Habitat selection and its effect on reproductive output in the herring gull in Newfoundland.

Abstract

Larus argentatus nesting in 3 different habitats (designated puffin, rocky, and meadow) were compared with regard to several reproductive parameters. More pairs nested in rocky habitat, fewer pairs in puffin habitat, than expected from a random distribution. In 1977, a year of low food availability, pairs in rocky habitat laid and hatched eggs earlier than in the other habitats. In 1978, when food was more abundant, gulls in rocky habitat laid heavier eggs. In both 1977 and 1978, chicks from rocky habitat grew at the fastest rate and were heavier than chicks in the other habitats. Female gulls in rocky habitat were capable of producing significantly more eggs than their counterparts in meadow and puffin habitats. Despite the better condition of gulls in rocky habitat, however, herring gull pairs in puffin habitat fledged as many chicks per nest as pairs in rocky habitat in 1977 and 1978. Gulls in meadow habitat fledged the fewest chicks per nest. Within habitats, chick survival was strongly correlated with early laying dates and high rates of growth, but there was also a large residual effect which was probably due to differences in the habitats. These differences are probably due to crowding and socially induced mortality in rocky habitat, and to the presence of predatory great black-backed gulls L. marinus in meadow habitat. Increasing density in a preferred habitat can create a situation whereby fitness may actually be greater in a less-preferred habitat.-from Author