Postbreeding ecology of White-winged Scoters (Melanitta fusca) and Surf Scoters (M. perspicillata) in western North America: wing moult phenology, body mass dynamics and foraging behaviour.

Waterfowl undergo simultaneous remigial moult, in which flight feathers are shed and then re-grown synchronously. Nutrient and energy demands and vulnerability to predation may be elevated during remigial moult, suggesting that this stage of the annual cycle could pose a constraint on population dynamics. I studied remigial moult in two sea ducks, Surf Scoters (Melanitta perspicillata) and White-winged Scoters (M. fusca), in southeast Alaska and the Salish Sea to evaluate evidence of temporal, energetic or nutritional constraints. Scoters exhibited a relatively long flightless period and high inter-individual variation in timing of moult, suggesting there were not strong temporal constraints during this phase of the annual cycle. Increasing body mass during the feather growth period indicated that scoters met costs of moult without relying on endogenous reserves and they did so at moderate levels of foraging effort, strong evidence of lack of energetic or nutritional constraints.