Second North American Sea Duck Conference - Patuxent Wildlife ...

SECOND NORTH AMERICAN SEA DUCK CONFERENCE
POPULATION DYNAMICS OF PACIFIC COMMON EIDERS
ON THE YUKON-KUSKOKWIM DELTA, ALASKA
Heather Wilson¹, Abby N. Powell¹, Paul L. Flint², and Tina L. Moran 3
¹US Geological Survey, Alaska Cooperative Fish and Wildlife Research Unit Department of
Biology and Wildlife, University of Alaska, Fairbanks, AK 99775; fthmw@uaf.edu
²US Geological Survey, Alaska Science Center, Anchorage, AK 99503
3 US Fish and Wildlife Service, Yukon Delta National Wildlife Refuge, Bethel, AK 99559
Pacific common eiders (Somateria mollissima v-nigrum) have undergone precipitous declines in
Alaska and throughout western North America, prompting management concern. We incorporated
past data collected by the Yukon Delta National Wildlife Refuge (YDNWR) and USGS Alaska Science
Center (ASC) with more intensive recent studies, to investigate the primary underlying processes
affecting population dynamics of breeding Pacific common eiders on the Yukon Kuskokwim Delta
(YKD) in western Alaska. We estimated survival and productivity of adult females and examined
factors affecting these vital rates across a range of breeding areas from 1991-2004. We used 10 years
of capture-recapture data, consisting of 268 recapture events from 272 uniquely marked individuals,
to investigate temporal, geographic, and environmental patterns in adult female survival. Consistent
with life-history predictions for long-lived species, we found little support for variability in apparent
survival; mean: 88% (SE ± 2%). However, recapture rates varied markedly across years and study
areas (range: 2% to 61%), averaging 38%. To examine productivity in Pacific common eiders we
used data from 2114 individual nests over 14 years of study. We found productivity to be highly
variable; timing of nest initiation, clutch size, and patterns of daily nest survival all varied across
sites and years. Our best model suggested that daily nest survival decreased with later initiation
date and increased with age of the nest. Estimated nest success ranged from 1 to 83% among study
areas and years and average productivity was 0.98 female ducklings per hen per year. Based on
local demographic rates, we developed a population model and calculated the population growth
rate (λ) and stable age distribution. We used perturbation analyses to examine the relative effects
of survival and reproduction on λ. We used viability analyses to examine probability of population
persistence for 50 to 100 years into the future. Our goal was to provide local and regional managers
with modeling tools for use in future studies and to aid in developing effective management strategies
for the long-term viability of Pacific common eiders on the YKD.
18 ANNAPOLIS, MARYLAND, USA NOV. 7-11, 2005