POPULATION-STRUCTURE AND CHANGES IN BODY-MASS AND COMPOSITION OF MALLARDS (ANAS-PLATYRHYNCHOS) WINTERING IN EDMONTON, ALBERTA

The population structure and changes in body mass and body composition of mallards wintering on the North Saskatchewan River in Edmonton, Al berta, were investigated from November 20, 1989 to March 15, 1990. The age composition of the population was biased in favor of juveniles (8 4%) and in favor of males (71%), possibly because of differential emig ration at the onset of winter. Ducks in the wild population lost 22-30 % of their live mass over winter. On average, males lost 75-76% of bod y lipids and 24-29% of proteins. Females lost between 66 and 92% of bo dy lipids and between 18 and 23% of proteins. These losses suggested t hat mallards wintering in Edmonton in 1989-1990 were insufficiently pr epared to meet the energy demands of spring migration and reproduction . Moreover, neither sex was able to maintain the level of protein inta ke needed to meet the protein costs of molt.