Habitat quality and metapopulation dynamics of Black-legged Kittiwakes Rissa tridactyla

Neighboring colonies of Black-legged Kittiwakes Rissa tridactyla in Chiniak Bay, Alaska, exhibit contrasting long-term trends in productivity and population size that are consistent with variation in habitat quality at a fine spatial scale. Fine-grained reproductive variability of kittiwakes in Chiniak Bay suggests that patchy food abundance does not drive patterns of dispersal, recruitment and colony dynamics within this metapopulation. We found that, among-colonies, variability in productivity was better explained by differences in cliff elevation than by differences in size, age or proximity to Glaucous-winged Gull Larus glaucescens colonies. Although lacking direct evidence, we speculate that localized predation may underpin the "elevation effect" for two reasons: anecdotal observations suggest that large aerial predators prefer to roost on and hunt from taller cliffs; and coincident with a marked increase in these predators from historically low levels, the distribution of kittiwakes has shifted from long-established colonies on taller cliffs to newly-formed colonies on shorter cliffs. Regardless of origin, differential productivity can affect population dynamics of seabird colonies either through natal recruitment or by shaping patterns of dispersal between colonies within the wider metapopulation. Performance-based conspecific attraction posits that if chick production is a reliable predictor of habitat quality, then prospective breeders can benefit by preferentially recruiting into colonies with above-average productivity. Despite finding that differences in productivity among kittiwake colonies were predictive of future habitat quality, we found that conspecific attraction could not explain differential population trends of colonies. In contrast, we found that the most important drivers of population dynamics of kittiwake colonies within Chiniak Bay were natal site fidelity and intrinsic differences between colonies that are unrelated to productivity.