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Cited by 38Animal Vocal Communication and BehaviorPhonetics and Phonology ResearchComparative Animal Anatomy Studies

A Chinese alligator in heliox: formant frequencies in a crocodilian

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Reber, Stephan A., Nishimura, Takeshi, Janisch, Judith, Robertson, Mark, Fitch, W. Tecumseh·2015·Journal of Experimental Biology
DOI 10.1242/jeb.119552PMC PMC4528706
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Abstract

Crocodilians are among the most vocal non-avian reptiles. Adults of both sexes produce loud vocalizations known as ‘bellows’ year round, with the highest rate during the mating season. Although the specific function of these vocalizations remains unclear, they may advertise the caller's body size, because relative size differences strongly affect courtship and territorial behaviour in crocodilians. In mammals and birds, a common mechanism for producing honest acoustic signals of body size is via formant frequencies (vocal tract resonances). To our knowledge, formants have to date never been documented in any non-avian reptile, and formants do not seem to play a role in the vocalizations of anurans. We tested for formants in crocodilian vocalizations by using playbacks to induce a female Chinese alligator (Alligator sinensis) to bellow in an airtight chamber. During vocalizations, the animal inhaled either normal air or a helium/oxygen mixture (heliox) in which the velocity of sound is increased. Although heliox allows normal respiration, it alters the formant distribution of the sound spectrum. An acoustic analysis of the calls showed that the source signal components remained constant under both conditions, but an upward shift of high-energy frequency bands was observed in heliox. We conclude that these frequency bands represent formants. We suggest that crocodilian vocalizations could thus provide an acoustic indication of body size via formants. Because birds and crocodilians share a common ancestor with all dinosaurs, a better understanding of their vocal production systems may also provide insight into the communication of extinct Archosaurians.

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  • Formants exist in the bellows produced by the Chinese alligator and likely also the American alligator.

    “Such formants exist in the bellows produced by the Chinese alligator (Alligator sinensis, Fauvel 1879) (Reber et al. 2015) and likely also the American alligator (Alligator mississippiensis, Daudin 1801) (Reber et al. 2017).”

    From Roars, Rumbles, and Resonance: A Systematic Review and Meta‐Analysis of Crocodylian Acoustic Signals (2026) · cites this paper as Reber et al. 2015

  • Vocalisations are composed of a fundamental frequency, harmonics, and for some species formants, all of which potentially modulate in frequency and amplitude across time.

    “Vocalisations, for example, are composed of a fundamental frequency, harmonics (Vergne et al. 2012), and for some species formants (Reber et al. 2015, 2017), all of which potentially modulate in frequency and amplitude across time (Vergne et al. 2012).”

    From Roars, Rumbles, and Resonance: A Systematic Review and Meta‐Analysis of Crocodylian Acoustic Signals (2026) · cites this paper as Reber et al. 2015

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Authors
Reber, S. A., Nishimura, T., Janisch, J., Robertson, M., & Fitch, W. T.
Affiliations
  • University of Vienna (AT)
  • Kyoto University (JP)
  • St Augustine Alligator Farm Zoological Park, St Augustine, FL 32080, USA
Corresponding author
  • Reber, Stephan A.
  • Fitch, W. Tecumseh
ORCID
Venue
Journal of Experimental Biology
Publisher
The Company of Biologists
Published
2015-08-01
Volume
218
Issue
15
Pages
2442-2447
ISSN
  • 0022-0949 (ISSN-L)
  • 1477-9145
DOI
10.1242/jeb.119552
PMC
PMC4528706
OpenAlex
W2228288576
Cited by
38
References
2
Citations by year
2026: 3 · 2025: 6 · 2024: 2 · 2023: 4 · 2022: 2 · 2021: 4 · 2020: 6 · 2019: 1 · 2018: 2 · 2017: 5 · 2015: 3
FWCI
2.90
Type
journal article
Language
en
Open access
Licence
Locations
  • Journal of Experimental Biology (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • Lund University Publications (Lund University) (submittedVersion)
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Developmental Biology › Animal Vocal Communication and Behavior
  • Social Sciences › Psychology › Experimental and Cognitive Psychology › Phonetics and Phonology Research
  • Health Sciences › Medicine › Urology › Comparative Animal Anatomy Studies
Keywords
bellows, formant frequencies, vocal tract resonance, acoustic communication, Alligator sinensis, heliox, playback experiments, archosaurs
MeSH terms
Alligators and Crocodiles, Animals, Cues, Female, Helium, Oxygen, Sound Spectrography, Vocalization, Animal, Body Size

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