Water shrew survey booklet

Reg Charity No. 221819

NORTHUMBRIA MAMMAL GROUP

Northumberland Wildlife Trust Ltd

Garden House

St Nicholas Park

Gosforth

Newcastle upon Tyne

NE3 3XT

Tel: (0191) 284 6884

Fax: (0191) 284 6794

Email: mail@northwt.org.uk

Web: www.nwt.org.uk Design by: E.Beamsley - ebeamsley@hotmail.com

Northumberland

Compiled by Kevin O’Hara for the Northumbria Mammal

Group, with the support of the Local Heritage Initiative and

Northumberland Wildlife Trust.

Photography by Dr Steve Furness

Compiled by Northumberland Wildlife Trust

Black fur on back and a silver

grey/white underside. Often has

a white patch above the eyes.

Size up to 10cm in length, with a

4–7cm long tail.12–18g in weight.

The water shrew is one of Britain’s least known mammals, and there is concern

that it may be undergoing a decline in numbers and occurrence as a result of

habitat loss, pollution, pesticide use (sheep dips) and predation from non-

native species such as North American mink. Despite a widespread geographical

distribution in Britain, there is little information on its occurrence, habitat

preference and population status. Additionally, there are still large gaps in its

distribution records. One of the reasons for the lack of knowledge about this

mammal, is the difficulty associated with surveying such a small, unobtrusive

animal whose field signs (faecal pellets and tracks) are easily overlooked

amongst dense vegetation.

Water shrews are semi-aquatic insectivores, found most often in habitats

close to fresh water, although they do inhabit beaches at certain times of the

year, where they feed on sandhoppers. Their breeding season is between

April and September and during this time 2-3 litters of young are produced.

Water shrews spend most of their time searching for food as they need to eat

roughly half of their body weight daily. Freshwater invertebrates make up the

largest proportion of their diet, although terrestrial invertebrates such as worms

and beetles, are also consumed. Water shrews favour the vegetated banks

of shallow, unpolluted rivers, streams and still waters.

‘Neomys fodiens’

Status native. Protected under schedule 6 of the Wildlife and Countryside

Act 1981 conservation status unknown, although thought to be a declining

distribution, throughout mainland Britain. Absent from Ireland.

Appearance:

Latin name:

To provide a baseline against which to monitor future changes, to water

shrew populations.

To establish the habitat requirements and preferences of water shrews,

and to examine the potential impact of both habitat, and water quality

changes on water shrew populations.

To gather sufficient records to provide a database for the assessment of

the conservation needs of water shrews, and to produce habitat

management guidelines for these mammals.

This survey will employ an easy-to-use bait tube method to investigate the

current distribution of the water shrew.

Aims of the survey

Typical size of a water shrew

Water shrew

RECOGNITION

BACKGROUND TO THE SURVEY

1 Water shrew survey booklet | 2

Each survey pack contains enough equipment for you to survey two sites

simultaneously. Sites should be situated at least 1km apart and the surveying

methods for different types of site vary.

Rivers, streams, ditches. Choose a 40m stretch of the watercourse, and at 10m

intervals place one bait tube firmly on the ground amongst the bank vegetation.

Ponds, lakes, fens, bogs. Where space permits, place bait tubes at 10m intervals.

If the site is small then place the tubes at approximately equal distances around

the site.

Choosing suitable sites for the survey

To enable us to analyse your data we need you to record the grid reference of your

sites. To do this you will need an ordnance survey map of your area. Pinpoint your

chosen location by eye, and then take a grid reference from your map, please follow

the example below:

GRID REFERENCING YOUR SITE

Record the 2-letter reference code found on the map. The

National Grid divides Britain into 100km squares, each with

its own two letter reference. For this region it will be either NZ,

NT, NU or NY.

Next you need to take the Eastings reading. This is the horizontal

reading off the map. This will give you the first two numbers of the

square your site is in, for example 71 grid line. As we need a 6

figure grid reference we must estimate how many tenths are within

that square, and estimate the location against this figure, thus we

have for example NZ 716. The Eastings reading is, therefore, 716.

The same method needs to be applied to the Northings reading,

If the location lies four tenths north of gridline 44, then the Northings

reading is 444.

The whole grid reference you need to quote is, therefore,

NZ 716444.

There are diagrammatic example on all ordnance survey maps

to assist further.

The bait tube method, designed by Dr Sara Churchfield, encourages water shrews

to visit short lengths of plastic tube by baiting one end with food. Faecal pellets

(scats), deposited in the tube by the shrews and other small rodents, can then be

identified and separated. Scats of water shrews are distinguishable from other

shrew species, as they are the only ones that will contain the remains of aquatic

invertebrate prey.

THE BAIT TUBE METHOD

Bait tube in a ideal locationWater shrew

3 Water shrew survey booklet | 4

The bait tubes are 20cm long (4cm wide), pieces of white plastic waste pipe. To

prevent the bait spilling out of the tube, cover one end with a piece of muslin and

secure it in place with a rubber band. The recommended bait is blowfly pupae.

These are available from fishing tackle shops, where they are known as “casters”,

and are sold by the pint for around £3 (one pint should suffice many tubes). You

will need to locate a supply of this bait, as this cannot easily be provided by The

Northumbria Mammal Group as the casters need to be frozen to prevent them

emerging into adult flies. A small tablespoon full of casters (approx. 20-30) should

be placed in each tube, close to the covered end.

PUTTING TOGETHER THE BAIT TUBES

To determine the types of habitat used most commonly by water shrews it is

important that habitat characteristics are recorded. A number of field forms have

been included in your pack, and more can be photocopied or supplied as required.

You need to fill in a form for each site you visit when you first lay out the bait tubes.

At the top of each form you need to record your name, the site name and grid

reference, the dates you visited the site and the number of bait tubes laid down at

each site. In the boxes lower down the sheet, e.g. habitat type, water depth, choose

just one option within each box by placing a cross in the appropriate circle.

We can only record one option on the database, and we will have to exclude

data from our records if more than one circle per box is crossed. If you are

unsure of the answer, then please record this in the comments box at the bottom

of the form.

RECORDING SITE DETAILS AND HABITAT CHARACTERISTICS

At least 4 tubes should be placed at each site.

Always place tubes in habitats with ready access to water.

Place tubes within 2-3m of the water’s edge; the closer the better. Tubes

placed in bank side vegetation are most likely to be visited by the shrews.

Sites with no vegetation are not recommended.

In bog or fen sites, place bait tubes in dry places, for example: grass

tussocks above water level, to avoid them being flooded during the

survey period.

All bait tubes should be placed high enough above the water level to

prevent flooding.

Bait tubes can be secured with wire hoops if necessary. Place them either

horizontally to the watercourse, or with the entrance facing away from the

water depending on the bank structure and vegetation type on site.

Tubes should be left for 2 weeks. During this time you do not need to visit or

rebait the tubes.

To help in finding the tubes at the end of the 2 week period, tie brightly coloured

string or wool to nearby vegetation or marker sticks. Please remove these

markers after the survey is completed.

After leaving the bait tubes for two weeks the scats can be dried and

collected The tubes can then be rinsed and placed at two more sites for a 2-

week period. This will give us information from a total of four sites.

You can survey more sites if you wish, just repeat the above process.

Bait tube within an ideal locationPlacing bait tubes next to the river bank.

The following factors need to be considered when positioning the bait tubes:

PLACING THE BAIT TUBES AT YOUR CHOSEN SITES

5 Water shrew survey booklet | 6

Bait tubes can be washed out and re-used as often as required. For your local fishing

tackle shop try www.uk-fishing.com and click on “Tackle shops of the UK”, or try

your local Yellow pages under fishing tackle shops. Alternatives for bait include

frozen prawns, flaky fish food, tinned cat food or trout pellets, although all are inferior

to casters.

Collect and dry the bait tubes (put them in a shed or similar for

a couple of days).

Remove the dried tube contents including scats etc into a storage

receptacle, such as an empty film canister (avaliable from

photographic shops) or into a small plastic bag. Lids of film

canisters should be taped securely to prevent them opening

during posting. Scats from all tubes at a single site can be

collected and stored in the same receptacle. However, please

keep scats from different sites separate.

Scats are most easily identified if they are intact rather than

crushed, although it is still possible to make positive identifications

from very small fragments.

Label your samples with your name and site identification details.

If you are confident about distinguishing rodent from shrew scats,

you can sort through your samples and only send us the shrew

scats. If you are not confident about distinguishing between

rodent, and shrew scats don’t worry, just send the whole sample

to us, where we will examine them.

Please remember to include your field forms with the grid

reference, site, habitat data and your name and address. We

cannot include your site in the database, nor identify your scats,

if you do not send us the field form.

COLLECTING THE SCATS AND WHAT TO DO WITH THEM NEXT

HOW TO DISTINGUISH SHREW FROM RODENT SCATSThis can be achieved with the aid of a hand lens. The following guidelines may

assist.

If you are confident at identifying the remains of freshwater invertebrates and therefore,

identifying water shrew scats, then please do so. This will require the use of a binocular

microscope. Some workshops will be run to assist volunteers, who wish to learn to

carry out their own water shrew scat identification. Please see Northumberland Wildlife

Trust website at www.nwt.org.uk or call NWT for details on: (0191) 284 6884.

Brown/black in colour.

Cylindrical and pointed at one end.

3-5mm in length.

Tough and difficult to crush, vole

scats are more rounded, and soft

like putty when fresh.

Fibrous texture when broken apart.

Smooth surface.

Rodent scats:

Black/gray in colour, pale gray

when dry.

Oval with a sharp point at one end.

3-5mm in length.

Easy to crumble.

White or silvery fragments of

their prey visible.

Uneven and irregular surface.

Shrew scats:

9 Water shrew survey booklet | 10

Field studies in the vicinity of water can

be hazardous, especially if there are

steep banks. Where possible it is best

to work in pairs. The Mammal Group

takes no responsibility for personal injury,

incurred by volunteers during the course

of their surveys. Handling of faecal

material from small wild mammals

presents no danger of disease, provided

that reasonable precautions are taken

to minimise any possible risks.

Remember to wash your hands after

collecting the bait tubes and extracting

and sorting the scats from the field sites

- especially before eating or drinking.

Cuts or abrasions on the hands should

be covered by sticking plaster or rubber

gloves.

HEALTH, SAFETY AND CARE OF THE COUNTRYSIDE

Take particular care with these simple

precautions in sites where brown rats

are common, as there may be a risk of

Weil’s disease (leptospirosis). For more

information and free publications call

the health and safety executive on

01787 881165.

Caution: Do not trespass. If you choose

to carry out your survey on private land

that does not belong to you e.g on a

nature reserve or other officially-

protected area, then make sure you

have permission to enter the area and

set your bait tubes. The Mammal Group

takes no responsibility for anyone

caught trespassing without permission.

Please take care with personal safety during the course of your survey...The following summarises the full survey methodology used:

1. Read through this information leaflet.

2. Make your 4 bait tubes.

3. Choose suitable sites to place your tubes.

4. Place your tubes at your chosen sites and leave for two weeks.

5. Record site details and habitat characteristics on the field

forms provided.

6. Collect tubes and store scats (faecal pellets) in envelope provided.

7. Wash the bait tubes and repeat steps four to six at two further

occasions for two weeks.

8. Label scat samples with your name, the site name and the

grid reference.

9. Send scat samples and field forms to Northumberland Wildlife

Trust at the address overleaf.

SURVEY CHECKLIST

11 Water shrew survey booklet | 12

NOTES

Water shrew survey booklet | 1413