Population Ecology of Pacific Common Eiders on the Yukon Kuskokwim Delta, Alaska

Author(s): 
Wilson, Heather M.
University of Alaska Fairbanks - Dept of Biology and Wildlife
Publication Date: 
2007

Knowledge of ecological factors that influence birth, death, immigration, and emigration provide
insight into natural selection and population dynamics. Populations of Pacific common eiders
(Somateria mollissima v-nigrum) on the Yukon-Kuskokwim Delta (YKD) in western Alaska declined by
50-90% from 1957 to 1992 and then stabilized at reduced numbers from the early 1990’s to the
present. This study investigates the primary underlying processes affecting population dynamics of
Pacific common eiders, with the goals of understanding factors that may have led to the observed decline
and subsequent stabilization, and providing tools from which conservation, management, and
recommendations for future research can be drawn.
I examined variation in components of survival and reproduction in order to test hypotheses about
the influence of specific ecological factors on life history variables and to investigate their
relative contributions to local population dynamics. These analyses include data I collected from
2002 to 2004, in addition to historical data collected from
1991 to 2001. Apparent survival of adult females was high and relatively invariant, while
components of reproduction were low and variable, both within and among individuals. Timing of
nesting and seasonal declines in clutch size and nest survival indicated that females in the early
and mid parts of the breeding season produced the highest numbers
of offspring; suggesting directional selection favoring early nesting. Probability of a nest
containing ≥ 1 nonviable egg was positively related to blood selenium concentrations in hens, but
no other contaminant-related reductions to life history variables were found.
All estimates of population growth (λ) indicated that the YKD population was stable to slightly
increasing during the years of the study (range λ: 1.02-1.05 (CI: 0.98-1.11)), and would respond
most dramatically to changes in adult female survival. However, historical fluctuations in λ were
primarily explained by variation in reproductive parameters, particularly duckling survival.
Practical options for increasing adult survival currently may currently be limited. Thus,
enhancing productivity, particularly via methods with simultaneous positive effects on adult
survival (e.g., predator removal), may offer a more plausible starting point for management aimed
at increasing population growth.

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