Comparing demographic parameters for philopatric and immigrant individuals in a long-lived bird adapted to unstable habitats.

Theoretical models about the benefits of philopatry predict that immigrant fitness can be higher, lower or similar to that of philopatrics depending on habitat heterogeneity, dispersal costs, distance between patches or population densities. In this study, we compared transience rates, local survival and recruitment among philopatric and immigrant individuals of Audouin's gull Larus audouinii, a long-lived bird with high dispersal capacities. Several previous studies have shown that these capacities were probably the result of adaptation to unstable and highly discrete habitats; hence, we tested the hypothesis that fitness components for philopatrics and immigrants were similar. During 1988-2006, ca. 27,800 chicks were marked in 31 colonies in the western Mediterranean metapopulation, and more than 52,000 resightings were made in a single, high-quality colony, to estimate local demographic parameters by capture-recapture analyses. Results suggest that, even though parameters related to site-tenacity (e.g. recapture rates) were higher for philopatrics than for immigrants, survival and recruitment were fundamentally similar. Small differences between philopatrics and immigrants were probably influenced by a highly suitable habitat at the study site, which reduced dispersal costs for immigrants; furthermore, the similarities in most fitness components were also probably the result of a life-history strategy of a species living in unpredictable, unstable habitats with high emigration rates among local populations, and with a relatively low cost of dispersal.