Long‐term trends in the survival rates of adult female Common Eider Somateria mollissima at three colonies in Iceland

Abstract

Identifying temporal and spatial patterns in demography is critical to understanding long‐term fluctuations in population size. Common Eider Somateria mollissima numbers have shown a long‐term decline, resulting in the species being uplisted in 2015 to ‘Endangered’ within European Union countries. Obtaining improved estimates of survival rates of Common Eiders (and other seaducks) has been identified as a priority to improve our understanding of the demographic causes of the observed global decreases in population size and to inform conservation efforts. In this study, we used long‐term (1982–2017) mark–recovery data on 3018 individuals from three breeding colonies in Iceland to quantify the spatial and temporal variation in the annual true survival rates of adult female Common Eider. Model comparison using an information‐theoretic approach indicated that true survival and recovery rates varied between years and colonies but showed no consistent temporal pattern across the three colonies. Geometric mean (± se) annual true survival across our three breeding colonies was 0.916 ± 0.017 (95% confidence interval (CI) = 0.819–0.961), with a mean life expectancy of 11.8 years (95% CI 5.4–25.2). Our survival estimates were relatively high compared with those reported previously for many other Common Eider populations, which may reflect their protected status, low predation pressure and high food availability on Iceland and its surrounding waters. Our findings provide spatially and temporally explicit demographic information needed to help conservationists understand the local and global declines in Common Eider populations.