Differences in songflight calls and social calls between two phonic types of the vespertilionid bat Pipistrellus pipistrellus

Abstract

The pipistrelle (Pipistrellus pipistrellus) occurs as two phonic types in Britain, its echolocation calls falling into two distinct frequency bands, with mean frequencies of maximum energy at 55 kHz and 46 kHz. These are termed the 55 kHz and 45 kHz phonic types here for simplicity. Songflight calls produced by males in the mating season, probably to attract females, differed between the two phonic types in the number of components in the calls and the call parameters measured. Songflight calls of the 55 kHz phonic type, which generally consisted of three components, were of higher frequencies than those of the 45 kHz phonic type, usually of four components. There were also significant differences in call parameters among individuals. A discriminant analysis of songflight calls classified 100% of individuals to the correct phonic type. The relationships between echolocation call frequency and songflight call frequency differed significantly between phonic types. Social calls produced during flight also differed between phonic types, in the number of components and call parameters measured. Social calls were compared to songflight calls of each phonic type. Social calls of the 55 kHz phonic type did not differ significantly from songflight calls; there were small but significant differences between the two types of calls of the 45 kHz phonic type. The study provides support for the hypothesis that the phonic types should be treated as sibling species. If songflight calls are used for mate choice, the differences may allow reproductive isolation between the two phonic types. The functions of songflight calls and social calls need to be investigated through experimental studies to explain the implications of the differences between phonic types.