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Levels and trends in the population
of Red-throated Diver in Sweden DIVER Workshop, Hamburg, 24-25 November 2016
Mats O.G. Eriksson
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Levels and trends in the population of Red-
throated Diver in Sweden (+ Finland)
1. What is Projekt LOM
2. Population levels and breeding range
3. Ecological differences between Red-throated
Diver and Black-throated Diver on breeding
grounds
4. Trends in population size and breeding
performance
5. Ringing – migration – annual mortality
6. Red-throated Divers and onshore windfarms
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Projekt LOM
http://birdlife.se/sveriges-ornitologiska-
forening/fagelskydd/artprojekt/projekt-lom/
Start in 1994, working gruop linked to the national BirdLife partner since 2015.
More than 500 volunteers have contributed with reports during at least one year since start.
During recent years ca 140 persons have been active in the volunteer network
In addition, check against the national bird reporting database, Artportalen.
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Red-throated Diver (Gavia stellata)
Photo: Leif Strandberg
Trend
World population
North America
100 000 – 300 000 pairs
ca 40 000 pairs
0 / - = Europe, Asia
0 = North America
Europe (excl. Russia) 7 100 – 13 000 pairs 0 / +
Sweden, Finland, Norway 4 100 – 8 400 pairs – 62 % 0 / +
Sweden 1 300 – 1 900 pairs – 16 % + = North and Central Sweden
- = South Sweden
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North and North-central
Sweden (Norrland)
South-central Sweden
(Svealand and Dalsland)
South Sweden
(Sydsvenska Höglandet)
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Photo: Jan Schützer
Photo: Bosse Haglund
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Photo: Jan Andersson
Photo: Mats Eriksson
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Photo: Anna Peman
Photo: Janos Jurka/N
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Photo: Mats Eriksson
Photo: Mats Eriksson
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Photo: Mats Eriksson
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Black-throated Diver / Red-throated Diver
RTD
Breeding lakes Large nutrient-poor
lakes
Small ponds,
often devoid of fish
Food to chicks
Primarily fish
– also aquatic insects
Prey primarily taken in
breeding lake
Fish prey brought from
larger lakes or sea
– upto ca 10 km distance
(rarely more).
Fish stocks i
foraging waters
Perch is OK
Small-sized salmonid or
cyprinid fish
Water
transparency
Moderate-high Not equally important as
for BTD
Water
chemistry
Moderately acidic
Mostly good alcalinity
pH and alcanity lower
than in BTD lakes
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Population trends - Breeding performace
Indicators
• Population trend indices - Data from national bird monitoring scheme
• Breeding performance
- Mean number of large chicks per territory holding pair
• Breeding success (Mayfield method)
- Hatching success
- Brood rearing success (rearing at least one large chick)
• Chick survival
- % of broods with two large chicks
-
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Red-throated Diver (Gavia arctica) Population trend in Sweden (Swedish Bird Survey)
• Increase since mid-1970s, related to North and Central Sweden
• Historical decline – current status = depleted
• Recent decline in South Sweden
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North and North-central
Sweden (Norrland)
South-central Sweden
(Svealand and Dalsland)
South Sweden
(Sydsvenska Höglandet)
Red-throated Diver - South Sweden
0
0,5
1
1,5
2
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
TRIM
In
de
x
Population trend
Decline
-6.4 %/year***
0.55 per year
Decline*
12-37 pairs
0,00
0,20
0,40
0,60
0,80
1,00
1,20
1,40
1,60
1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014
Me
an
nu
mb
er o
f la
rge
ch
ick
s p
er
terr
ito
ry h
old
ing
p
air
Breeding performance
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North and North-central
Sweden (Norrland)
South-central Sweden
(Svealand and Dalsland)
South Sweden
(Sydsvenska Höglandet)
Red-throated Diver – South-central Sweden
Increase
+3.1 %/year*
0,00
0,20
0,40
0,60
0,80
1,00
1,20
1,40
1,60
1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014Me
an
nu
mb
er o
f la
rge
ch
ick
s p
er
terr
ito
ry h
old
ing
p
air
Breeding performance
0.62 per year
Decline*
74-159 pairs
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North and North-central
Sweden (Norrland)
South-central Sweden
(Svealand and Dalsland)
South Sweden
(Sydsvenska Höglandet)
Red-throated Diver – North and North-central Sweden
Increase
+5.3 %/year***
0,00
0,20
0,40
0,60
0,80
1,00
1,20
1,40
1,60
1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014
Me
an
nu
mb
er
of
larg
e c
hic
ks
pe
r te
rrit
ory
ho
ldn
ing
pa
ir
Inland breeders
Coastal breeders
Breeding performance Inland breeders
0.84 per year
Decline*
3-50 pairs
Coastal breeders
0.76 per year
No trend
12-57 pairs
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Breeding performance
1994-2015
Number of large
chicks, mean per pair and
year
Trend % of broods
with 2 large
chicks, mean per year
Trend
South Sweden 0,55 -* 36% 0
South-central
Sweden 0,62 -* 31% 0
North-central &
North Sweden
Inland
0,84 -* 42% 0
North-central &
North Sweden
Coast
0,76 0 53% 0
Foto: Jan Schützer
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Breeding success
1994-2015
Hatching
success,
mean per
year
Trend Brood
rearing
success, mean per
year
Trend Breeding
success, mean per
year
Trend
South Sweden 0.634 -*** 0.946 0 0.602 -***
South-central
Sweden 0,602 -* 0.900 0 0.543 0
North-central &
North Sweden
Inland
0.662 (-) 0.958 - 0.636 (-)
North-central &
North Sweden
Coast
0.678 -* 0.973 +* 0.658 0
Ph
oto
: Leif S
tran
db
erg
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Breeding performace - to summarize
• Higher in North and North-central Sweden, linked to
higher chick survival → better foraging conditions?
• Presumably too low to compensate for annual mortality
in South and South-central Sweden
• Declining trend in whole Sweden (except for coastal
breeders)
• Linked to declining trend in hatching success →
increased nest predation pressure?
-
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Is this the culprit?
Photo: Christer Brostam
• Records of nest predation by some species under recent increase
- Crane
- Whooper Swan
- Marsh Harrier
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http://atlas3.lintuatlas.fi/results/species/red-throated%20diver
FINLAND National survey in 2010
• 750-1500 pairs, re-assessment
rather than real changes ref
previous estimates
• Historical decline, recent
trends stable or slight
increase (although regional
declines)
• Good breeding performance, 1.13 chicks per pair, 2010.
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Ringing of Red-throated Diver
SWEDEN
• 1186 ringed birds, 1911-2016
• 91 recoveries (7.7 %), 89 ringed as chicks
FINLAND
• 987 ringed birds, 1974-2007, 1728 until 2016.
• 63 recoveries (6.4 %), 54 ringed as chicks (until 2007)
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Migration routes and wintering areas –
traditional view
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Annual mortality Age
class
SWEDEN:
Ringed before
1991
SWEDEN:
Ringed
1991-2005
SWEDEN:
All ringed
before 2005
FINLAND:
All ringed
before 2003
0-1 26,5% 37.7% 33.3% 23.3%
1-2 17.6% 50.0% 15.1% 62.2% 16.1% 57.4% 16.3% 51.2%
2-3 5.9% 9.4% 8.0% 11.6%
older 50.0% 37.8% 42.6% 48.8%
Number
of birds
34 53 87 43
Increased pre-breeding mortality?
? Real change
? Sampling artefact
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Red-throated Diver and offshore wind farms
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Photo: Mats Eriksson
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Red-throated Diver and
offshore wind farms
• Very scanty information
• Single records of
successful breeding close
to turbines (< 1km)
• But also indications of
disturbance / displacement /
avoidance
• More data needed - More pairs
- Longer follow-up periods
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Red-throated Diver and
offshore wind farms
Field surveys and monitoring
• Very scanty information
• Access of data
• Consistent methodology
• Quality of reports
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To summarise
• Recent increase (except for South Sweden) after long-term
historical decline = depleted
• Regional difference in breeding performance, lower in South and
South-central Sweden
….. where most likley too low to balance annual mortality
• Impaired hatching success – increased predation pressure…???
• Increased pre-breeding mortality…?????
• Very scanty information about breeding performance by pairs
nesting close to wind turbines
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To acknowledge
Projekt LOM To all volunteers – your field work is
the basic prerequiste for our work http://birdlife.se/sveriges-ornitologiska-
forening/fagelskydd/artprojekt/projekt-lom
The Alvin Foundation For financial support to field work
and participation in this workshop http://www.naturvardsverket.se/Stod-i-
miljoarbetet/Bidrag/Alvins-fond-for-fagelskydd/
The Swedish Bird Monitoring
Program For assistance with data http://www.fageltaxering.lu.se/
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THANK YOU
Photo: Matti Åhlund