Habitat fragmentation causes drastic changes in the biota and it is crucial to understand these modifications to mitigate its consequences. While studies on Neotropical bats have mainly targeted phyllostomid bats, impacts of fragmentation on the equally important aerial insectivores remain largely unexplored. We studied species richness, composition, count abundance and feeding activity of aerial insectivorous bats in a system of land-bridge islands in Panama with acoustic sampling. We predicted negative effects of fragmentation on forest species while bats foraging in open space should remain essentially unaffected. Rarefaction analyses indicated higher species richness for islands than mainland sites. For forest species, multivariate analyses suggested compositional differences between sites due to effects of isolation, area and vegetation structure. Contrary to our expectations, count abundance of forest species was similar across site categories. Feeding activity, however, was curtailed on far islands compared to near islands. As expected, bats hunting in open space did not reveal negative responses to fragmentation. Interestingly, they even displayed higher abundance counts on far and small islands. On the species level, two forest bats responded negatively to size reduction or site isolation, respectively, while a forest bat and a bat hunting in open space were more abundant on islands, irrespectively of island isolation or size. Our findings suggest that small forest remnants are of considerable conservation value as many aerial insectivores intensively use them. Hence high conservation priority should be given to retain or re-establish a high degree of forest integrity and low levels of isolation.
