Abstract
Abstract Niche overlap and resource partitioning have seldom been investigated in the marine habitats of seabirds but are obvious determinants of community and population status. We investigated interspecific differences in densities and spatial aggregations of seabirds during summer (June–August) off southwest Vancouver Island, British Columbia. Two 300-m-wide parallel transects were sampled along 66.6 km of shoreline in 1993–1996, centered 200 m and 600 m from shore. Analysis focused on the threatened Marbled Murrelet (Brachyramphus marmoratus) and three other fish-eating alcids. Densities of Marbled Murrelets were among the highest reported at sea in the species' range; they were concentrated close to shore (>75% within 0.6 km and virtually all within 2.0 km of shore), usually in water <20 m deep, and showed strong fidelity to certain sectors along the coast from year to year. Common Murres (Uria aalge) and Rhinoceros Auklets (Cerorhinca monocerata) were not as closely associated with nearshore habitat...
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