Dee Estuary (IMF2) Combination Permanent Mains LWG waders
Graham Jones
Dungeness Combination Permanent Battery Lapwing 14.14 2.9 Craig Edwards
Exe (Powderham) Strand Semi-permanent Battery Lapwing 20 2
Exe (Exminster) Strand Semi-permanent Battery LWG waders 18 1.8
Fen Drayton Barrier (floating) Semi-permanent
Gulls, terns
Tim Fisher
Great Bells Farm Combination Permanent Battery LWG waders 110 4.3 Julian Nash
Greylake Strand Temporary Battery then mains
LWG waders 50ha then 100ha
3.5k then 5.5k Harry Paget-Wilkes
Greylake Combination Permanent Mains LWG waders 100 5.5km Harry Paget-Wilkes
Hodbarrow Barrier (welded mesh)
Temporary n/a Terns 0.2 0.09 Dave Blackledge
Hodbarrow Barrier (adapted security fence)
Permanent n/a Terns 1.7 0.4 Dave Blackledge
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Hollesley Combination Permanent Battery Avocet 18 1.8 Aaron Howe
Langstone Harbour Strand Temporary
Gulls, terns
Wez Smith
Leighton Moss Strand Temporary Battery Gulls, avocet ? ? Richard Miller
Loch Leven Combination Permanent
LWG waders
Vicky Turnbull
L.L.Erne (Rosscor) Combination Permanent Battery LWG waders 4.2 0.61 Brad Robson
L.L.Erne (Muckinish) Combination Permanent Battery LWG waders 5.25 0.41 Brad Robson
L.L.Erne (Humphrey’s I.) Combination Permanent Battery LWG waders 12.76 0.83 Brad Robson
L.L.Erne (Lusty More) Combination Permanent Battery LWG waders 17 2 Brad Robson
L.L.Erne (White North) Combination Permanent Battery LWG waders 7.8 1.7 Brad Robson
Malltraeth (Tai'r Gors) Combination Permanent Mains LWG waders 16ha 1.8 Ian Hawkins
Malltraeth (Tai Hirion) Combination Permanent Battery LWG waders 13 ha 1.7 Ian Hawkins
Marshside Combination Permanent
LWG waders
Tony Baker
Mersehead Combination Permanent Mains LWG waders 32.11 3.14 Colin Bartholomew
Middleton Lakes Combination Permanent Battery LWG waders, avocet
21.8 2 Kate Thorpe
Minsmere (Scrape) Combination Permanent Mains Terns, avocet 22 2 Annette Rayner
Minsmere (acid grassland) Strand and netting
Temporary Battery
stone curlew
Mel Kemp
Morfa Dinlle Combination Permanent Battery Lapwing 26 2.2 Ian Sims
Nene Washes Strand Temporary Battery LWG waders Tommy Pringle
Newton Marsh Combination Permanent Battery LWG waders
Tony Baker
Northward Hill A Combination Permanent Battery LWG waders 34 2.9 Julian Nash
Northward Hill B Combination Permanent Battery LWG waders 28 2.3 Julian Nash
Old Hall Marshes Combination Permanent Mains LWG waders 23 2 Kieren Alexander
Otmoor Combination Permanent Mains LWG waders 44 2.8 David Wilding
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Ouse Washes (Pilot Project) Strand Semi-permanent Mains LWG waders 44 (2 blocks) 4.1km Mike Burdekin
Ouse Washes (Pilot Project) Combination Permanent Mains LWG waders
7.2 Mike Burdekin
Ouse Washes (Byall Fen) Combination Permanent Battery? LWG waders Mike Burdekin
Pagham Harbour Strand Temporary
Terns
Stephen Webster
Portmore Lough Combination Permanent Mains LWG waders 60 7 Donnell Black
Pulborough Strand Temporary Battery LWG waders 10 1.2
Rainham (Aveley) Combination Permanent Mains LWG waders
Andrew Gouldstone
Rainham (Wennington) Combination Permanent Mains LWG waders
Andrew Gouldstone
Saltholme Combination Permanent Mains LWG waders 27.4ha 2.155km Dave Braithwaite
Shorne Combination Permanent Mains LWG waders 72 5 Julian Nash
Strathbeg Barrier Permanent
Terns 0.5 0.25 Richard Humpidge
Titchwell Barrier Permanent Avocets, gulls Lizzie Bruce
Valley Wetlands Combination & electric
Semi-permanent Battery LWG waders 22 1.38 (comb) 0.67 (elec)
Ian Sims
Wallasea Barrier Permanent
LWG waders, avocet
? ? Rachel Fancy
West Sedgemoor Strand Semi-permanent Battery LWG waders 30 2.2km Harry Paget-Wilkes
Ynys-Hir Strand / Combination
Semi-permanent Mains LWG waders 31.21 2.5 (1.5km strand, 1km
combination)
David Anning
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APPENDIX 6. UK case studies of barrier fences
Fences in perimeter ditches
Elmley NNR
At Elmley NNR, a 6km barrier fence has been installed at the inner edge of a perimeter ditch within a
water-filled perimeter ditch around c.300ha of wet grassland to protect breeding waders from fox
predation (Fig. 1).
Fig.1 Barrier fence at the edge of a perimeter ditch around a 300ha block of wet grassland at
Elmley NNR in Kent
The ditch is considered wide enough for foxes not to be able to jump the fence from the outer bank.
The fence is angled outwards and comprises c.1.1m of wire mesh netting loosely supported by
wooden posts at c.3m intervals. There is a single strand of barbed wire above the mesh fence. This
could be supplemented or replaced with an electrified wire strand. This type of fence is cheaper to
install and maintain than an electric or combination fence but its potential lifespan and effectiveness
is unknown.
Wallasea barrier fence (Rachel Fancy 5 Dec. 2016) In 2016, a barrier fence was installed in a specially excavated perimeter ditch around 80ha of saline
lagoon, brackish marsh and wet grassland at Wallasea Island. The total length of the 140cm high
fence is 4187m. It is made of Tornado 50mm mesh high tensile wire (R15/140/5) with a strand of
barbed wire on the top to make the total height of the fencing 145cm. The 50mm mesh size will
exclude even fox cubs (80mm would probably have been sufficient to exclude all foxes). The barbed
wire is also high tensile to conform to the specification of the rest of the fence. The fence should
protrude 30cm above top water level with the barbed wire 5cm above that.
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The fence is supported on round timber posts (7 feet long, 4 inches diameter) about 4m apart with
strainer posts (10’x6-8”) and struts (7’x4-5”) at major changes in direction. At internal corners, box
strainers were specified to prevent the post falling in under the strain of the wire and pushing the
ditch bank out.
The wire fencing was stapled to the posts down to the water level that pertained when the fence
was installed (c.25cm below top water level). If necessary the water level will be lowered at the end
of the breeding season and the fence stapled lower down the posts.
Fig. 2. Barrier fence installed in a perimeter ditch at Wallasea (top left before the ditch was filled, top right the fence at top water level)
One section of the fence had to exit the perimeter ditch to go round a major sluice. To make the
fence less obtrusive and to enable visitors to naturally look over it, the design of this section was
based on the lower of the two barrier fences in Fig. 5, p.28 and has a full semi-circular, rather than
angled overhang at the top to prevent foxes from climbing this relatively low (115cm plus overhang)
section of fence.
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Fig. 3. The barrier fence around the sluice at Wallasea. Note the extra protection to the corner post.
Cost The total cost of the barrier fence in the ditch (including the extra cost of long reach for berm, the
extra-long strainers etc.) was £67735 (£16.17 per m). At £12000 the fencing around the sluice was
very expensive because it had to cross three ditches, included a gate (Fig. 4 ) and was fitted with the
semi-circular top.
Problems encountered up to February 2017 1. When the perimeter ditch is frozen foxes can walk across it.
2. A fox managed to jump through the 15cm gap between the gate and the barrier fence (Fig. 4).
This was solved by putting some extra wire to close the gap to <7cm where the fence meets the
gate.
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Fig. 4. A fox jumping through a 15cm gap between the gate and the barrier fence at Wallasea. Note that the floppy top butts right up against the other end of the gate with no gap.
Barrier fence in the water between the ‘mainland’ and the breeding island
Hodbarrow Tern Island Anti Predator Fence The requirement was a low maintenance anti-predator fence that would protect terns breeding on a
1.5 ha island in a freshwater lagoon from predation by foxes. The site is not permanently wardened
and has a moderate threat of vandalism/unauthorised access. This precluded the use of high
maintenance electric fencing requiring the use of batteries etc.
The fence was designed, manufactured and installed by Contract Fencing Ltd, Unit 16, Station Yard
Business Park, Station Road, Wigton, Cumbria, CA7 9BA. The fence was adapted from the standard
security fencing, which the company install around schools, businesses etc.
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The panels are semi-rigid coated steel wire 1.8m high by 2.4m long attached to 60mm square hollow
section steel posts. The panels are bolted onto the uprights via a clamp into threaded aluminium
inserts (see above). Both panels and uprights are fully galvanised and polycoated.
The uprights were modified by welding a 600 x 600 mm 3mm steel plate to the base. When the
uprights were placed in the water, the steel plate either settled into the sediment or occasionally
needed to be weighed down with a concrete block. The installation of the 400m long fence was
undertaken by a team of four and took approximately 3 days.
The wire panels can be bolted onto the uprights at any height, allowing for variation in water
heights. The panels were set approximately 0.6 m below the water surface (almost to the lagoon
bottom) and 1.2 meters above the water surface. One section was left unbolted and hung on pegs
welded to the uprights to allow the panel to be removed for access. This can be chained and
padlocked to prevent unauthorised access.
The 400m fence was installed in a zig-zag pattern to increase stability against wind and wave action.
It is possible that the internal corners on the fence might enable a determined fox to climb the
fence. However, it would be possible to retrofit a ‘floppy top’ of overhanging wire mesh to the top
of the fence, at least at the internal corners, if attempts to climb the panels by foxes are detected.
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Fig. 5. The installed fence protecting the tern island to the right from the mainland to the left.
Costs
At 2016 prices, the cost of the fence was £65.20 per metre plus VAT (supplied and fitted) or £44.15
per metre plus VAT (supplied only). The 400m fence at Hodbarrow cost £26080 installed.
Effectiveness
The effectiveness of the fence was monitored by use of a thermal imager, trail cameras and scat
transects throughout the breeding season. There were several night time sightings of a fox
attempting (unsuccessfully) to get round the fence by swimming up and down it before returning to
the mainland. Up until mid May 2016, the fence was successful with the hatching of lapwing chicks
and the initial settling of 12 pairs of little terns, along with ringed plover, oystercather and eider.
Contact: Dave Blackledge, Campfield Marsh. [email protected] Tel. 07753776393.
Rye Harbour In 1999, a 40m linear water fence was installed between the shore of a gravel pit and a large island
at its closest point (15m) and this was successful in preventing access by foxes and badgers to the
gulls and terns breeding on the island. The 10cm hexagonal mesh wire fencing was 90cm tall and
supported on 1.2m untreated wooden posts about 2m apart. The mesh was fixed on the outside of
posts, stapled to the top and at the water line, with 20cm of mesh above the water level expected at
the start of breeding season. Similar fences were installed around another two islands (see below).
Lower Lough Erne Fences were installed on two islands in January- February 2012 specifically to limit the area available
to badgers resident on the islands, with the remaining area left available for waders to breed. Each
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fence crossed the island with the two ends in water (4x12ft gates covered in galvanised 1cm sq
welded mesh with one live strand on top of first 2 gates).
On Rosscor Island (5.96ha) there was a single badger which remained within the fenced area until it
died of natural causes 2 years later. No ground-nesting birds attempted to nest within the fenced
area and breeding wader numbers increased on the rest of the island.
On Muckinish Island (7.01ha) there was a sett including six badgers. On one occasion, one of the
badgers swam around the end of the fence. The gate in the predator fence was opened and trail
cameras were used to monitor what happened. When the badger crossed back into the “badger
area” the gate was closed but it soon swam around again. This time trail camera images showed
that although the other badgers would leave their area via the gate to feed and then return to their
sett, the animal which had swam out would return to the threshold of the gate and not cross it.
Again the number of pairs of breeding waders increased immediately after the fence was installed.
In addition to the installation of the fences, scrub management in winter 2011/12 removed 1.2ha of
alder, ash, hawthorn and blackthorn from each of the two islands.
The graphs below show the combined number of curlew, lapwing, redshank, dunlin, common
sandpiper and oystercatcher pairs. Wader productivity generally cannot be monitored accurately on
the islands. However, on these two islands the proportion of curlew pairs hatching young has
increased since the fences were installed and the presence of alarm-calling adult redshank, lapwing
and oystercatcher suggests successful nesting by these species as well.
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In February 2016, a further fence was installed, to stop predators crossing a drainage ditch
separating the mainland from Humphrey’s Island. The other side of the island is protected by the
fast-flowing River Erne. Again the two ends of the fence are in water (2x 12ft gates covered in
galvanised 1cm square welded mesh with one live strand on top). The main fence comprises
1220mm Tornado horse netting. Attached to the fence, from the top to c100mm below ground (wet
peat/clay) is hot-dipped galvanised 30mm hexagonal mesh rabbit wire. Attached to the bottom of
the horse fencing is a 75cm apron of 1 inch galvanised square weld mesh, turned outwards towards
the drain, pinned at least twice per metre length of the fence and buried below the ground surface.
Not fencing the whole of the site saved a considerable amount of money and so far evidence from
trail cameras show that the fence is working. Badgers and foxes are seen frequently outside the
fence but to date no badger has managed to access the island since the fence was installed. One fox
has been shot but this was outside the fence. Humphrey’s Island is an important site for breeding
snipe. Curlew bred there in 2015 before the fence was installed but were not successful.
Barrier fences around islands (Rye Harbour) Since 1970 Rye Harbour Nature Reserve in East Sussex has managed for nesting seabirds (mainly
black-headed gulls and common terns) on the eight islands within the saline lagoon known as
Ternery Pool B. Yates pers comm.). From 1978 the whole of Ternery Pool was surrounded by multi-
stranded, low cost electric fencing aimed at reducing predation by foxes and badges. The fence
became less effective as fox and badger numbers increased from the mid 1980’s and in response a
much improved fence design was installed around the pool in 2003. In spite of a range of measures
being employed, including predator control, regular predation of nests on the islands through the
1990s resulted in a decline in seabird numbers.
In August 1999 (when water levels were at their lowest), simple barrier fences were installed in the
water around the two islands (60m2 and 75m2) that were closest (12m and 15m) to the lagoon shore
(Fig. 6). These islands were being visited regularly by foxes and/or badgers resulting in the loss of
most or all nests of the black-headed gull sub-colony. The wire fencing was 90cm tall with 10cm
hexagonal mesh supported on 1.2m untreated wooden posts about 2m apart driven into the island
where the water depth allowed working with thigh waders. The mesh was fixed on the outside of
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posts, stapled to the top and at the water line, with 20cm of mesh above the water level expected at
the start of breeding season i.e. the fence would be submerged by higher winter water levels.
Fig 6. The two fenced islands at Ternery Pool in May 2004.
In the first year after fence installation, no seabirds nested on the islands, but a pair of
oystercatchers was successful. For the next 10 years, black-headed gulls and some common terns
nested successfully with no fox or badger predation, although there was occasional predation on
other unfenced islands of Ternery Pool during this period. For the years 2005-2011, the combined
annual average number of birds nesting on the two fenced islands was 236 pairs of black-headed
gulls 236 pairs and 10 pairs of common tern.
In 2012, the water level of Ternery Pool was raised by 50cm as a result of a nearby saltmarsh re-
creation project and the two islands and their fences became submerged. The level of the islands
was raised, but not the fences and in each of the following 3 years there was significant predation by
a fox and/or badger on one of these two islands.
Following the success of the initial two fences, a further three islands have since been fenced on
other saline lagoons achieving a similar 100% exclusion of foxes and badgers, resulting in increased
nesting success of other species including avocet, redshank, lapwing and little ringed plover. To save
money, standard sheep netting was used for this design, but installed upside down with the smaller
mesh at the top. The same fence material was used in a ditch to prevent foxes and badgers crossing
and also for keeping dogs away from sheep.
Of all the fence designs employed at Rye Harbour, barrier fencing around islands achieves the
greatest effect at low cost, with low maintenance requirements and low impact on the landscape.
Trial of floating anti predator fence at Fen Drayton Lakes (Tim Fisher) NB. This design and deployment is at the trial stage at the time of writing (February 2017). As such,
there are likely to be adjustments to the design and the fence is not yet proven to be effective (Tim
Fisher).
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The purpose of the floating fence is to exclude foxes and badgers from accessing an island close to
the shore in Moore Lake where avocets and lapwing have previously attempted to breed. Foxes
have been known to access the island in the past. Fen Drayton is on a floodplain so the potential
water level range is about 2m. Therefore, it seemed that a floating fence might be a more
appropriate, and possible cheaper solution, than a barrier fence.
The fence and booms The fence is about 150m long and will mostly be about 5m from the island shoreline (the fence will
be further way in places where the water depth is too shallow at 5m from shore line).
The floating booms comprise sections of buoyant polyethylene foam sheet rolled and contained in
UV resistant woven polypropylene. The barrier fence is formed by 6ftx3ft (1830x910mm) galvanised
steel weld mesh wire panels with 3” (75mm) 10 gauge square mesh. The fence was built in sections
determined by the length of the flotation sections. Five mesh panels were used per flotation boom,
cable tied to each other in four places.
Each weld mesh section was attached to the boom approximately one third from the bottom by four
cable ties (on either side of mesh for stability).
A heavy (pre-used) chain is attached to the bottom of the weld mesh with cable ties to act as ballast
to keep fence vertical.
Tethering The fence will be tethered to scaffold poles driven vertically into the substrate (Fig. X). A floating
rope the same length of the fence was used to make sure that the poles were located in the correct
position.
Because the potential water level range is approximately 2m, a system using a small weight to keep
the slack out of the tethering rope and the fence close to the intended position will be deployed as
below. It is hoped that this will allow the fence to move up and down with the water level without
drifting too close or too far from the island.
The tethering system is also designed to allow the fence to function properly regardless of which
side of the post it is, as it is possible that this will change as a result of a flood.
Used chain as ‘ballast’ to help keep
fence upright
Weld mesh panels
Flotation sections
Cable/zip ties
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Fig. 7. Scaffold poles in place ready for tethering. The top tether running rings are yet to be fitted.
‘Usual’ water level
Max water level
Min water level
Small weight
Thin rope
tethering loop
Tethering line
Ring for tether to
run through
Ring clip
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Fig. 8. Sections of fence assembled ready for deployment.
Fig. 9. The installed floating fence.
Potential issues Wader chicks hatching from nests on the island might not be able to leave until they fledge.
Previously, oystercatchers nesting on the island have moved their chicks to the mainland shore. To
enable swimming chicks to leave, some short float sections have been removed allowing chicks to
pass through the fence without having to first clamber onto the floats.
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Cost The approximate cost of materials is about £21 per metre of finished fence. Note that several items
had been used previously elsewhere on site (including the wire mesh panels) so some of the costs
below are estimated.
Item Cost (£)
Steel weld mesh panels 1230
Flotation booms 1500
Pre-used chain 225
Cable ties (estimated) 40
Scaffold poles & fixings 158
Rope for fixing (estimate) 30
Rope fixing clips 20
Approximate total cost 3203
Barrier fences on land
Upton Warren Nature Reserve In 2002, a barrier fence was installed around the Flashes section (c.12ha) of Upton Warren Nature
Reserve (managed by Worcestershire Wildlife Trust) (Fig. 10). The Flashes comprise saline pools and
islands managed primarily for breeding waders (little ringed plover, lapwing and redshank). The
effectiveness of the fence is unknown, but avocets nested for the first time in 2003 and have
continued to do so ever since.
Fig. 10. Barrier fence surrounding the Flashes at Upton Warren Nature Reserve
Barrier fence against hedgehogs A vertical barrier of taut chicken-netting (30mm mesh, 0·45m high) was successful at excluding
hedgehogs from 20ha of damp machair grassland on South Uist (Jackson 2001). The fence was
supported by high-tensile wires strung from wooden straining posts 100m apart with smaller posts
at 5m intervals between and sealed to the ground by a 30cm apron on the ground surface out from
the fence and secured every 20cm with U-shaped wire pegs. The fence also had an electrified
polywire offset 80mm from the upper high-tensile wire on the outer side powered by a 12v car
battery every 1000m, but there was no evidence that this was needed to prevent hedgehogs
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climbing over, although it was effective at stopping damage by livestock. Nevertheless, for the
relatively small additional cost, an electric top-wire was considered probably to be a worthwhile
deterrent to prevent hedgehogs climbing over the fence.
A second fence on much drier ground suffered from a high re-entry rate of radio tagged hedgehogs
because rabbits dug under the fence and the holes provided easy access routes for hedgehogs. The
fence was made from 1m wide galvanized chicken-netting attached to the lower 0.5m of an existing
stock fence (on the outside) and continuing at right angles outwards into a 0.4m wide furrow. This
was then back-filled so that the skirt of netting was buried to a depth of about 0.2m
Small-mesh fences limit movements of non-target species, because they are impassable e.g. for
ducklings and wader chicks. These potential negative side effects should be minimised by careful
choice of fence-lines, making exclosures relatively large and using the largest mesh size consistent
with excluding hedgehogs so that smaller animals can pass through.
Fig. 11. Barrier fencing to exclude hedgehogs on South Uist.
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Barrier fencing around Montagu’s harrier nests (J. Scott). After suffering increasing predation losses of Montagu’s harrier nests in oil seed rape fields, RSPB (J.
Scott and M. Thomas) decided before the start of the 2008 season that any nests in oil seed rape
would be fenced after hatching (females are much more likely to desert at the egg stage).
In the first couple of seasons, each nest was surrounded by 12-13m (4m diameter) of 1.2m high
chicken wire fencing. Eight equally spaced steel rods were woven through the mesh and knocked
into the ground with a lump hammer. Tent pegs secured the netting at ground level. More recently
wire netting has been replaced by plastic mesh netting, which is easier to handle. Nests are only
fenced once the young have hatched; adult behaviour indicates when this has happened.
The Dutch employ even smaller enclosures to protect Montagu’s harrier nests than those in Eastern
England (Fig. 12 ), ostensibly to reduce costs. In recent years all nests in the Netherlands (about 50
annually) have been fenced irrespective of crop type and achieve a c.95% success rate in fledging
chicks. Following on from this experience, all Montagu’s harrier nests in Eastern England have been
fenced since 2015.
In Eastern England, one or more nests have been fenced every year since 2008 and so far all have
fledged young, except for one nest in 2015. (The suspicion is that the single chick in this nest
probably died from lack of food or disease rather than predation. The female, breeding for the first
time, was the third female of a male with two other nests and little prey was seen being delivered to
this nest.)
Fig. 12. Barrier fencing enclosing Montagu’s harrier nests in The Netherlands.
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APPENDIX 7. UK case studies of combination fences
Rye Harbour A 6.9km combination fence, enclosing 64ha (split into three separate sections) was first installed at
Rye Harbour Nature Reserve in 2003. The fences protect important shingle habitat, breeding tern
colonies and nesting ringed plover, redshank and lapwing. Their purpose is to keep out foxes,
badgers, dogs and people.
The bottom of the fence runs flush to the ground and has no buried section or apron because this
would have caused too much damage to the shingle (Fig. 1). This means that 1220mm Tornado
fencing could be used for the main fence, with 2 electrified wires above to bring the overall fence
height to 1.5m.
As the shingle vegetation is low and sparse, the fence design could incorporate a low electrified
bottom wire to train animals to avoid the fence, lessening the risk of breaches. This is 10cm off the
ground and offset from the fence by 20cm. The vegetation beneath the wire is sprayed once per
year in late April with glyphosphate to minimise power loss through vegetation touching the wire.
Even so, without an apron or buried section of fence, some animals are able to dig underneath the
fence. To counter this, the barrier portion of the fence is checked weekly for damage e.g. holes dug
beneath it.
The fence is supported by 3” diameter posts every 3m, and larger corner posts (6” diameter). The
design of the strainer posts had to be adapted, because the posts cannot be buried deeply (see Fig.
2). Some parts of the fence are prone to flooding. When this occurs the affected lengths of fence
can be isolated from the electric circuit by cut out switches. Daily checks of the power supply are
made during the breeding season. If there is a problem, then sections of the fence can be isolated
using the switches, making it easier to locate a problem with a voltmeter.
Fig. 1. Combination fence across shingle at Rye Harbour. Note the moderate visual impact and
undulations in the landscape.
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Fig. 2. Barrier fence at Rye Harbour showing the switch (yellow) to isolate fence sections, the
straining post design using horizontal posts and the low offset electrified wire.
Although the bottom electrified wire is only 10cm above the ground surface, no dead or injured
wader chicks have been found to date. The fence has proved effective against badgers and only one
(a cub) has been found inside. However, 7 or 8 foxes have been found inside the fence since it was
installed; most are thought to have burrowed beneath the fence.
Rabbits are able to move through the fence freely, but adult hares cannot. The predator-free
environment inside has meant that rabbit numbers are a problem, as they eat the vegetation,
including rare plants. Numbers are controlled by shooting at night.
To stop crows perching on them all posts have a 6” screwfix screw on top (Fig. 3); the larger strainers
need four screws.
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Fig. 3. Six inch screws on posts to prevent avian predators from perching.
Visitors Many people come to the reserve to walk their dogs and there are complaints about the electric
fence. An extra fence has been added to some sections to make a double fence line between the
footpath and the electric fence to stop people/dogs coming up to electrified fence. Even a low
single wire will keep people from straying up to the electric fence. In addition, there are many
warning signs along the fence and a visitor information board explaining why it was installed (Fig. 4).
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Fig. 4. Visitor information board about the combination fence at Rye Harbour.
The evolution of fencing arrangements It is always worth letting the fence into ground including straight down with no apron and this has
been done in some less sensitive areas i.e. this is better than just an apron or skirt on the surface. In
other places a horizontal 30cm netting apron on the ground surface butted against the outside of
the fence has been installed to prevent badgers (and rabbits?) from digging under but only where
vegetation grows through to hold it in place. Where the edge of the apron curls and becomes proud
of the substrate (e.g. in bare areas), badgers will dig underneath.
To improve the performance of the fence against badgers digging beneath it, an additional live wire
has been run along the inside of the fence (i.e. there are live wires 10cm off the ground on both
sides of the fence). The performance was improved further by increasing the power of the energiser
to 56 joules.
The total length of fencing has been increased to 15km at a total cost of £210K.
Rainham Marsh A combination fence was installed around the Aveley Marshes section of the reserve in 2010.
Following improvements to the wet grassland habitat at Wennington Marsh in 2014 and 2015, a
second fence 4.2km long was installed in 2016. The design incorporated several improvements over
the original fence: it is 20cm taller, the Tornado fencing has a smaller mesh, there is an additional
live wire above the barrier fence and a 40cm apron is pegged to the ground surface.
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However, the main attribute of the new fence is the incredible attention to detail paid to its design
and construction. It has yet to be penetrated by a fox or badger and lapwing nest success and
productivity was very high in 2017. The fence took two fence contractor employees living on site 16
weeks to install it (and another 2km of standard stock fencing). It became operational just before
Christmas 2016.
Bespoke solutions were required to cross individual ditches, and the contractors were required to
identify and resolve these at each location. Reserve staff provided regular support and supervision
to ensure the best end product was delivered. Final electrical connections and the gate detail were
undertaken by the reserve, primarily by skilled volunteers.
The major design difference from the Aveley fence was the mesh size of the high tensile wire fencing
used. This was made to a bespoke specification by Tornado Wire, which they now stock as a special
fencing designed for anti-predator fences with a mesh size of 50mm x 100mm for the full height of
the fence (Product: R18/170/5 C5 PREDATOR FENCING). This mesh size should exclude otters (not
currently on site at Rainham). The total height of the wire fence is 170cm. The top 130cm is secured
to the outside of the fence posts. The bottom 40cm has a hinge joint enabling it to be turned
outwards at right angles to form an apron or skirt that lies flat on the ground surface. This avoids a
potential future weakness as a result of the wire itself being bent. The leading edge of the wire
apron is pegged down at intervals (three pegs between each fence post to prevent animals digging
underneath. Once the vegetation has grown through it, the wire mesh is no longer visible (usually
by the end of the first growing season). The Aveley fence had a section trenched in, the apron
option on the Wennington fence was selected to reduce the cost and because of UXO
considerations.
Fig. 5. The bottom 40cm of the 170cm high netting has a hinge joint enabling it to be turned outwards to form an apron on the ground surface. After one growing season this is no longer visible.
The new fence has an additional off set live wire that increases the fence height to 170cm and a live
wire on the inside of the fence to stop stock rubbing against it (Fig. 6).
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Fig. 6. The combination fence design at Wennington Marsh, Rainham showing the arrangement of the netting and wire strands.
Fig. 7. The arrangement of three live and one earth wire at the top of the fence with an additional live wire on the inside. Note that the insulators have orange inserts of hardened plastic to increase their longevity.
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Six wires (five live, one earth) are continued across the top of the metal gates, supported by
insulators attached to vertical metal brackets welded onto the top of the gate. This has kept the
height of the gates greater than the height of the fence. The mesh is welded onto the outside of the
gate structure. The gates cost £300.
To prevent anything digging under the gates, concrete sleepers were let into the ground directly
beneath each gate. The sleepers are hollow in cross section, which reduces the weight and is
installed flush with the ground surface. (The concrete sleepers were salvaged from elsewhere on
site.)
Fig. 8. Note the concrete sleeper beneath the gate, the use of proper connector or line clamps to join the lead-out cable to the high tensile wires and the anchor insulators, which take the strain of the wires and maintain good tension at the beginning or end of the fence.
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Fig. 9. A hinged mesh flap enables access to the gate lock while keeping the gate secure.
To prevent the wires slumping and shorting out, they are tensioned with corrosion-resistant alloy
wheel tensioners (Fig. 10). These slot onto the wire and then twisted and locked with a 12mm
ratchet handle.
Fig. 10. Galvanised wheel tensioners keep the high tensile wires taut.
As well as box strut strainers, additional strainer posts are not obvious as most are tied back to a
buried anchor (a system known as a dead man or dead man’s stopper), every 100m.
All thicker ‘strainer’ type posts were fitted with ‘postsavers’ (a polythene outer layer with a meltable
bituminous liner) to delay the posts from rotting at the ground line (Fig. 11). The surface of the
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posts was pitted (Agricised) to increase penetration of the preservative. The posts are guaranteed
for 10 years.
Fig.11. Posts were equipped with ‘postsavers’ and pitted (Agricised)to enable better penetration of the preservative.
Fig. 12. The design for the floating section of the Wennington fence.
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One major issue encountered in the project was the need for the fence to cross a section of an EA
Main River. EA would not consent for any permanent fencing through the channel. To overcome
this, a floating section of fence was constructed that was designed to move up and down with the
water level within the channel (Fig. 12). The floating fence is a raft constructed of drainage pipe and
timber, which supports upright posts with the fencing attached and electric fence insulators that
carry the electricity across the water.
The mains powered energiser is held in a brick outbuilding. The fence voltage is checked daily and
instructions for doing this are posted in the reserves office (Fig. 13). As with the original Aveley
fence, regular maintenance checks of the fence will be undertaken throughout the year, with two
highly focussed ones undertaken in Jan and Feb , just prior to the breeding season. Vegetation along
the fence is managed by staff and volunteers using brushcutters and a pedestrian mower. This
ensures maximum voltage during breeding season.
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Fig. 13. The instructions for checking the fence voltage (kV) posted in the Rainham office
Great Bells Farm, Kent Two combination fences were installed at Great Bells Farm in autumn. 2015. The two battery powered fences will be operated all year round, with the gates shut and electric levels maintained and regularly checked. The location of the two combination fences is shown below (Fig. 14).
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Fig. 14. The location of the two combination fences at Great Bells Farm
The 4.3km fence protects 110ha of wet grassland. Supplementary groundworks and fencing cost
£6K and the anti-predator fence itself £58K installed. The specification provided to the contractor is
shown below. The other fence (Peninsula) was 2.34km long and was to the same specification.
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LWG Electric Fence 4330m
Feature/item Description Map/Drawing ref
Livestock netting
(LWG-EF)
• XHT17-190-7.5 mesh: o 1.6m above ground height o 0.30m buried below ground
GBF Electric Fence Drawing
1 20150122
Wooden posts
(LWG-EF)
• Quality, rot resistant - class 4 pressure treated softwood:
o 2.4 metre full round 100mm softwood posts at 3 metre maximum intervals.
o Full round 150mm 3 metre strainer posts where needed at changes of direction and at 100 metre maximum intervals
GBF Electric Fence Drawing
1 20150122
Electric wires
(LWG-EF)
• 4 strands of electric wire in off-set isolators: o Live strand (1) inside fence 1m above
ground and off-set by 200mm o Live strand (2) outside fence 1.5m
above ground and off-set by 100mm o Earth/neutral strand (1) outside
fence 1.6m above ground and off-set by 200mm
o Live strand (3) along the top of the fence posts and off-set by 100mm
GBF Electric Fence Drawing
1 20150122
153
Positioning
(LWG-EF)
• 8m in-field from Main River ditch edge to maintain maintenance access for RSPB & IDB outside the fence
• 5m in-field from Ordinary Watercourse ditch edge to maintain maintenance access for RSPB & IDB outside the fence
GBF Electric Fence Map 1
20150122
Electric fence gates
(LWG-G1 to G7)
• 7new gates within the perimeter of the fence: o 3.6m x 1.8m Deer Gate o 2x Electric Spring Gate wires per
fence; 1 for live strand 2 and 1 for earth/neutral strand 1
o Wooden sleepers dug into the ground at the base of the gates to prevent predators digging under the gates
GBF Electric Fence Map 1
20150122
New culverted
crossings
(LWG-C1 to LWG-
C4)
• 4 new culverts (per culvert): o Site-won clay construction (adjacent
borrow pit) o Topsoil removed to provide secure
water retaining key between existing and new materials
o 4m crest width o 2.05m AOD crest height finished
with: o 150mm crushed concrete dressing
over a vegetation suppressing ‘Terram’ layer to bring completed height to 2.2m AOD. Area to cover is 12m x 4m = 7.2m3 of crushed concrete
o 45o batters where required o 1x 300mm Solid Twinwall pipe
through culvert
GBF Electric Fence Map 1
20150122
GBF Electric Fence Drawing
2 20150122
New metal field
gates and wing sets
• 4 new 12’ internal metal field gates and wooden wing sets either side of gates to maintain livestock and grazing control for each of the new culverts LWG-C1 to LWG-C4
GBF Electric Fence Map 1
20150122
GBF Electric Fence Drawing
2 20150122
Power installation
protection fence
• 1 new 4m x 4m fence and integral field gate around power installation to protect from livestock damage
o 2 sides (8m) standard post and 4-rail (half-round) protection fence
o 1x 12’ metal field gate on appropriate third side (TBC)
o Note that the fourth side will be the electric fence itself
o Location TBC
-
Welfare facilities • Welfare facilities are present on site and will be available to the contractor and their staff for use during the construction of the fence.
GBF Electric Fence Map 1
20150122
154
Winter/wet
working
contingency
• The work is scheduled to be undertaken between August and November inclusive – the driest time of the year. However, if the project experiences delays caused by RSPB and/or significant wet weather during this period and has to be undertaken during the winter/significant wet weather, a winter/wet working contingency sum should be supplied as a separate item to accommodate winter/wet ground conditions. The sum should include elements such as tracked dumpers and works to remediate soil damage such as significant rutting etc.
• This sum will only be applicable if the above scenario becomes reality.
• This sum is not applicable to delays in delivery caused by the contractor, resulting in construction over-running into winter ground conditions and any damage caused to ground condition and infrastructure by an over-run. All costs of remediation in this scenario will be the contractor’s responsibility.
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APPENDIX 8. Detecting the presence of foxes and badgers inside an anti-
predator fence.
Tracking plots Tracking plots should be placed close to the boundary of the fence. Plots can be created by
removing 1m2 of turf and replacing it with compacted sand to a depth of c.5cm, and burying c.25g of
bait in the centre of the plot at c.2cm depth. Low-protein Pedigree Chappie©dog food (Pedigree
Petfoods, Melton Mowbray, UK) is a short-range bait that will attract foxes over a range of c.3–5m.
Soil should then be sieved over the entire track plot and watered to prevent desiccation, which can
impair the detection of predator footprints.
Thermal imagers Foxes quickly become lamp shy and can be hard to pick up by traditional lamping methods.
Therefore, it is a good idea for sites with anti-predator fences to invest in a thermal imager as a way
of checking for the presence of foxes and badgers at night as part of the routine monitoring
program. A £3k thermal imager is cheap in comparison with the capital cost of a predator fence that
fails.
Thermal imagers are a completely passive infrared sighting system that picks up the infrared heat
from a source and relays this to an OLED screen i.e. the thermal imager will detect the infrared heat
source and transmit it to the eye as a viewed image. They allow users to identify the heat signatures
of objects day or night and in rain.
Handheld thermal imagers RSPB staff have some experience in the use of thermal imagers to locate and shoot foxes. The Pulsar
is rated very highly in the fox shooting world and Minsmere and Old Hall have bought Quantum
HD50S thermal imagers and found them to be suitable hand-held devices for finding foxes to shoot.
The Pulsar Quantum HD50S thermal imagers were purchased from Scott Country.
http://www.scottcountry.co.uk/products-Pulsar-Quantum-HD50S-Thermal-Imager-5647.htm
Scott Country run a 7 day trial scheme whereby they will send out a unit free of charge and then you
either keep and pay for it, or send it back (undamaged!) for a £25 charge.
The Pulsar Quantum HD50S has a quick start up time (< 5 seconds) and an optical 2.8x magnification
(plus a 2x digital zoom) to provide a detailed image at ranges of up 1250m via a 640x480 high
resolution OLED display that provides a high quality image across the whole field of view with no
tunnel effect. It has three Viewing modes: City (enhanced contrast), Forest (low contrast),
Identification (improved rendering of details of ‘hot objects'). The HD50S can be used in inclement
weather and can ‘see’ through fog, smoke, or obstacles such as long grass and foliage. It weighs
0.43Kg and is powered by 4 AA batteries giving a run time of up to 5 hours. To extend run times, a
connection is provided for an external battery pack EPS3.
The Pulsar-Quantum HD50S has recently been replaced by the Pulsar-Quantum XD50S Hand-Held-
Full-Colour-Thermal-Imager costing £2900. The new model has a 1250m detection range and the
benefit of a colour palette (which might increase definition for improved identification). It also has
an improved optical and digital zoom and a built in rangefinder,
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Scott Country also sell the range of Guide IR518 thermal imagers, which have a similar specification
and price to the Pulsar Quantums.
http://www.scottcountry.co.uk/products-Guide-Infrared-IR518-Thermal-Imagers-4991.htm
In 206, Eastern Moors bought one through TBF systems (not Scott country). It came recommended
as the best thermal imager available to civilians. Medium-sized mammals (foxes/badgers) can be
identified positively at ranges up to 200m (and detected further away).
Drawbacks of thermal imagers
The depth of field is shallow and needs frequent re-focusing. If using at night from a vehicle or a
room, the heaters should be switched off i.e. keep the room and vehicle cold or step outside.
Thermal imagers cannot be used through glass and they cannot ‘see’ into water. On mosquito
infested evenings it is better to set-up the thermal imager on the roof of the vehicle and sit inside
watching on a separate screen.
Contrary to what the suppliers say, mist/fog and blizzard conditions are often the ‘Achilles’ heel’ of
thermal imagers. In fog animals can be no easier to detect than with the visible spectrum. In
blizzard conditions the TI screen tends to grey out (e.g. making deer that can be seen at 300m
invisible to the TI).
Trail Cameras Trail cameras are remote camera traps triggered by an infra-red motion sensor to take images
during daytime (colour or black and white) or in the dark (black and white via infra-red). Images are
recorded onto an SD memory card which can be viewed on a computer. Most trail cameras record
additional information, such as time and date.
Positioning
Cameras should be attached to the wing posts of gateways in the fence or to stakes within two
metres of a gateway or internal boundary of the fence, with the camera pointed along the fence or
gate and angled slightly into the field. The PIR sensor should be c.0.6 m above ground level and the
horizon about midway up the picture. The camera must not point into the ground or into objects
close to the camera that might bounce light back (causing massive overexposure). It is important to
site the camera carefully to reduce the chance of moving vegetation triggering the motion sensor.
Exposed situations should be avoided as strong winds often cause false positive images because the
camera detects changes in temperature due to either moving vegetation or movement of the
camera and/or the post on which it is mounted on (either of which could have the same effect).
The efficiency of camera traps in detecting foxes can be improved (i.e. the chances of detecting the
presence of a fox increased) if they are used in conjunction with bait pits to attract foxes close to the
camera.
Checking
The cameras should be checked frequently (every 2-3 days) to ensure the batteries and memory
card are still operating and to replace them if needed.
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Potential drawbacks
The cameras can be easily disturbed or damaged by cattle if the fenced area is being grazed,
reducing the number of available locations for set up.
‘False absences’ can arise if the PIR does not detect the fox or badger e.g. if it passes too quickly or
too closely to the camera trap to trigger or if there is insufficient temperature difference between
the animal and the background. A comparison with cameras taking time-lapse images revealed a
surprisingly high proportion of false negative responses i.e. false absences.
Which trail camera?
The performance, including sensitivity and response (trigger) time, varies with the make of camera (see
below). The speed of first image capture (trigger speed) and the interval to the second picture (the
recovery time) is critical and different makes and models can be compared at
http://www.trailcampro.com/triggerspeedshowdown.aspx .
Cheaper models may ostensibly offer similar features to high-end models for less capital outlay, but
may lack the reliability and performance of more expensive ‘professional’ models that require a
more substantial initial investment, but which may prove more cost-effective in the long-term.
Most cameras utilise infra-red LEDs which are visible when the camera is triggered. Even 'low glow'
models, although not bright, can still be seen. This can be overcome by so-called covert or ‘no glow’
camera models that utilise ‘black flash’ but, on the downside, this reduces the flash range.
The two most popular camera models in use by RSPB staff are various versions of the Bushnell 8MP
Trophy Cam and the more expensive ‘professional’ Reconyx Hyperfire PC800 that costs over £400.
The main attributes of the Bushnell and the Reconyx Hyperfire HC500 (cheaper and more readily
available in the UK than the PC800) are compared below.
TrailCam Pixels Flash/range Detection
Range1 Battery Shutter lag2 Price
Bushnell 8MP Trophy
Cam 8 MP
LED (32)/45
feet 90 feet AA (8) 0.11 second £144
Reconyx HyperFire
HC500 3.1MP
Low Glow
IR/40-50 feet 50 feet AA (12) 0.22 second £325
1Detection range is an average and varies with ambient temperature. 2 Video trigger speed is much slower (3.2 seconds for the Bushnell)
Bushnell 8MP Trophy Cam Reconyx HyperFire HC500
Pros
Up to 8MP resolution (interpolated)
32-LED flash, with 15m range
0.11 second trigger speed
3.1MP or 1080p resolution
Low Glow Semi-Covert IR Flash
Flash range of 50 feet
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Field Scan time-lapse photography
Full colour resolution day and night
Up to 60 seconds of video with sound
Motion activated day and night PIR sensor
(Passive Infrared)
Sensitivity of PIR sensor is adjustable
Photos stamped with time, date, temp and
moon phase
Weather proof construction
Compact design
Runs on 8 AA batteries
One set of batteries lasts up to 1 year. Note:
Use of video will drastically reduce this.
Mounts with adjustable web belt
Rugged weatherproof case
0.22 second trigger delay
Fast picture Recovery Time: 0.9 secs
Takes up to 32GB SD card
Photos stamped with time, date, temp and
moon phase
12 AA batteries
Password protected
Cons
Can be tough to remove batteries.
Slow picture recovery time (3.8 secs).
Night pictures are dark and blurry. Animals
further than 35-40 feet are exceptionally grainy
and small animals are often indistinguishable.
Close-up photos are overexposed and appear
blurry (see below)
No video
The Trophy Cam tends to overexpose night images when the subject is close (<4m). However, it
might be worth investing more money and buying the Bushnell Aggressor HD (£189) which produces
much better red glow infrared night pictures. It is also very responsive with a 0.13 second trigger
time and recovery is under 1 second (i.e. it will take one picture every second).
Conclusion
Differences in functions and reliability command a difference in price, with ‘professional’ camera
traps (e.g. Reconyx Hyperfire PC800) costing two to three times as much as mid-range units (e.g.
Bushnell Trophy Cam HD 119737). Reconyx are clearly better than Trophy Cams. Build quality and
quality control are superior, giving a slicker and more user-friendly product and the camera comes
with better supporting information. However, the Bushnell Trophy Cams are a good and cheaper
alternative.
Reconyx cameras are distributed in the UK by Perdix Wildlife Supplies
www.perdixwildlifesupplies.co.uk and Digital Wild Cam http://www.digitalwildcams.co.uk/.
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APPENDIX 9. Box Strainers Like many fencing techniques, the use of box strainers was developed in New Zealand. As in a
conventional strainer, the box strainer relies on the principle of the triangulation of forces, but in the
case of the box strainer, the force is taken by the strained wire.
The box strainer is a more complex structure than a conventional strainer, with more to go wrong,
and its use is probably best restricted to situations where a conventional strainer is difficult to build.
Single and double box strainers are widely used for high tensile fencing.
A box strainer is only slightly more expensive than a conventional strainer, because although two
posts are needed, they are of smaller diameter. The box strainer is as strong as a conventional
strainer in firm soil. In weak or very shallow soils the box strainer may perform better than the
conventional strainer. The posts in a box strainer are best driven into the ground. The fitting of the
horizontal stay and the tensioned wire takes longer than fitting a strut. The box strainer is not
suitable for areas where vandalism is a problem, as the whole assembly will fail if the wire is cut.
Where ground conditions are difficult, or very high strains have to be held, a double box strainer can
be constructed. This has over twice the strength of a single box strainer. Although the optimum
depth is 1m (3'), it is possible to construct a double box strainer in only 300mm (1') depth of soil, for
example over bedrock.
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Construction of Box Strainers The two posts should be knocked into the ground the distance apart of the horizontal stay. Then cut
recesses of about 15mm (1/2") near the top of each post and place the stay in position. Drill a hole
through the post into the stay, and then hammer in a 200mm (8") length of 12mm (1/2") mild steel
bar. Repeat at the other end of the stay. Follow the procedure for straining and fixing a retaining
wire as shown here: https://www.youtube.com/watch?v=EAhFpx9lLFQ
Box struts The same principle is employed in the box strut, which is a very useful device for fence corners,
slopes, and for repairing and strengthening posts and strainers. The following diagrams show some
of these uses.