Highway Noise Worsens the Edge Effect on Bird Richness in Tropical Forests

Anthropogenic noise represents a major threat to various taxonomic groups of fauna, especially birds, as they primarily use sound communication. Associated with the edge effect caused by highways, noise has a negative impact on birds. In this context, the aim of this study was to assess the impact of noise on birds in an area intersected by a highway in a tropical forest in Brazil. Eight transects were built, with points perpendicular to the edges (10, 200, 400, 600, and 800 m), in three areas: highway, pasture, and control (named Forest). At each point, the maximum noise level and bird richness were recorded every 2 months for a year. Five generalised linear mixed models were built to assess whether bird richness was influenced by edge type (highway and pasture), noise, and distance from the edge. The noise was most intense in the road environment and decreased as one moved perpendicularly away from the edge of the road and the pasture. Bird richness was highest in the control area and lowest on the highway, increasing linearly with distance from the edge of the highway and pasture, and decreasing with noise level on both the highway and pasture. Bird richness was better explained by distance from the highway and pasture than by noise, with both factors having a stronger impact at the highway edge than at the pasture edge. Our results suggest (i) that the noise levels of the highway aggravate the edge effect and influence the variation in species richness, (ii) that species from forest environments move away from the area intercepted by the highway.