Competition for food by expanding pipistrelle bat populations (Pipistrellus pipistrellus) might contribute to the decline of lesser horseshoe bats (Rhinolophus hipposideros)

The bat species Rhinolophus hipposideros has undergone a dramatic decline throughout much of western Europe from the 1960s. The mechanisms responsible for this phenomenon have not been conclusively identified. At the same time, some populations of Pipistrellus pipistrellus have increased substantially, possibly as a consequence of foraging upon insects attracted by street lamps. To evaluate whether there might be some ecological link between the opposite demographic trends observed in the two species, we compared the diets of two sympatric populations of R. hipposideros and P. pipistrellus in south-west Switzerland. The two bat species fed upon the same categories of prey, mainly moths and Diptera, and we were not able to recognize interspecific differences in diet composition in spring when resources were most likely to be limiting. Although using different foraging strategies, both species may visit the same or adjacent feeding grounds, therefore potentially competing for the same populations of prey. Although conclusive evidence is still needed, bat conservation policy should pay more attention to this possibility. (C) 2000 Elsevier Science Ltd. All rights reserved.