SOCIAL-STRUCTURE OF 3 SYMPATRIC BAT SPECIES (VESPERTILIONIDAE)

The social structure of three sympatric bat species occupying bat boxe s in woodland in southern England was studied: Pipistrellus pipistrell us (pipistrelle), Plecotus auritus (brown long-eared bat) and Myotis n attereri (Natterer's bat). Before parturition, P. pipistrellus populat ions were heavily skewed towards solitary males. After parturition, th e sex ratio was closer to unity. Recaptures of marked bats suggested t hat after parturition a resident male population of P. pipistrellus is invaded by a transient female population. The sex ratios of populatio ns of P. auritus and M. nattereri were very close to unity, both pre- and post-parturition. The numbers of recaptures of individual bats wer e similar for both sexes in P. auritus and slightly higher for females in M. nattereri. In the mating season (August-October), solitary male P. pipistrellus were found with small groups (1-9) of females. In con trast, in both P. auritus and M. nattereri, mixed sex groups were foun d pre-and post-parturition, and roosting groups in the mating season c ontained up to 20 females and up to 10 males. The stability of female groups in P. auritus appeared to be higher than M. nattereri and P. pi pistrellus as known females were found together more frequently. These patterns are discussed with reference to the possible differences in foraging and social behaviour.