Social calls of Myotis nattereri during swarming: Call structure mirrors the different behavioral context.

Philipp Schmidbauer,Annette Denzinger,Jon T Sakata

doi:10.1371/journal.pone.0221792

Abstract

Swarming is a characteristic behavior of bats that occurs in different social contexts. We studied the swarming behavior of Myotis nattereri at a maternity colony and at an autumn swarming site in South-West Germany by using synchronized sound and video recordings. Swarming was always associated with social vocalizations consisting of four frequently occurring call types. Call type A was a short call with a broadband steep-shallow-steep downward frequency modulation. Call type B consisted of two elements beginning with a broadband upward hooked element followed by a steep frequency modulated element. Call type C showed a characteristic rapid downward-upward-downward frequency modulation. Call type D was a long sinusoidal trill-like call with high variability in signal structure. All call types were recorded at the maternity colony, as well as at the autumn swarming site, but the incidence of each call type differed distinctly between the study sites. At the maternity roost, type A calls were most commonly produced. We found evidence for an individual signature in this call type and suggest that this social call has the function of a contact call in Natterer’s bats. At the autumn swarming site, type D calls were the most common social calls; in contrast, this call type was recorded only twice at the maternity roost. The occurrence of trills mainly at the autumn swarming site and their high variability suggests that trills function as male advertisement calls in M. nattereri.

Highlights

Many bat species live in groups with complex social structures where communication with conspecifics plays a crucial role [1]
We focused on M. nattereri, which is widespread in Europe and one of the most common species at autumn swarming sites
[EXSCINDED]Social calls of Myotis nattereri during swarming swarmed in small groups of two to four individuals for a few minutes before they entered the roost in quick succession

Summary

Introduction

Many bat species live in groups with complex social structures where communication with conspecifics plays a crucial role [1]. Like in many other animal taxa, communication in bats can be mediated by acoustic, olfactory, visual, and tactile signals [2]. Acoustic communication is the most suitable modality for social communication for highly mobile, nocturnal animals like bats [2, 3]. Vocalizations are independent from illumination and transfer information over long distances. As an adaptation to long distance transmission social calls are usually lower in frequency and show a higher complexity than echolocation calls [3,4,5]. Social calls that are produced by bats during flight can be differentiated into three groups based on their function and signal structure.

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