Cooperative Fish and Wildlife Research Units Program: Oregon
Education, Research and Technical Assistance for Managing Our Natural Resources

Double-crested cormorants (Phalacrocorax auritus) have been identified as the source of significant mortality to juvenile salmonids (Oncorhynchus spp.) in the Columbia River Basin. Management plans for reducing the size of a large colony on East Sand Island in the Columbia River estuary are currently being developed. We evaluated habitat enhancement and social attraction as non-destructive techniques for managing cormorant nesting colonies. We tested these techniques on unoccupied plots adjacent to the East Sand Island cormorant colony. Cormorants quickly colonized these plots and successfully raised young. Cormorants were also attracted to nest and raised young on similar plots at two islands ca. 25 km from East Sand Island; one island had a history of successful cormorant nesting and the other was a site where cormorants had previously attempted to nest, but were unsuccessful. On a third island with no history of cormorant nesting or nesting attempts, these techniques were unsuccessful in attracting cormorants to nest. Our results suggest that some important factors influencing attraction of nesting cormorants using these techniques include history of cormorant nesting, disturbance, and presence of breeding cormorants nearby. These techniques may be effective in redistributing nesting cormorants away from areas where fish stocks of conservation concern are susceptible to predation, especially if sites with a recent history of cormorant nesting are available within their foraging or dispersal range.