Geographic and temporal variation in diet of wintering White-winged scoters
White-winged scoters (Melanitta fusca) are a species of sea duck that spend much of their time in northern marine environments. This paper investigates how dietary changes occur in response to changing availability of prey and the effect of those dietary changes on scoter condition and reproductive success, among other variables.
The researchers measured the dietary composition of white-winged scoters in five locations along the Pacific coast of Washington and British Columbia. The measurements took place during mid and late winter, when scoters exhibit high site fidelity. The sites varied in latitude, water depth, and wind and wave exposure, which may influence foraging behavior and diet composition.
Infaunal bivalves were the most common prey at each site, though species and size varied. The Dogfish Banks site had the highest prey species richness, and over 20 species of bivalves were consumed across the five sites. At Dogfish Banks and Chatham Sound, scoter diets were more diverse in late winter, while their consumption at other sites remained fairly uniform.
The study supports past results, which indicate that infaunal bivalves are an important type of prey for white-winged scoters. However, at Dogfish Banks, scoters showed flexibility later in the winter, consuming species such as fish and echinoderms that have not previously been documented as a component of their diet. Varnish Clams, an invasive species, have crowded out many native bivalves, resulting in a loss of diversity in scoter diet.
The research demonstrates the importance of bivalve habitats for poulations of white-winged scoters, which have declined in recent decades.
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