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Advisor(s)
Abstract(s)
Migration is a widespread phenomenon among birds and is likely to be subject to strong selective pressures. Birds’ annual
routines and behaviors might be expected to change during their diff erent life history stages, resulting in diff erent, agerelated
migration patterns. However, although migration has been the subject of many publications, age-related diff erences
in migration have received little attention. Th e present study examined age-related changes in individual migration
habits in lesser black-backed gulls, Larus fuscus. We analyzed data from 10-year (1998–2007) color-ringing project in NW
England, comprising more than 10 000 ringed individuals. Our results showed a latitudinal cline in age structure across
the wintering range, with adults and gulls in their fi rst breeding year wintering closer to the breeding grounds. Supporting
this result we observed that individuals, as they get older, changed the migration behavior and winter closer to the breeding
areas. Interestingly, we found no diff erences in survival rates across the wintering grounds. Th us diff erences in survival rates
can not account for the latitudinal cline in age structure, and the observed fi ndings seem to be best explained by the arrival
time hypothesis, based on a mechanism whereby individuals are able to change their migratory behavior as result of the
onset of sexual maturity and associated mating pressures.
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Keywords
Citation
Oikos, 119, 946–951
Publisher
Nordic Ecological Society