Dietary and habitat specialization, eye size, clutch size, and aerial lifestyle predict avian fragmentation sensitivity in an Andean biodiversity hotpot

The fragmentation of tropical forests remains a major driver of avian biodiversity loss, particularly for insectivores, yet the mechanisms underlying area sensitivity remain poorly understood. Studies in lowland systems suggest that loss of food resources, changes to light microenvironments, increased nest predation, and dispersal limitation are possible mechanisms, but these are untested for montane tropical bird communities. In this study, we related avian functional traits to area sensitivity (quantified using beta estimates from a multi-species occupancy model) to test the above four hypotheses for a cloud forest bird community (both resident species and just resident insectivores) in the Colombian Western Andes. We found that species with more specialized diets and those that use the canopy and subcanopy (loss of food hypothesis), larger relative eye sizes (light microhabitat hypothesis), and larger clutch sizes (nest predation hypothesis) were significantly more area sensitive. By contrast, there was no support for the dispersal limitation hypothesis; instead, we found that insectivores with more pointed wing shapes, and more aerial lifestyles, were significantly more fragmentation sensitive. These results suggest that reduced vegetation structure, loss of late-successional plant species, and loss of epiphytic plants may reduce food availability in fragments. Similarly, the ability to tolerate higher light intensity near fragment edges, or when traversing matrix habitat, may be important for persistence in fragments and suggests that habitat configuration may be of special importance in fragmented Andean landscapes. Overall, a lack of information on foraging, movement, and breeding ecology complicates avian conservation in the Andes.