Response of avian communities to edges of tropical montane forests: Implications for the future of endemic habitat specialists

Tropical montane landscapes harbor diverse flora and fauna, and many species there are ecological specialists with narrow elevational distributions, limited geographic ranges, and small global populations. Along elevational gradients, environmental conditions and community composition change dramatically over small spatial scales. As forests are disturbed and edges formed with modified habitat, natural communities could be affected differently across elevations by the many physical and biotic changes at edges. We asked whether forest edges produced altered patterns of avian species composition along a cloud forest - dry forest gradient on the Pacific slope of the Tilarán mountains in Monteverde, Costa Rica. A strong moisture gradient produces cloud forests near the ridgetops, with a concentration of species endemic to the Costa Rica – Panama highlands that are habitat specialists. We conducted 552 point counts across 110 locations from 1100 to 1800 m elevation, yielding 6586 detections of 115 species in 10 km2 of montane forest. We analyzed differences in species composition and single-species abundances between interior and near-edge forest habitats for species grouped by geographic range size. Species composition changed markedly from forest edge to interior in cloud forest habitats, but not in drier forests downslope. Endemic species, especially in cloud forest, were detected less frequently in mature forest near edges than in mature forest interior, and this difference was more pronounced than for cosmopolitan species. On tropical mountainsides, we can expect habitat-specialist endemic species to be more sensitive to further habitat modification. This sensitivity could limit the resilience of tropical bird communities.