Resource use by two morphologically similar insectivorous bats (Nycteris thebaica and Hipposideros caffer)

Abstract

Studies of morphologically dissimilar insectivorous bats have lead to the conclusion that morphology is the prime correlate of habitat use, and consequently of diet. This has lead to the prediction that morphologically similar bats should have similar diets. We examined the diet and morphology of two morphologically similar species, the slit-faced bat, Nycteris thebaica, and Sundevall's leaf-nosed bat, Hipposideros caffer, in the context of this prediction. Although both species foraged in the same habitat, they had distinctly different diets. The diet of N. thebaica consisted mainly of non-volant prey, primarily orthopterans and arachnids, and the diet of H. caffer, mainly of moths. Differences in wing design between the two taxa were small. The only significant difference was in aspect ratio. There were no differences in wing loading and wingtip shape ratio between the two species. The flying abilities reported for these two species are very similar, suggesting that these small differences in wing design do not translate into differences in flying ability, and cannot explain the dietary differences between these two species. On the other hand, there are marked differences in their prey detection systems which correspond to differences in their diets. H. caffer uses echolocation to detect the flapping wings of insect prey, whereas N. thebaica depends on prey-generated sounds (fluttering or scuffling) to locate its targets.