Barbastelle bats (Barbastella spp.) specialize in the predation of moths: Implications for foraging tactics and conservation

The diet of barbastelle bats, Barbastella (b.) barbastellus and B. (b.) leucomelas, captured respectively, in the Swiss Alps and in the Kirghiz Tien Shian and Pamir mountains (central Asia) was investigated through faecal analysis. Location of hunting habitats and data on foraging behaviour of Swiss barbastelle bats were obtained from radiotracking. In either area, ca. 99% of prey by volume consisted of Lepidoptera. The regular occurrence of one small arctiid species in the diet of Swiss barbastelles, as well as the predominance (84%) of tympanate moths among the Lepidoptera sampled at foraging sites suggest that B. barbastellus could prey to a large extent on smaller tympanate moths. Observations of foraging bats showed that, in the study area, barbastelles behaved as typical aerial-hawking bat species, although they hunted exclusively just above the forest canopy. This aerial-hawking bat species has seemingly evolved a peculiar foraging technique to overcome the defence system of its probable tympanate prey. The diet of Barbastella appears one of the narrowest among Palaearctic bats. Such a specialization in foraging habits probably points to a higher vulnerability,of this species, as compared to other more flexible aerial-hawking bats, to negative changes in the abundance of moth populations. This could explain its current rarity throughout most of Europe.