Dynamics of seasonal movements by a trans-Pacific migrant, the Westland petrel

Knowledge of the dynamics of long-distance migrations of pelagic seabirds is limited. Recent advances in tracking technology have yielded detailed, continuous accounts of the movements of individual seabirds over large spatial and temporal scales. We studied the timing of migration and year-round distribution of the Westland Petrel (Procellaria westlandica), listed by the IUCN as vulnerable, with miniature archival light loggers (geolocators) deployed on 10 incubating birds breeding in 2007 at Westland, New Zealand. We retrieved data from eight Westland Petrels, indicating the birds migrated in November directly east 7000 km from the coast of New Zealand to South American waters in 6 days (range 47), then returned the following April in 10 days (range 813). The durations of an individual's outward and return flights and the dates of its outward and return migrations were positively correlated. During their journeys east and west, birds spent on average (SD) 9.9% (9.7) and 17.2% (12.0), respectively, of their time on the water. There was also considerable variation in individuals' foraging areas: while breeding, birds used three major coastal areas <1200 km from their colony; during the nonbreeding period, six birds remained off the south coast of Chile, while two others continued their migration through the Drake Passage to waters off southern Argentina. These results expand the known distribution of the species, identify new key foraging areas, and show patterns of outward and return migration behavior consistent in individuals.

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