Migration trends for king and common eiders and yellow-billed loons past Point Barrow in a rapidly changing environment

Most of the king (Somateria spectabilis) and common eiders (S. mollissima v-nigra) nesting in northern Alaska and northwestern Canada migrate past Point Barrow, Alaska, during the spring and fall migration. Yellow-billed loons (Gavia adamsii) also migrate past Point Barrow and are a species of international conservation concern. Spring migration counts of eiders have been conducted approximately every ten years at Point Barrow since 1976, and indicated that both eider species experienced population declines of approximately 50% between 1976 and 1996, and that the declines had stabilized by 2004. Population estimates derived from migration counts have not been previously estimated for yellow-billed loons. We conducted spring counts of eiders and loons in 2015 and 2016 to obtain population estimates to compare with those from 1994, 1995, 2003, and 2004 in order to evaluate long-term and current trends. We estimated (95% confidence intervals) that 796,419 (304,011) king and 96,775 (39,913) common eiders passed Point Barrow in 2015, and 322,381 (145,833) king and 130,390 (34,548) common eiders passed Point Barrow in 2016. Both and king and common eider population estimates increased from 1994 through 2016, however, the increase over time was not significant (F < 5.07, P > 0.087, df = 1). Our population estimates for king eiders were very different between the two years of this study, possibly due to a very short and intense migration peak in 2016, resulting in a population count that was biased low because sampling periods did not adequately capture the peak of migration. The numbers of common eiders were similar between the two years, as well as for the 12 years since the previous count. Photo analysis of flocks indicated that observer counts were on average 4% lower than photo counts (paired t-test; |t| = 3.26, df = 297, P < 0.001) for flocks less than 1400 individuals (observer count). Estimates of yellow-billed loon populations were very variable and are biased low as numbers of loons passing Pt. Barrow were still high when our counts ended in late May. It is important that counts continue to be conducted for these species of conservation and subsistence importance, but that techniques be refined to reduce bias and variability, and to find solutions to the increasing difficulty of conducting a count from the shore-fast ice in spring.