CHANGE IN BODY-MASS OF FEMALE COMMON GOLDENEYES DURING NESTING AND BROOD REARING

We measured body mass of female Common Goldeneyes (Bucephala clangula) during nesting on fish bearing lakes in northcentral Minnesota, in 19 82-1985. Median body mass during egg laying was 775 g. Female mass dur ing incubation varied among lakes and possibly years. Mass at the star t of incubation (698-715 g) was 10.7-11.0% greater than that at hatchi ng. Females regained most of the mass lost during incubation by the ti me they abandoned their class IIC or class III ducklings. Goldeneyes i n Minnesota weighed less at the start of nesting than those studied on predominately fishless Ontario lakes; proportional mass loss during i ncubation was also substantially less than that reported in Ontario (a pproximately 20%). Differences in body mass dynamics may be related to the relative ease of food acquisition during nesting; foods might be acquired more easily in more productive wetlands despite the presence of fish.