Responses of avian assemblages to a natural edge in a Chaco semiarid forest in Argentina

We assessed differences in breeding bird assemblages and vegetation structure between a natural forest edge and the adjacent forest interior in an old-growth Chaco forest of Argentina. The edge had a dense cover of thin stems at low heights and high species richness of woody plants, whereas the interior had high canopy cover, high tree density, high density of thick stems, and a more heterogeneous vertical profile. We used mist-net and point-count surveys to sample bird assemblages, capturing 374 birds during 3,553 net hours and detecting 826 individuals during point counts. Overall, we recorded a total of 74 bird species. Bird species richness and bird abundance appeared to be higher in the edge, although differences between habitats were not entirely consistent for mist-net and point-count data. Several early successional bird species were closely associated with edge, and other species occurred exclusively in the interior of the forest. At the guild level, frugivores, terrestrial granivores, arboreal granivores, terrestrial insectivores, and long-flight insect-hunters were more abundant at the edge than in the interior, whereas the reverse was true for bark insectivores and short-flight insectivores. Our results indicate that edge and interior bird assemblages are different. The distribution of birds between these habitats appeared to reflect constraints on habitat use imposed by vegetation structure, and also could be related to differential distribution of food resources, especially fruit.