Abstract
Body mass and body composition of 27 adult Velvet Scoters (Melanitta fusca) were studied. These birds were collected from January to March in the Gulf of Gdańsk, Poland. Body mass, fat, and protein contents of both males and females decreased significantly between mid and late winter, possibly because of a physiological process or a result of worsening environmental conditions. In mid-winter, the mean body mass of males and females did not differ significantly, whereas in late winter the difference in body mass between sexes became prominent. There was no difference in fat mass between the sexes, but females had higher lipid indexes despite their smaller size. The lack of expected fat mass increase in late winter may be due to the spring migration strategy of Velvet Scoters, which apparently opt to fly short distances rather than make long non-stop flights after departure from the Gulf of Gdańsk. Body mass was the best predictor of fat mass accumulated by Velvet Scoters wintering in the Gulf of Gdańsk.