We explored changes in seasonal distribution and behavior of waterbirds in the Strait of Georgia, Canada, in response to increased presence of a major avian predator, the Bald Eagle (Haliaeetus leucocephalus). Eagles were widespread and their increase through fall and winter coincided with migratory movements of waterbirds. Many species of waterbird used inshore waters in early fall when eagles were scarce. Diving birds moved away from inshore waters when eagles returned in late fall and winter, whereas dabbling ducks formed large flocks in inshore waters and spent proportionally more time being vigilant as winter progressed. Flock sizes and avoidance flight distances of scoters and dabblers, but not gulls, increased with proximity to eagles. Waterbirds did not alter vigilance with distance to eagles. We discuss our findings in context of management issues regarding apparent declines and importance of understanding indirect effects of predators on prey for wildlife monitoring.
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Vol. 99 • No. 1