DOI: 10.5061/dryad.2z34tmpnb
title: Response of Avian communities to edges of tropical montane forests: Implications for the future of endemic habitat specialists

description: 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.
description: These data come from audio-visual surveys (point counts)
 conducted in May-July (the avian breeding season) of 2006 from 1100-1800 m
 elevation, at 110 points, including 77 points located in forest interior
 and 33 points near forest edges. Points were separated by &gt;200 m to
 avoid double counting individuals across points, and were distributed
 across a moisture gradient defined by the distance of points to the
 continental divide. Edge points were placed inside the forest 50 m from a
 boundary with a clearing to keep the sampled area within forest.
 Interior points were placed &gt;200 m from a boundary. All birds seen
 or heard in 10 min within a 50 m radius by two observers were recorded
 with the estimated distance of detection. Counts were repeated at each
 point weekly, a total of five times over the season (see published article
 for further details). We used the maximum number of simultaneously
 detected conspecifics per point across all visits for each species’
 abundance value at each point, and created a site by species matrix using
 these values. The dataset provided shows the site by
 species matrix, with sites (point labels="SITE") as rows, and
 associated point data (distance of point from the continental divide in
 meters = "DTD"; elevation of point in m.a.s.l. =
 "ELEV"; categorical zone of distance from the continental divide
 = "DTD_ZONE"; categorical variable labeling each site as a
 forest dge or interior point = "INT-EDG"; zone-habitat as a
 merged column of DTD_ZONE and INT-EDG = "ZONE_HAB") and the
 remaining columns as species (shown by each species' letter
 code). Values in the data matrix show the maximum number of simultaneously
 detected individuals of a species at a point over the five visits to the
 site. A table of letter codes of species corresponding to the columns of
 this data matrix can be found in Table A2 of published Supplementary
 Material.