The advertisement song of Pipistrellus nathusii (Chiroptera, Vespertilionidae): a complex message containing acoustic signatures of individuals

Abstract

Males of Nathusius’ pipistrelle (Pipistrellus nathusii) are well known for their complex acoustic advertisement behaviour performed either as songflight (SF) or sedentary display (SD). We analysed phonologic, syntactic and semantic characteristics of these calls based on 2,924 acoustic records obtained from individual males repeatedly occupying 33 roosts in southern Bohemia from 1999 to 2006. Both SF and SD calls are composed of three main phonologically contrasting motifs (A, B, C) and under specific contexts often supplemented with two accessory motifs (D, E). Besides the major syntagmatic string ABC we recorded further 15 syntagms containing the main motif A and 10 syntagms without this motif. At the peak of the mating season and with the SD, the complexity of the vocalisation increases (increased variation in syntagmatic structure and syllabic composition of particular motifs, as well as in length of syntagmatic strings). The motif A corresponds to advertisement calls of congeneric species and is related to agonistic vocalisation, and B, C, D are specific for P. nathusii. B and C exhibit the largest between-individual but low within-individual variation, and their combination provides an acoustic signature of an individual and uniquely identified each particular male. Motif D corresponds to calls of mother-young communication and shows the largest syllabic variation. Motif E is a series of steep FM signals evocative of the act of landing. The message of a complete advertisement call (ABCED) could be thus: ‘(A): Pay attention, here is a P. nathusii, (B, C): I am male X, (E): land here, (D): we share a common social identity and common communication pool’. The individual characteristics of the performance of B, C, and D motifs were found to be invariant both within a season and over a series of successive years.