Population ecology of Pacific common eiders on the Yukon-Kuskokwim Delta, Alaska

Abstract

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 or less] 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 ([lamda]) indicated that the YKD population was stable to slightly increasing during the years of the study (range [lamda]: 1.02-1.05 (CI: 0.98-1.11)), and would respond most dramatically to changes in adult female survival. However, historical fluctuations in [lamda] 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.