High frequency social calls indicate food source defense in foraging Common pipistrelle bats

Annette Denzinger,Simone Götze,Hans-Ulrich Schnitzler

doi:10.1038/s41598-020-62743-z

Abstract

Social calls have the function to coordinate the behavior of animals. In the presence of conspecifics foraging Common pipistrelle bats (P. pipistrellus) emitted, in addition to typical echolocation signals, two types of social calls: complex social calls and an as-of-yet undescribed, short, frequency-modulated call type with high terminal frequency, which we term “high frequency social call”. By recording the flight and acoustic behavior of free flying pairs of foraging P. pipistrellus with an array of four microphones we were able to determine their three-dimensional flight paths and attribute emitted calls to particular behavioral situations. Complex social calls were emitted at further inter-individual distances and at large bearing angles to conspecifics, whereas high frequency social calls were produced at significantly shorter distances and at smaller bearing angles. These calls were associated with chasings and the eviction of the intruder. We assume that the emission of both types of social calls by foraging bats reflects a two-stage-process of the occupation and defense of a food patch. Common pipistrelle bats use complex social calls to claim a food patch and switch to agonistic behaviors, including chasings and high frequency social call emissions, when they defend their foraging territory against an intruder.

Highlights

Social calls have the function to coordinate the behavior of animals
Our sound recordings with an array of four microphones allowed the reconstruction of the three-dimensional flight paths of foraging pipistrelles flying either alone or together with conspecifics and the calculation of the bats’ positions at the emission of the recorded sounds
With this method we are able to attribute the emission of specific calls to particular behavioral situations

Summary

Introduction

Social calls have the function to coordinate the behavior of animals. In the presence of conspecifics foraging Common pipistrelle bats (P. pipistrellus) emitted, in addition to typical echolocation signals, two types of social calls: complex social calls and an as-of-yet undescribed, short, frequency-modulated call type with high terminal frequency, which we term “high frequency social call”. Common pipistrelle bats use complex social calls to claim a food patch and switch to agonistic behaviors, including chasings and high frequency social call emissions, when they defend their foraging territory against an intruder. In contrast to types A and B, which are emitted only by stationary bats at the roost, Types C and D are produced by individuals during flight Of these flight calls, Type C is a single-element contact signal used in mother-infant interactions, whereas Type D consists of 2–5 multi-harmonic frequency-modulated syllables, a call that is referred to as ‘complex social call’[2,16]. In the current study we recorded signals from Pipistrellus pipistrellus which were different from the species’ echolocation signals and their known social calls These were sweeps of short duration and high terminal frequency which were emitted in striking temporal proximity to Type 1 calls. We preliminary termed these ‘Type 2 calls’ and sought to understand the purpose of their emission

Methods

Results

Conclusion