Repertoire and possible functions of social calls in foraging big brown bats (Eptesicus fuscus).

Abstract

While the echolocation calls of big brown bats (Eptesicus fuscus) have been studied extensively, this species’ communicative vocalizations have received little attention. Calls were recorded from pairs of bats flying in a laboratory flight room in a foraging context. Pairs consisted of naive bats flown with individuals that were either experienced about how to take a tethered insect or naive or of two experienced bats flying together. This situation elicited a variety of vocalizations with properties different from typical E. fuscus echolocation calls. Seven different call shapes that occurred only when two bats were present were identified and categorized. These included chirp-like calls, rising frequency calls, calls that were longer than 20 ms in duration, and series of ultrasonic, chirp-like calls (or “songs”) produced only by male bats and displaying individual variation. Some call types were only recorded when a juvenile was present or very rarely in adult-only pairs. Using high-speed video data collected in synchrony with the audio recordings, the contexts and possible functions of various calls are evaluated. The rate at which different call types were recorded with regard to bats’ knowledge of the foraging task and the age and sex of bats flown together is also considered.