migration strategies and winter movements of king eiders...
TRANSCRIPT
Migration strategies and winter movements of King Eiders in the
Bering Sea
Steffen Oppel, Abby Powell
Ala
ska
Bird
Con
fere
nce
8
Febr
uary
200
6
AK
Bering Sea
• King Eiders spend 10 months/year at sea
• AK birds migrate to Bering Sea in winter
• Wintering range spans 15° latitude
Background
Background
• migration trade-off:
distance environmental conditions
• birds wintering further north face harsher climate
• more likely to be forced to move in winter
Questions
• What proportion of the population uses >1 wintering site?
• Are winter movements more common at higher latitude?
Methods
• 80 birds fitted with satellite transmitter in June 2002-2005
• data filtered for best location per duty cycle
• one location every 2-7 days
• classification of seasons based on movement rate
King Eider seasons
Molt migration (July – September)
King Eider seasons
Wing molt (August – October)
King Eider seasons
Fall migration (October – December)
King Eider seasons
Winter period (November – March)
? ?
King Eider seasons
Spring migration (April – June)
0
1000
2000
3000
4000
5000
600004 04 04 04 04 04 04 04 04 04 04 04 04 04 04 05 05 05 05 05 05 05 05 05 05 05 05 05
0
50
100
150
200
250
300
350
WingMolt
Methodscu
mul
ativ
e di
stan
ce fl
own
(km
) Movem
ent rate (km/day)
Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May JunMolt
MigrationFallMig.
Winterperiod
SpringMigrationAll distances calculated are minimum values
molt area
winter area
stopover
Results: fall migration
• 43.4% of tracked King Eiders have no fall migration
• three strategies of fall migration1) none (43.4%)2) short, one step (27.7%)3) long, multi-stage (28.9%)
• birds wintering in AK and RUS use strategies equally
Results: winter movements
• winter period 56 – 280 days depending on strategy
• 56.9% of tracked birds used >1 wintering site
• mean distance traveled in winter 644 km (± 453 km SD)
• large variation, range 46 km – 1947 km
Results: winter movements
Initial wintering latitude (deg N)
Num
ber o
f win
ter m
ovem
ents
R2 = 0.0232
0
1
2
3
4
5
50 52 54 56 58 60 62 64 66
Results: winter movements
Initial wintering latitude (deg N)
dist
ance
trav
eled
in w
inte
r (km
)
dist
ance
per
day
(km
/day
)
0
200
400
600
800
1000
1200
1400
1600
1800
2000
50 55 60 65
R2=0.16
0
200
400
600
800
1000
1200
1400
1600
1800
2000
50 55 60 650
5
10
15
20
25
R2 = 0.0003
Results: winter movements
• winter movements not explained by:
• latitude (p = 0.159, Lin. Regr.)• year (p = 0.988, ANOVA)• sex (p = 0.815, ANOVA)
• winter movements differ between migration strategiesno fall migration > one-step fall migration (p = 0.014)
Discussion
• winter movements occur in > 50% of adults
• potential explanation for low spatial genetic structure(Pearce et al. 2004)
• causes not related to latitude, year or sex:• food depletion?• age and experience of the bird?• social factors?
• temporal resolution insufficient to track movements? (Bump and Lovvorn 2004: Spectacled Eiders fly >2000 km in winter)
Future directions
• explore local weather correlates that may cause movements
• track juveniles and successfully breeding females
• explore spatial and temporal availability of benthic prey
Acknowledgements
US Fish and Wildlife ServiceMinerals Management ServiceSea Duck Joint VentureCoastal Marine InstituteNorth Slope BoroughConoco Phillips, AKUSGSABR, Inc.Service Argos, Inc.Microwave Telemetry, Inc.German Academic Exchange ServiceTroy Ecological Research Associates, Inc.Alaska Cooperative Fish and Wildlife Research Unit
Robert SuydamDave DouglasRebecca McGuireLaura PhillipsFalk HuettmannCheryl Scott
…and a large number offield assistants…
Questions?
photos by Kim Hanisch
pictures © Kim Hanisch and Keith Brady