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