Habitat Selection and Reproductive Performance of Food-Stressed Herring Gulls

Abstract

Recently increasing populations of Herring Gulls (Larus urgentutus) in Newfoundland were food stressed by the late arrival of capelin (M&lotus villosus), the main prey fed to chicks, to inshore waters in 1992-1993. Our purpose was to determine how this food shortage would affect inter-habitat differences in breeding performance on Great Island, Newfoundland. A previous study comparing breeding success among rocky, puffin, and meadow habitats identified rocky as the preferred habitat and provided equivocal support for an ideal-free distribution. We predicted that food stress would accentuate differences between birds assorted by competitive ability and result in higher breeding success for pairs nesting in preferred habitat, as predicted by ideal-despotic and phenotype-limited ideal-free habitat selection models. Responses to food shortage included later hatching, smaller clutches, and reduced hatching and fledging success. Arrival of capelin four weeks after hatching began resulted in an advantage for late-hatched chicks and a reversal of the typical positive relationship between breeding success and large, early laid clutches. Higher and buffered nest density, and a greater proportion of pairs laying eggs indicated that rocky was still the preferred habitat. However, breeding success was as high or, more frequently, higher in other habitats in this and previous studies, contrary to predictions of habitat selection models. That rocky was the original nesting habitat on Great Island suggests an ultimate, probably genetic, component to habitat selection by Herring Gulls, which, in the absence of consistent trends in habitat suitability, may have maintained the preference for rocky habitat.