Social calls of flying big brown bats (Eptesicus fuscus)

Abstract

Vocalizations serving a variety of social functions have been reported in many bat species (Order Chiroptera). While echolocation by big brown bats (Eptesicus fuscus) has been the subject of extensive study, calls used by this species for communication have received comparatively little research attention. Here, we report on a rich repertoire of vocalizations produced by big brown bats in a large flight room equipped with synchronized high speed stereo video and audio recording equipment. Bats were studied individually and in pairs, while sex, age, and experience with a novel foraging task were varied. We used discriminant function analysis (DFA) to classify six different vocalizations that were recorded when two bats were present. Contingency table analyses revealed a higher prevalence of social calls when males were present, and some call types varied in frequency of emission based on trial type or bat age. Bats flew closer together around the time some social calls were emitted, indicating that communicative calls may be selectively produced when conspecifics fly near one another. These findings are the first reports of social calls from flying big brown bats and provide insight into the function of communicative vocalizations emitted by this species.

Big brown bats (Eptesicus fuscus) emit intense search calls and fly in stereotyped flight paths as they forage in the wild

“…The recordings we made included search, approach and terminal phase calls (Griffin et al, 1960;Surlykke and Moss, 2000), which confirmed that the bats were foraging and not commuting from one site to another, corroborating a previous report of this area as a hunting field for E. fuscus (Surlykke and Moss, 2000). We did not record any calls that could be characterized as E. fuscus social calls (Gadziola et al, 2012;Wright et al, 2013Wright et al, , 2014. The AMSL of the echolocation calls recorded was 133-138 dB (RMS re.…”

Social Calls Predict Foraging Success in Big Brown Bats

“…1). Using a combination of visual and auditory examination confirmed with results from a discriminant function analysis (DFA) to distinguish this call type from others [5], we identified FMB in 91 of the 322 two-bat recordings with at least one bat skilled at capturing the prey item and in none of the 603 single-bat recordings in this study. Table S3 summarizes the number of trials in each context and the number of trials of each type containing one or more FMB.…”

“…Synchronized high-speed video and audio recordings were acquired and digitally stored, allowing for careful analysis of call features and reconstruction of bat three-dimensional (3D) flight paths and positions. We examined bats’ behavior surrounding the frequency-modulated bout (FMB), a sequence of three to four calls, longer in duration and lower in frequency than typical big brown bat echolocation pulses [5; Fig. 1].…”

“…A variety of birds and mammals emit food-associated calls that inform, attract, or repel conspecifics [e.g., 1]. Big brown bats ( Eptesicus fuscus ) are insectivorous aerial hawkers that may forage near conspecifics and are known to emit social calls [e.g., 2, 3, 4, 5]. Calls recorded in a foraging setting might attract [e.g., 6] or repel conspecifics [7] and could denote territoriality or food-claiming.…”

“…Calls recorded in a foraging setting might attract [e.g., 6] or repel conspecifics [7] and could denote territoriality or food-claiming. Here, we provide evidence that a social call emitted only by male bats, exclusively in a foraging context [5], the “frequency-modulated bout” (FMB), is used to claim food and is individually distinct. Bats were studied individually and in pairs in a flight room equipped with synchronized high-speed stereo video and audio recording equipment, while sex and experience with a foraging task were experimentally manipulated.…”