Effects of forest disturbance and habitat loss on avian communities in a Neotropical biodiversity hotspot

Regenerating forests are increasingly ubiquitous in tropical landscapes. They hold great conservation potential and there is demand for assessments of their biodiversity value. Forest disturbance and forest loss often occur together, yet few studies attempt to disentangle their separate effects on biological communities. In the Ecuadorian Chocó, a biodiversity hotspot, we sampled understory birds in patches with increasing levels of disturbance (old-growth, selectively-logged, and secondary forests) within contiguous forest and in fragments. Species richness increased with disturbance but decreased with habitat loss, with a 75% reduction in endemic and threatened species in fragments compared to contiguous forest. This reduction in richness was most pronounced in secondary forest fragments, suggesting that disturbance and habitat loss interact synergistically to maximally reduce avian biodiversity. Species composition was strongly affected by habitat loss and, to a lesser extent, disturbance, with forest fragments and secondary forests presenting distinct communities dominated by generalists with medium-to-low sensitivity to anthropogenic disturbance and reduced proportions of endemics and endangered species. Capture rates also decreased (non-significantly) with habitat loss, and the relative abundance of dietary guilds varied in response to both habitat loss and disturbance. Our study shows that regenerating patches surrounded by contiguous forest can sustain high biodiversity levels and, when past habitat disturbance is mild, present similar communities to old-growth forests. In contrast, forest loss caused reductions in richness (especially in more disturbed patches), profound changes in community composition, and loss of species of conservation concern. These results underscore the importance of considering landscape context when evaluating the conservation value of disturbed forests.