Foraging Niches and the Structure of Forest Bird Communities in Contrasting Montane Habitats

The foraging niche patterns of woodpeckers and insectivorous passerines in two montane forests in New Hampshire were characterized and compared in separate and joint multivariate analyses. Comparisons of these two communities occurring in contrasting environments help to identify and assess the relative importance of the factors determining their species compositions and niche structures. The most important of these are shown to be the interrelated effects of climate, habitat physiognomy, competitive interactions, food resource base, wintering habits, and biogeographic origin of the avifaunas. Subalpine birds had lower and more variable population densities, plus lower niche diversity but greater niche overlap than birds of northern hardwoods. Niche ordinations showed that canopy height and foraging substrate were important gradients in the organization of both communities. We conclude that the patterns of bird community structure in these particular habitats are responses to diverse evolutionary and ecological events that determine individual species' patterns of habitat selection and resource exploitation.