A flexible communicator: Social call repertoire of Savi’s pipistrelle, Hypsugo savii

Bat social calls are specifically tailored for communication and play different roles according to their structure. Their structure is stereotyped and species-specific so they may aid acoustic identification of bats. To provide the first quantitative description of social call repertoire of Hypsugo savii and offer a way to identify this bat in free flight we made audio recordings in four areas of Central and Southern Italy in summers 2011–2015. We identified single and multiple-component social calls and categorized them into five structure types. Within each structure type, call frequency and / or duration differed between single and multiple-component calls, the latter being shorter and showing higher frequencies. In multiple-component calls both the number of syllables and the way they were associated were highly variable, making it difficult to recognize patterns. Some motifs, however, showed the same first component type and final sequence. We also recorded trill-like calls and two complex sequences of multiple-component social calls (songs) lacking repeated motifs. The complex association of syllables, the rarity of recurrent motifs and the significant structural flexibility suggest that social calls serve a range of scopes and that they might convey acoustic signatures and other individual-specific features.