Bats and the loss of tree canopy in African woodlands

We studied the activity patterns, abundance, diversity, and diets of bats, along with the abundance of nocturnal volant insects, at 30 sites in Miombo woodland in northern Zimbabwe. The woodland at 50% of the sites had been disturbed by high elephant densities to the extent that the free canopy was greatly reduced The tree canopy was intact at the other sites. Intact and impacted sites differed significantly in tree (>3 m tall; >15 cm basal diameter) and shrub (1-3 m tall; (1 m tall) diversity and cover. At each site we used ultraviolet lights to sample insects and mist nets and bat detectors to sample bats. To assess their diets we collected and analyzed feces from captured bats. We caught 343 bats representing the families Pteropodidae (1 species), Vespertilionidae (11 species), and Molossidae (3 species). The molossids and vespertilionids are all aerial feeders taking airborne insects. Bat species richness, abundance, and activity were greater at intact than at impacted sites, but these differences were statistically significant only at adjacent sites (<5 km apart) not at more distant intact and impacted sites (>20 km apart). At the adjacent sites we caught a significantly greater proportion of small (<10 g) bats at intact than at impacted sites. These data and a significantly greater proportion of Scotophilus species (>10 g) caught during the early evening at intact than at impacted sites suggested that the removal of canopy trees affected roost availability for the bats. Although larger species may have commuted between intact and impacted sites, smaller species did not. In contrast the availability of prey did not appear to have been significantly affected by the removal of the canopy trees, as indicated by the light-trap catches of insects and the bats' diets Most bats ate mainly beetles and moths, the most abundant insects sampled at the ultraviolet lights. Our findings suggest that aerial-feeding bats such as vespertilionids and molossids do not appear to be useful indicators of disturbance in this habitat, even in the face of significant loss of tree canopy.