Changes in Body Composition of American Black Ducks Wintering at Chincoteague, Virginia

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Abstract
Fifty-nine American Black Ducks (Anas rubripes) were collected during early, mid-, and late winter 1985-1986 at Chincoteague, Virginia to assess overwinter changes in physiological condition. Lipid Index (LI = grams lipid/gram nonlipid dry carcass .times. 100) values of adult males were relatively high throughout winter, whereas LI values of both female age classes were low in early winter, peaked by midwinter, and remained high into late winter. Juvenile females had consistently lower LI values than adult females, indicating that juvenile females may be physiologically disadvantaged during winter. Protein mass did not vary over winter, but tended to be less in juvenile females than adult females. In contrast, Reinecke et al. (1982) found that lipid and protein masses of female American Black Ducks (both age classes) wintering in Maine decreased between fall and winter. This disparity may be explained by latitudinal differences in winter severity and diet. We argue that improved physiological condition, as a result of wintering farther south, may influence overwinter survivorship more strongly than reproductive potential during the subsequent spring.