Testing for Geographic Variation in Survival of Spectacled Eider (<i>Somateria fischeri</i>) Populations in Chukotka, Russia and the Yukon-Kuskokwim Delta, Alaska
Information on variation in survival among geographically distinct breeding populations can produce valuable insights about the population dynamics of a species. The Yukon-Kuskokwim Delta sub-population of Spectacled Eiders in Alaska decreased precipitously between the 1950s and 1990s. Causes for this decline are unknown but may be attributed to low female survival due to predation and lead exposure on the breeding grounds. From 2014 to 2015, we compared annual survival probabilities of Spectacled Eiders on Kigigak Island in the Yukon-Kuskokwim Delta, Alaska, and Ayopechan Island in the Chaun Delta, Chukotka, where similar field protocols were implemented. A Cormack-Jolly-Seber maximum likelihood approach was used to estimate apparent survival (φ) and recapture probability (p) from mark-resight data. We tested a) whether Russian and Alaskan sub-populations differed in their survival rates, b) whether survival varied annually, and c) whether survival followed an increasing or decreasing trend over time at either site. We found no evidence for differing survival between the two breeding areas when mean survival across years was compared, and we did not find strong evidence for a linear trend in survival over time at either site. Furthermore, our data supported models with annually varying survival at Kigigak Island and constant survival at Ayopechan Island. Sample size constraints precluded estimates of annual survival at Ayopechan Island. Our finding of no difference in mean survival between sites lends support to the idea that survival may be a function of conditions on the wintering grounds.
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