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

Studies of morphologically dissimilar insectivorous bats have lead to the c onclusion that morphology is the prime correlate of habitat use, and conseq uently of diet. This has lead to the prediction that morphologically simila r bats should have similar diets. We examined the diet and morphology of tw o morphologically similar species, the slit-faced bat, Nycteris thebaica, a nd Sundevall's leaf-nosed bat, Hipposideros caffer, in the context of this prediction. Although both species foraged in the same habitat, they had dis tinctly different diets. The diet of N. thebaica consisted mainly of non-vo lant prey, primarily orthopterans and arachnids, and the diet of H. caffer, mainly of moths. Differences in wing design between the two taxa were smal l. The only significant difference was in aspect ratio. There were no diffe rences in wing loading and wingtip shape ratio between the two species. The flying abilities reported for these two species are very similar, suggesti ng that these small differences in wing design do not translate into differ ences in flying ability, and cannot explain the dietary differences between these two species. On the other hand, there are marked differences in thei r prey detection systems which correspond to differences in their diets. H. caffer uses echolocation to detect the flapping wings of insect prey, wher eas N. thebaica depends on prey-generated sounds (fiuttering or scuffling) to locate its targets.