Apparent Survival and Fecundity of Sympatric Lesser Black-Backed Gulls and Herring Gulls with Contrasting Population Trends

Abstract

We investigated apparent survival (i.e. survival confounded by permanent emigration) on the basis of a colour-ring programme in which individual Lesser Black-backed Gulls Larus fuscus and Herring Gulls Larus argentatus could be monitored over time. The work was conducted in a large, mixed colony in the western Wadden Sea (Texel), where measures of fecundity were collected simultaneously. In Herring Gulls, we found a mean apparent annual adult survival of 79% in females and 86% in males. Additive year effects rather than sex provided highest model support in Lesser Black-backed Gulls, in which apparent survival for both sexes combined varied between 81% and 100% (mean ≈91%). Breeding success in Lesser Black-backed Gulls was significantly lower than that of Herring Gulls. Lesser Black-backed Gulls experienced four consecutive breeding seasons with very low fledging rates (2006–2009) as a result of cannibalism (60–67% of all hatchlings). Chick predation was generally lower in Herring Gulls. A strong populati...