Evaluating models of population process in a threatened population of Steller's eiders: a retrospective approach

The Alaskan breeding population of Steller's eiders ( Polysticta stelleri ) was listed as threatened under the Endangered Species Act in 1997 in response to declines in abundance and a contraction in their breeding and nesting range. Aerial surveys suggest the breeding population is small and breeds in highly variable numbers, with zero birds counted in five of the last 25 years. The primary objective of this research was to evaluate competing population process models of Alaskan breeding Steller's eiders through comparison of model projections to aerial survey data. To evaluate model efficacy and estimate demographic parameters, we used a Bayesian state‐space modeling framework and fit each model to counts from the annual aerial surveys using sequential importance sampling/resampling. The results strongly support that the Alaskan breeding population experiences population‐level non‐breeding events, and is open to exchange with the larger Russian‐Pacific breeding population. Current recovery criteria for the Alaskan breeding population rely heavily on the ability to estimate population viability. Our results provide an informative model of population process that can be used to examine future population states and assess the population in terms of the current recovery and reclassification criteria.