The nearshore and offshore waters of southern New England provide some of the most
important wintering habitat for sea ducks in North America. Understanding changes in sea duck body
composition during winter could provide insights into current habitat quality and potential effects of
anthropogenic disturbances on the body condition of sea ducks. We used the deuterium dilution method, a
nonlethal approach, to investigate intraseasonal variation and differences between genders in body
composition of 86 adult common eiders (Somateria mollissima) during winter (2011 and 2012) in southern
New England. Both male (n¼39) and female (n¼47) eiders increased fat mass by 75% in late winter
compared with early winter. Wet lean mass of males remained constant throughout the winter, while that of
females decreased by 10%. These seasonal increases in fat stores of eider suggest that birds were able to secure
adequate resources to improve their body condition over winter. Our estimates of body composition of eider
during winter in southern New England can be used as a baseline when conducting future research to evaluate
effects of anthropogenic disturbance and disease. Ó2016 The Wildlife Society.
KEY WORDS body composition, common eider, deuterium dilution, Somateria mollissima, southern New Englan