Changes in nesting success and breeding abundance of Spectacled Eiders Somateria fischeri in the Chaun Delta, Chukotka, Russia, 2003-2016

The Spectacled Eider Somateria fischeri is a rare sea duck confined to breeding in the Yukon-Kuskokwim Delta and Arctic coasts of Alaska and Russia. Almost nothing is known about its status and breeding biology in the Russian Arctic. Stratified systematic nest searches were conducted annually of Spectacled Eider nests on Ayopechan Island in the Chaun Delta, Arctic Russia during 2003-2016. Mean nest densities were stable during 2003-2009 but declined by 8.0% per annum during 2009-2016. Mean clutch size and annual female survival did not change over the same period, during which time annual nest survival and hatching success declined significantly. A simple three age-class matrix model estimated annual asymptotic population growth rate (lambda) using observed fecundity from the beginning (1.1 hatched chick per female, lambda = 0.864) and end (0.45 hatched chick per female, lambda = 0.828) of the study period. This confirmed that to stabilize this population required three immigrant recruits for every local recruit at the beginning of the study and nine towards the end. Declines in annual nest survival appear correlated with (i) declines in nesting Sabine's Gulls Xema sabini and Arctic Terns Sterna paradisaea with which nesting Spectacled Eiders associated and may have gained protection from predators, and (ii) marginally significant increases in large gull and mammalian predators at the site. Should current trends in nest density and fecundity continue, the survival of this breeding Spectacled Eider population is in jeopardy.