Molt in the Annual Cycle of Canvasbacks

Abstract

Abstract We studied the intensity of molt of capital, down, and contour plumages of male and female Canvasbacks (Aythya valisineria) from late fall through winter, spring migration, and nesting. Molt intensities in both juvenile and adult males were highest among arriving fall migrants and during prewinter fat deposition, and molt in juvenile males increased during early spring migration. Among females, capital molt was high among arriving migrants in fall, and molt of all plumage types increased during spring migration and courtship. Paired females tended to molt more heavily than unpaired females during spring migration, but many females initiated intensive prebasic molt before pairing. Molt in females peaked in spring migration and early breeding, concurrently with accelerated fat storage and ovarian growth. Capital and contour molt in females decreased during laying and essentially ceased during incubation, perhaps to mitigate energetic constraints during these periods. Prewinter nutrient storage appeared independent of molt intensity, except for body protein among juveniles. During spring migration, molt intensities were greater in adult females with higher levels of body fat and protein, indicating that molt did not necessarily precede or interfere with nutrient storage. We suggest that outside the laying, incubation, and wing molt periods, the energetic costs of molt in Canvasbacks are not sufficient to mandate temporal separation of molt from nutrient storage, migration, courtship, or early stages of rapid ovarian growth.