DIETARY NICHE BREADTH IN A LOCAL-COMMUNITY OF PASSERINE BIRDS, AN ANALYSIS USING PHYLOGENETIC CONTRASTS

The analysis of a local community of forest passerines (13 species) us ing phylogenetic contrasts shows a correlation between body size of bi rd species and mean prey size, minimum prey size, maximum prey size an d the size range of dietary items. This suggests that larger birds dro p small prey taxa from their prey list, because of the difficulty of c apturing very small prey, for energetic reasons or because of microhab itat usage. We find some support for the third hypothesis. Dietary nic he breadth calculated across prey taxa is not related to body size. Di etary niche breadth, however, is correlated with size-corrected measur ements of the bill and locomotor apparatus. Long and slender bills inc rease the dietary niche breadth. Thus subtle differences constrain for aging and the techniques of extracting certain prey taxa form crevices . Dietary niche breadth and foraging diversity are positively correlat ed with population density: at least locally dietary generalists occur at higher breeding densities than specialists.