Unusual social calls of Nathusius' pipistrelle (Vespertilionidae, Chiroptera) recorded outside the mating season
Abstrakt
The advertisement calls of Nathusius' pipistrelle (Pipistrellus nathusii) show an unified structure: three main motifs which can be supplemented with additional two motifs especially during mating season. In May and June, a continuous social vocalization of quite unusual structure and composition was recorded apart from these standard calls.
Most of these calls were designed in a long "wavy line" pattern with the peak frequency of 14-36 kHz, and were accompanied by standard or modified echolocation calls. In one case we succeeded to supplement the acoustic records with a complete record of behavioural details: two bats slowly flew and followed one another in a circular path in front of the roost, where they repeatedly performed false landings, and during approaching one of them emitted the unusual social calls.
This behaviour lasted for about 40% of the whole-night activity. The possible meaning is discussed.