Northward migration, molting locations, and winter residency of California breeding pigeon guillemots Cepphus columba

Abstract

Pigeon guillemots Cepphus columba are ubiquitous along the coasts of the eastern North Pacific, yet little is known about their winter migration patterns, habitat needs, and potential threats faced during the non-breeding period. We used 3 seasons of year-long light level data from tagged individuals to estimate the migration timing and winter residency of pigeon guillemots breeding on Southeast Farallon Island in California (USA). Light level data were combined with a movement model to estimate positions of tagged animals, revealing that individuals from this population undertook a coordinated coastal migration north in the fall, stopping at sites near Haida Gwaii in British Columbia (Canada), presumably during a flightless prebasic molt, before continuing north to stationary overwintering sites in coastal British Columbia and Southeast Alaska. Birds then made an uninterrupted migration south in the spring, returning to waters around Southeast Farallon in late March and early April. Wet/dry data indicated nocturnal resting on land during the breeding season and likely on the water throughout the non-breeding months. This is the first study to confirm the migratory patterns of pigeon guillemots from California, and highlights the importance of the waters of British Columbia and Southeast Alaska for the studied population and possibly other major populations of this species.