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      Social Vocalizations of Big Brown Bats Vary with Behavioral Context

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          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.

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          Most cited references27

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          The acoustic structure of suricates' alarm calls varies with predator type and the level of response urgency.

          The variation in the acoustic structure of alarm calls appears to convey information about the level of response urgency in some species, while in others it seems to denote the type of predator. While theoretical models and studies on species with functionally referential calls have emphasized that any animal signal considered to have an external referent also includes motivational content, to our knowledge, no empirical study has been able to show this. In this paper, I present an example of a graded alarm call system that combines referential information and also information on the level of urgency. Acoustically different alarm calls in the social mongoose Suricata suricatta are given in response to different predator types, but their call structure also varies depending on the level of urgency. Low urgency calls tend to be harmonic across all predator types, while high urgency calls are noisier. There was less evidence for consistency in the acoustic parameters assigned to particular predator types across different levels of urgency. This suggests that, while suricates convey information about the level of urgency along a general rule, the referential information about each category of predator type is not encoded in an obvious way.
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            Echolocation behavior of big brown bats, Eptesicus fuscus, in the field and the laboratory.

            Echolocation signals were recorded from big brown bats, Eptesicus fuscus, flying in the field and the laboratory. In open field areas the interpulse intervals (IPI) of search signals were either around 134 ms or twice that value, 270 ms. At long IPI's the signals were of long duration (14 to 18-20 ms), narrow bandwidth, and low frequency, sweeping down to a minimum frequency (Fmin) of 22-25 kHz. At short IPI's the signals were shorter (6-13 ms), of higher frequency, and broader bandwidth. In wooded areas only short (6-11 ms) relatively broadband search signals were emitted at a higher rate (avg. IPI= 122 ms) with higher Fmin (27-30 kHz). In the laboratory the IPI was even shorter (88 ms), the duration was 3-5 ms, and the Fmin 30- 35 kHz, resembling approach phase signals of field recordings. Excluding terminal phase signals, all signals from all areas showed a negative correlation between signal duration and Fmin, i.e., the shorter the signal, the higher was Fmin. This correlation was reversed in the terminal phase of insect capture sequences, where Fmin decreased with decreasing signal duration. Overall, the signals recorded in the field were longer, with longer IPI's and greater variability in bandwidth than signals recorded in the laboratory.
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              Echolocation and pursuit of prey by bats.

              Echolocating bats use different information-gathering strategies for hunting prey in open, uncluttered environments, in relatively open environments with some obstacles, and in densely cluttered environments. These situations differ in the extent to which individual targets such as flying insects can be detected as isolated objects or must be separated perceptually from backgrounds. Echolocating bats also differ in whether they use high-resolution, multidimensional images of targets or concentrate specifically on one particular target dimension, such as movement, to detect prey.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                1932-6203
                2012
                7 September 2012
                : 7
                : 9
                : e44550
                Affiliations
                [1 ]Department of Anatomy and Neurobiology, Northeast Ohio Medical University, Rootstown, Ohio, United States of America
                [2 ]School of Biomedical Sciences, Kent State University, Kent, Ohio, United States of America
                [3 ]Department of Psychology, Neuroscience & Behaviour, McMaster University, Hamilton, Ontario, Canada
                University of Southern California, United States of America
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Conceived and designed the experiments: MAG JJW. Performed the experiments: MAG. Analyzed the data: MAG JMSG JJW. Contributed reagents/materials/analysis tools: PAF JJW. Wrote the paper: MAG JMSG PAF JJW.

                Article
                PONE-D-12-07013
                10.1371/journal.pone.0044550
                3436781
                22970247
                d2a897c1-425e-4b66-91e9-17de4f4729f4
                Copyright @ 2012

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 7 March 2012
                : 6 August 2012
                Page count
                Pages: 15
                Funding
                This work was supported by the National Institute on Deafness and Other Communication Disorders grant R01 DC00937-20 and supplements 18S1 and 19S1 to J.J.W., and by a Discovery Grant from the Natural Sciences and Engineering Research Council of Canada to P.A.F. The McMaster Bat Lab was supported by infrastructure grants from the Canada Foundation for Innovation and the Ontario Innovation Trust. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Biology
                Model Organisms
                Animal Models
                Neuroscience
                Sensory Systems
                Auditory System
                Behavioral Neuroscience
                Neuroethology
                Sensory Perception
                Zoology
                Animal Behavior

                Uncategorized
                Uncategorized

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