Social Vocalizations of Big Brown Bats Vary with Behavioral Context

Abstract

Bats are among the most gregarious and vocal mammals, with some species demonstrating a diverse repertoire of syllables under a variety of behavioral contexts. Despite extensive characterization of big brown bat (Eptesicus fuscus) biosonar signals, there have been no detailed studies of adult social vocalizations. We recorded and analyzed social vocalizations and associated behaviors of captive big brown bats under four behavioral contexts: low aggression, medium aggression, high aggression, and appeasement. Even limited to these contexts, big brown bats possess a rich repertoire of social vocalizations, with 18 distinct syllable types automatically classified using a spectrogram cross-correlation procedure. For each behavioral context, we describe vocalizations in terms of syllable acoustics, temporal emission patterns, and typical syllable sequences. Emotion-related acoustic cues are evident within the call structure by context-specific syllable types or variations in the temporal emission pattern. We designed a paradigm that could evoke aggressive vocalizations while monitoring heart rate as an objective measure of internal physiological state. Changes in the magnitude and duration of elevated heart rate scaled to the level of evoked aggression, confirming the behavioral state classifications assessed by vocalizations and behavioral displays. These results reveal a complex acoustic communication system among big brown bats in which acoustic cues and call structure signal the emotional state of a caller.

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.…”

A novel coding mechanism for social vocalizations in the lateral amygdala

“…Synthetic acoustic stimuli (noise and tone bursts, 0.5 ms rise-fall time; 10 -64 ms duration) and previously recorded social vocalizations were presented at one/s. Social vocalizations consisted of 11 species-specific syllables or a combination of syllables that were previously related to aggressive (eight calls) or appeasing (three calls) behavioral contexts (Gadziola et al 2011). Duration of social vocalizations ranged from 7 to 126 ms.…”

“…For example, the sinFM syllable illustrated in Fig. 8A was observed during higher levels of aggression (Gadziola et al 2011), and syllable duration varied according to the number of cycles of frequency modulation (range: 1-5 cycles; 9 -73 ms duration). When this syllable was extended by 8 ms to include a second cycle of frequency modulation (Fig.…”

Vocal sequences suppress spiking in the bat auditory cortex while evoking concomitant steady-state local field potentials

“…The physical attributes of distress vocalizations have been intensively studied (see346161923242526272829) but, at present, comparably little is known about how distress signals are processed in the listeners’ brain, especially at the level of the auditory cortex (AC). Distress vocalizations are produced in the form of “sequences” composed of individual sound units defined as “syllables”41924253031.…”