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.
Highlights
Acoustic communication plays a primary role in social interactions among many species of bats
We describe the probability of different syllable types occurring, their acoustic structures, temporal emission patterns, and the probability of syllable transitions
This study characterized adult social vocalizations of big brown bats emitted under four behavioral contexts: low aggression, medium aggression, high aggression, and appeasement
Summary
Acoustic communication plays a primary role in social interactions among many species of bats. Complex social vocalizations are learned in some species of bats [16,17,18,19], including babbling behavior in bat juveniles [20]. Such acoustic phenomena are widespread among songbirds, the complexity of acoustic communication systems observed in bats are exceptional in the mammalian world, making bats an important model for studies of acoustic communication. There is recent evidence that greater false vampire bats (Megaderma lyra) make systematic changes to the call structure, such as the number and repetition rate of syllables, according to the intensity level of agonistic interactions [9], and such changes provide prosodic cues that listeners may evaluate [29]. Important questions still surround the accuracy with which the acoustic signals reflect the internal affective state of the caller and what influence these sounds have on a listener
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