Winter dispersal and activity patterns of post-breeding black-legged kittiwakes Rissa tridactyla from Prince William Sound, Alaska

As colony-specific wintering ecology of small and medium-sized seabirds is poorly understood, it has been generally assumed that winter conditions have the same effect on all indi- viduals from any given colony. However, advances in global positioning technology now allow researchers to investigate movements of smaller seabirds. We tracked black-legged kittiwakes Rissa tridactyla using geolocator tags during the non-breeding season. Although kittiwakes as a group appear to be generalists with respect to overwintering strategy, our data indicate that indi- vidual birds are more specialized in their use of wintering habitat. Among birds tagged in the Gulf of Alaska, we identified 3 groups employing different wintering strategies: (1) resident birds that remain in the northern Gulf of Alaska; (2) coastal birds that remain within coastal and shelf waters but move as far south as California; and (3) pelagic birds that travel up to 1700 km offshore. Given that wintering conditions differ in widely spaced areas, the effects of winter on bird survival and body condition are likely not the same on all birds in a colony, as is often assumed. Activity data revealed that kittiwakes are almost entirely diurnal during the non-breeding season. We found significant differences in time allocation among wintering groups: birds that remained in the colony region spent less time loafing during the day and engaged in longer daytime flying and foraging bouts than birds that wintered farther from the colony. These differences suggest that wintering birds make trade-offs among travel distance, metabolic demands, and foraging quality.