Moult intensity and chronology of Tundra Swans during spring and fall migration at Long Point, Lake Erie, Ontario

Abstract

Moult intensity and chronology in staging Eastern-Population (EP) Tundra Swans (Cygnus columbianus columbianus) were studied during spring in 1999 and 2000 (n = 35) and during fall in 1999, 2000, and 2001 (n = 47) at Long Point, Lake Erie, Ontario. To test for age, sex, and seasonal differences in moult intensity, 20 feather regions were scored according to the proportion of growing feathers. Adult, subadult, and juvenile Tundra Swans moulted contour feathers at low intensities during spring and fall. Males and females of all three age classes had similar patterns and intensities of moult during spring and fall. Shared costs of incubation and brood rearing, perennial monogamy, and lack of a breeding plumage could be some of the pressures selecting for intersexual similarities in feather replacement during migration. Adult, subadult, and juvenile Tundra Swans moulted more intensively during fall than spring. Larger lipid reserves and seasonal dietary differences may allow fall-staging Tundra Swans to moult more intensively than spring-staging birds at Long Point. Overlap of nutritionally costly events (moult and migration) may be necessary as Tundra Swans spend half of their annual cycle on spring and fall staging areas. However, reduced daily nutritional costs associated with moulting at low intensities and migrating slowly apparently permits the overlap of these two life-cycle events.