Movements of Pre-migratory Surf and White-winged Scoters in Response to Pacific Herring Spawn

Lewis, T L.
Esler, Dan
Boyd, W.S.
Centre for Wildlife Ecology, Simon Fraser University
Canadian Wildlife Service - Pacific and Yukon Region
Publication Date: 

Condo (2007) Volume: 109, Issue: 1, Pages: 216-222

Winter diets of Surf (Melanitta perspicillata) and White-winged Scoters (M. fusca) are composed primarily of bivalves. During spawning of Pacific herring (Clupea pallasi) in early spring, scoters shift their diets to herring eggs. Using radiotelemetry, we contrasted scoter foraging behaviors between winter and herring spawning periods. Scoters increased their dive durations during herring spawning, likely to maximize the amount of roe consumed per dive; in winter, dives were typically terminated upon clam capture. Scoters spent approximately 5011,, less time foraging (min underwater hr(-1)) and decreased their dive rate (dives hr(-1)) by 70% when feeding on roe. The observed reduction in time spent foraging was presumably caused by the abundance of herring eggs, and thus a reduction in prey search-time. Scoters were able to meet energetic requirements with reduced effort, despite potentially increased demands related to spring fattening. Less time spent foraging may also allow more time for premigratory courtship behaviors.