Body weight and lipid reserves of American Black Ducks and Mallards during autumn

Abstract

A comparison of body weight and lipid reserves (weights of mesenteric and abdominal fat) of American Black Ducks (Anas rubripes) and Mallards (Anas platyrhynchos) during autumn was done to provide insight regarding the recent contemporaneous decline in Black Duck and increase in Mallard populations of eastern North America. Data were collected on 350 Black Ducks and 1477 Mallards shot by hunters in southwestern Ontario from September 24 to December 20, 1986. Date shot and fresh body weight were recorded, and the head, a wing, a foot, and the viscera were removed and frozen. Body weight and lipid deposits (weight of mesenteric and abdominal fat) were compared between the two species. The first principal component from an analysis of nine morphometric measurements was used as a covariate in subsequent analysis to remove variation in body weight and lipid deposits caused by differences in structural size. Although all age-sex classes of Mallards and Black Ducks stored lipids during the autumn, adult male and juvenile female Black Ducks stored less lipids than did their Mallard counterparts (P ≤ 0.01). Differences in lipid reserves during fall migration may be a proximal reason for the lower survival of adult male and juvenile Black Ducks compared with Mallards and may also influence the timing of intraspecific, and the rate of interspecifc, pair formation.