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Journal of the Acoustical Society of America / Volume 130 / Issue 3 / BIOACOUSTICS [80]

Vocal cues indicate level of arousal in infant African elephant roars

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1700-1710 (2011); (11 pages)

Angela S. Stoeger1, Benjamin D. Charlton1, Helmut Kratochvil2, and W. Tecumseh Fitch3

1 University of Vienna, Department of Cognitive Biology, Althanstrasse 14, A-1090 Vienna, Austria
2University of Vienna, Department of Evolutionary Biology, Althanstrasse 14, A-1090 Vienna, Austria
3University of Vienna, Department of Cognitive Biology, Althanstrasse 14, A-1090 Vienna, Austria

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Arousal-based physiological changes influence acoustic features of vocalizations in mammals. In particular, nonlinear phenomena are thought to convey information about the caller’s arousal state. This hypothesis was tested in the infant African elephant (Loxodonta africana) roar, a call type produced in situations of arousal and distress. Ninety-two percent of roars exhibited nonlinear phenomena, with chaos being the most common type. Acoustic irregularities were strongly associated with elevated fundamental frequency values. Roars produced in situations of highest urgency, based on the occurrence of behavioral indicators of arousal, were characterized by the lowest harmonics-to-noise ratio; this indicates low tonality. In addition, roars produced in these situations lasted longer than those produced in contexts of lower presumed urgency. Testing the infant roars for individual distinctiveness revealed only a moderate classification result. Combined, these findings indicate that infant African elephant roars primarily function to signal the caller’s arousal state. The effective communication of this type of information may allow mothers to respond differentially based on their infant’s degree of need and may be crucial for the survival of infant African elephants in their natural environment.

© 2011 Acoustical Society of America

ACKNOWLEDGMENTS

We are grateful to the Vienna Zoo and the Viennese elephant keepers as well as Dr. Daphne Sheldrick and her team, for providing us the opportunity to collect data at their institutions. We acknowledge AKG Acoustics for supporting the project with the AKG 480 B microphone and the condenser capsule CK 62. Special thanks go to Anton Baotic, who reanalyzed the data to provide a quantified reliability check for the visual categorization of NLP classes. We are very grateful to Joseph Soltis and one anonymous reviewer for their very helpful and constructive comments on a previous version of this manuscript. The research was financially supported by the FWF Austrian Science Fund to A. Stoeger and the ERC Grant SOMACCA to W. Tecumseh Fitch.

Article Outline

  1. INTRODUCTION
    1. Acoustic cues to arousal in nonhuman mammals
    2. NLP in nonhuman mammals
    3. Infant African elephant vocalizations
  2. METHODS
    1. Subjects and study site
    2. Vocal recording and behavioral observations
    3. Definition of arousal states and behavioral contexts
    4. Acoustic analyses
    5. Statistical analyses
  3. RESULTS
    1. Description of acoustic structure including NLP
    2. Acoustic variation by individuals
    3. Acoustic variation by behavioral context
  4. DISCUSSION
    1. Description of acoustic structure including NLP
    2. Acoustic variation according to individuals
    3. Acoustic variation according to behavioral categories
  5. CONCLUSIONS

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KEYWORDS and PACS

Keywords

bioacoustics, biocommunications, chaos, nonlinear acoustics, zoology

PACS

  • 43.80.Ka

    Sound production by animals: mechanisms, characteristics, populations, biosonar

ARTICLE DATA

History
Received 24 Jul 2010
Accepted 27 May 2011
Revised 16 May 2011
Digital Object Identifier
http://dx.doi.org/10.1121/1.3605538

PUBLICATION DATA

ISSN

0001-4966 (print)  

Publisher

$abstract.society.value is a Member of CrossRef Acoustical Society of America

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