Individual consistency in migratory behaviour of a pelagic seabird

Many animals migrate between breeding and wintering areas; however, whether each animal behaves consistently in space and time between consecutive years is less well understood. Furthermore, previous breeding state (successful or failed) is often not considered when attempting to understand consistent individual differences in behaviour that are likely to impact upon the subsequent behaviour. Between 2006 and 2010, we used geolocators to track the migratory movements of a pelagic seabird, the streaked shearwater Calonectris leucomelas, with individuals (N=46) being followed for two years or more, including 23 birds that had chicks in two seasons and 23 birds in just one season. All individuals, except for one bird, migrated to the same broad wintering areas, and their migratory route as well as the centre of wintering distribution did not change in relation to the previous breeding outcomes. Migration schedules (dates of departure from the breeding colony, southward and northward migrations, and first return to the colony) did not differ significantly between years for individuals that had chicks during both years, while failed individuals left the breeding colony and appeared to start the southward migration at an earlier date than the previous successful year. Nonetheless, the timing of the southward migration was consistent within individuals, including both males and females, over successive years regardless of the previous breeding outcome, and also the timing of first return back to the colony for females that had chicks in the both previous years and eggs in the both following season. This may imply the existence of individual-specific broad time schedules, possibly a circannual rhythm, though ecological conditions might affect the exact timing of the actual departure event. Our results present evidence for high levels of individually consistent behaviour for this pelagic seabird outside the breeding season.

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