Habitat Selection and Its Effect on Reproductive Output in the Herring Gull in Newfoundland

Abstract

The breeding biology of the Herring Gull (Larus argentatus) was studied on Great Island, Newfoundland for part of the 1976 breeding season, and for two succeeding complete breeding seasons (1977 and 1978). Gulls nesting in three different habitats (designated puffin, rocky, and meadow) were compared with regard to several reproductive parameters. More pairs were found to nest in rocky habitat, and fewer pairs were found to nest in puffin habitat, than would be expected from a random distribution. In 1977, a year of low food availability, pairs in rocky habitat laid and hatched eggs significantly earlier than in the other two habitats. In 1978, when food was more abundant, gulls in rocky habitat laid heavier eggs than their counterparts in the other habitats. In both 1977 and 1978, chicks from rocky habitat grew at the fastest rate and were heavier than chicks in the other habitats. Finally, results of an experiment to test the egg-production capacity of females demonstrated that female gulls in rocky habitat were capable of producing significantly more eggs than their counterparts in meadow and puffin habitats. Despite the apparently 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, and even fledged more chicks in 1976. In all 3 yr of study, 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. However, 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 in meadow habitat. The results support the theoretical models for habitat selection and dispersion developed by Fretwell and Lucas (1970), which suggest that increasing density in a preferred habitat can create a situation whereby fitness may actually be greater in a less-preferred habitat.