Common eider wintering trends in Nova Scotia, 1970–2019

Common eiders Somateria mollissima have been a focus of conservation and management efforts in eastern North American for over a century; however, the complex population structure and multiple subspecies make assessing the status of populations challenging. The coastlines of Nova Scotia, Canada, are an important wintering area for common eiders, and significant harvests of common eiders occur in the province. We analyzed trends in the number of wintering common eiders using the coasts of Nova Scotia from dedicated waterfowl surveys flown since 1970, and every year since 1992. We used Generalized Additive Models to assess the apparent non-linear trends in the counts of common eiders over the past 50 y. We found that numbers of common eiders wintering in Nova Scotia increased from 1970 to the early 2010s, with strong growth in the 2000s (peaking at 7% growth/y). Since the early 2010s, the growth has stopped, and the numbers are now declining. Recent declines in the population wintering in Nova Scotia corroborate other evidence that common eiders are declining in the region, and may also indicate distributional shifts of common eiders in eastern North America.