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Density-dependence in reproduction and survival:
Kyle Elliott, University of ManitobaJohn Elliott, Laurie Wilson, Environment Canada
Ken Stenerson, Kruger Forest Products
Linkages with chum salmon
N. Rich
Elliott et al 2011J Wildl ManageOn line
04/18/23
Bald Eagle Populations
1600 North Am popln 500,000+ ? 1600 Popln decline - persecution 1780 & habitat destruction 1780 25,000 - 75,000 birds 1940 BAEA Protect Act - some recovery 1947 Organochlorine era begins 1957 Reprod. failure documented in Florida 1960 < 450 nesting pairs in lower U.S. 1973 ESA in U.S., endang. status in some Cdn prov. 1975 DDT & other OC-pestic. use minimal (chlordane?) 1977 PCBs regulated (TSCA, CEPA) 1991 Lead shot ban for waterfowl in U.S. 1995 Endangered to threatened status > 5,000
100,000
1,0001600 2000
Objectives• Analyze long term data on eagles
breeding and wintering on south coast of BC
• Identify factors / mechanisms influencing trends.
Methods Counted eagles
– Breeding season by helicopter Occupied Territories Productivity
– Winter season with volunteers Christmas Bird Count Vancouver Raptor Census Coastal Waterbird Survey Midwinter Bald Eagle Count
Modelling– Leslie matrix
Density-dependence in mortality and reproduction
StudyArea
CBC Loc.
Km
Squamish
Harrison
Sampling Locations (1973-2010)
(1-12) = CBC Loc. = Breeding Counts = Salmon Spawning = Raptor Census
Breeding territories – Lower Fraser Valley
0
10
20
30
40
50
60
1985 1990 1995 2000 2005 2010
Year
Num
ber o
f ter
rito
ries
R2 = 0.57
R2 = 0.40
R2 = 0.39
0.2
0.4
0.6
0.8
1.0
1980 1985 1990 1995 2000 2005 2010Year
Prop
ortio
n of
Sub
adul
ts
0.0
0.5
1.0
1.5
2.0
2.5
Fecu
ndity
Density-dependence…but not through site-dependence
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
1996 1998 2000 2002 2004 2006 2008 2010
Year
Fecu
ndity
Early nests Late nests Reproductive Success Subadult Counts ● Subadult Mortality
2.4
2.6
2.8
3.0
3.2
3.4
3.6
1972 1982 1992 2002 2012
Year
Log
(eag
le n
umbe
r)
No. eagles wintering of south coast has increased to carrying capacity
Wintering eagle population on the south coast
050
100150200250300350400450
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35
Fraser delta Skagit Nisqually Oregon
0
500
10001500
2000
2500
3000
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35
Squamish Harrison Chum
0500
10001500200025003000
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35
Chilkat
N. Rich
Average no. of eagles counted at sites along Pacific coast
Weeks after Sept. 1
R2 = 0.18
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
-8 -4 0 4
Temperature (degrees C)
Resi
dual
log
(eag
les)
k
Adjusted eagle numbers on south coast of BC Increase with colder weather in Alaska
R² = 0.28,P < 0.003
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
4.2 4.6 5.0 5.4
Logarithm of chum salmon escapement
Loga
rith
m o
f eag
le n
umbe
rs
k
N. Rich
Eagle use days increase with chum availability at Squamish
0%
20%
40%
60%
80%
100%
Oct-Nov Dec-Jan Feb-Mar Apr-May Jun-Jul
Perc
enta
ge o
f die
t by
num
ber
Bird Mammal Fish
Percentage prey items in diet seasonally
0%
5%
10%
15%
20%
25%
30%
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Perc
enta
ge o
f tot
al d
eath
s
Bald Eagle Mortality: Percent by month (white) andcorrected for total present (dark)
AdultsSubadults
Causes of death for bald eagles, BC, 1989-2005
Fraser River Basin
1%5%
4%
4%
86%
Columbia River Basin
Source: Nehlsen et al., 1991 and Stanley et al., 1996
ExtinctHigh RiskModerate RiskSpecial ConcernUnthreatened
Loss of Salmon Stocks
04/18/23
400+ eagles spend time at the Delta landfill in winter
* Elliott, K et alWilson Bull, 2006
95% of time resting or drinking;
<5% foraging or feeding*
Alaska = Alaska Temperature BC = BC Temperature Observer = Number of observers
per count βR = Density-dependence in reproduction βS = Density-dependence in survival
AIC ranking of models for bald eagle populations, SW BC, 1973-2010
Impact on “prey” species?Bald eagles will harass and prey on colonial nesting species:
Great blue heron (Salish Sea—Vennesland and Butler 2005).
Double-crested Cormorant (Salish Sea, Middleton Island—Moul and Gebauer 2002).
Glaucous-winged Gull (Salish Sea—Sullivan et al. 2002, Hayward et al. 2010).
Dusky Canada Goose (Copper River—Anthony et al. 2004).
Common Murre (Middleton, Triangle, Tatoosh Island—Hipfner et al. 2001, Parrish et al. 2000).
Black-legged Kittiwake (Middleton Island) “Me and my gang”
Summary South coastal BC eagle breeding and wintering population
increased 4-6X over past 4 decades. Numbers of breeding and winter birds now “stabilized”
Density-dependence in reproduction and survival (model) Years with reduced salmon & cold (Alaska) winters leads to
reduced late winter survival & breeding females in poor body condition.
Elliott et al2011J Wildl Manageonline
THANKS!
Sandi Lee and Wayne Gardner for counting winter eagles
Many volunteers
F. Kovalchuk
Food supply (Elliott et al 2006, JRR)
Elliott et al.1998. JWM
British
Columbia
0 40 80 120 160
Kilometres
• Vancouver
• Seattle
StudyArea
Canada
USA
Bald Eagle Nest Success
Pinchi Lk.
Reference Lks.
SE Vancouver I.
Lower Fraser Valley
Fraser Delta
Clayoquot Sd.
Barkley Sd.
Powell River
Johnstone St.
Young / occupied nest0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
R2 = 0.68
R2 = 0.91
R2 = 0.93
0
5
10
15
20
25
30
35
40
45
0 50 100 150 200 250
Christmas Bird Count Totals
VRC
/CW
S av
erag
es
0
500
1000
1500
2000
2500
3000
MW
C to
tals
Vancouver Raptor Census Coastal Waterbird Survey Midwinter Eagle Count
Double-survey techniques show >90% repeatability
Wintering eagles
British Columbia (breeding and winter):30% increase from 1960s to 1980s
(Vermeer et al. 1989)
British Columbia (winter):“Either stable or increasing” (Blood and Anweiler 1994)
British Columbia (winter):“Generally stable” (Campbell et al. 1990)
British Columbia (winter):No change 1982-1997 (Buehler 2000)
Washington (breeding):Increased 10.1% per year 1980-1998 (Watson et al. 2002)Increased 1962-1995, stable to 1998 in San Juans (Watson et al. 2002)
Washington (winter, Skagit):Doubled 1987-1992, then stable (Dunwiddie and Kuntz 2001)
British Columbia’s eagles
Issue of native harvest of eagles for ceremonial items
Prey energy and productivity atBC coastal eagle nests
0
0.4
0.8
1.2
1.6
2
2.4
500 1000 1500 2000 2500 3000 3500 4000
Prey energy/day/eaglet
Youn
g/O
cc. T
err.
r = 0.63
North of millSouth of millBarkley Sound
00.05
0.10.15
0.20.25
0.30.35
Rain No rain Rain No rain
East WestPrey
del
iver
ies
per h
our
Elliott et al. 2005. JRR
Prey delivery rate and weather, SW BC eagles(Elliott et al. 2005. J Rap Res)
Indication: Areas lacking an adequate and stable prey base, and which are subject to regular episodes of wet spring weather are likely to contain Bald Eagle sink populations
Panoramia
Elliott et al. 2006. Wilson J Ornithol
Bald eagles and landfills
Thyroid Hormones
Regulate growth and development, particularly neurological system
Important to immune system function
Regulate metabolism
Cardiovascular effects
deiodinases
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