Body and Organ Mass and Body Composition of Postbreeding Female Lesser Scaup

Abstract

Abstract Changes in body and organ mass and body composition of postbreeding female Lesser Scaup (Aythya affinis) were investigated in the prairie-pothole region of southwestern Manitoba. Body mass was lowest during the wing molt and peaked during the migratory period. Most digestive organs gradually increased in mass through the postbreeding season. Lipid reserves remained relatively constant from the preflightless through the postflightless periods (x̄ = 43 g). The marked increase in lipids in the migratory period (x̄ = 183 g, P < 0.05) corresponded with premigratory hyperphagia. Time spent feeding explained 87% of the variation in lipid levels during the postbreeding season. Protein reserves declined with the onset of wing molt (P < 0.001) and increased during the postflightless period (P < 0.05). Breast muscle mass followed a similar pattern and was strongly correlated with molt intensity (r = 0.799, P < 0.001). Protein reserves, in particular the breast muscles, provide at least part of the protein required for feather production. Low body mass and lipid reserves during molt may not indicate energetic or nutritional stress but, alternatively, may be part of a postbreeding strategy to minimize energy demands and to reduce the length of the flightless period.