Bird extirpations and community dynamics in an Andean cloud forest over 100 years of land-use change.

Abstract

Long-term studies to understand biodiversity changes remain scarce- especially so in tropical mountains. Here, we document changes between 1911 and 2016 to the bird community in the cloud forest of San Antonio, a mountain ridge in the Colombian Andes. We evaluated the effects of past land-use change and assessed species vulnerability to climate disruption. Forest cover decreased from 95% to 50% by 1959 and 33 forest species were extirpated. From then to 1990, forest cover remained stable, and an additional 15 species were lost-a total of 29% of the forest community. Thereafter, forest cover increased by 26% and 17 species recolonized. The main cause of extirpations was the loss of connections to adjacent forests. Currently, of the 31 (19%) extirpated birds, 25 have ranges peripheral to San Antonio, mostly in the lowlands. Most remain regionally, but broken forest connections limit their recolonization. Other causes of extirpation are hunting, wildlife trade, and water diversion. Bird community changes include: (1) A shift from predominantly common species to a prevalence of rare ones; (2) Forest generalists replaced forest specialists that require old-growth, and (3) Functional groups such as large-body frugivores and nectarivores declined disproportionally. Moreover, we found that of the remaining 122 forest birds, 19 species are vulnerable to climate disruption, and 10 have declined in abundance. Our results inform four major topics that transcend this case study. First, we show unequivocal species losses and changes in community structure and abundance at the local scale. Second, we find that increasing habitat stops delayed extirpations and help species repopulate. Third, peripheral species to a region are more prone to extirpation when forests become fragmented. Fourth, land-use changes increase species vulnerability to climate change and threaten their persistence. We suggest measures that reverse landscape transformation can restore biodiversity and improve resistance to future threats. Article impact statement: 100 years of land-use change have produced bird extirpations and abundance declines in an Andean mountain site. This article is protected by copyright. All rights reserved.