Responses of understory rain forest birds to road edges in central Amazonia

Abstract

In the lowland tropical rain forest of central Amazonia, I investigated the responses of understory bird communities to forest edges bordering a narrow (<40 m width), unpaved road. From 3681 mist-net captures, bird abundance and composition were examined at three distances (10, 70, and 130 m) from forest edge. The degree to which regrowth vegetation along forest borders reduced edge effects was also assessed by contrasting bird communities near roads with varying levels of regrowth. Forests near road margins had reduced canopy cover and height and higher numbers of fallen trees than did forest interiors. Bird communities near forest edges also differed markedly from those in forest interiors. Total bird captures and captures of insectivores increased with distance from edge, whereas captures of frugivores and nectarivores did not vary significantly. Mature regrowth on edges significantly increased the captures of insectivores. When insectivorous birds were divided into feeding guilds, birds in six of eight guilds showed significant responses to distance from edge; five of these had fewer captures near road margins whereas one guild (edge/gap specialists) had higher captures. For most guilds, significant alterations in abundance and species composition were evident within 10-70 m of road margins. My results suggest that the majority of Amazonian understory birds respond negatively to artificial edges created by a narrow, unpaved road. Forest regrowth along road margins alleviated negative edge effects for only a limited subset of forest-dependent species.