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Cited by 40Animal Vocal Communication and BehaviorAnimal Behavior and ReproductionMarine animal studies overview

Formants provide honest acoustic cues to body size in American alligators

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Reber, Stephan A., Janisch, Judith, Torregrosa, Kevin, Darlington, Jim, Vliet, Kent A., Fitch, W. Tecumseh·2017·Scientific Reports
DOI 10.1038/s41598-017-01948-1PMC PMC5431764
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Abstract

In many vertebrates, acoustic cues to body size are encoded in resonance frequencies of the vocal tract (“formants”), rather than in the rate of tissue vibration in the sound source (“pitch”). Anatomical constraints on the vocal tract’s size render formants honest cues to size in many bird and mammal species, but it is not clear whether this correlation evolved convergently in these two clades, or whether it is widespread among amniotes (mammals, birds, and non-avian reptiles). We investigated the potential for honest acoustic cues in the bellows of adult American alligators and found that formant spacing provided highly reliable cues to body size, while presumed correlates of the source signal did not. These findings held true for both sexes and for all bellows whether produced in or out of water. Because birds and crocodilians are the last extant Archosaurians and share common ancestry with all extinct dinosaurs, our findings support the hypothesis that dinosaurs used formants as cues to body size. The description of formants as honest signals in a non-avian reptile combined with previous evidence from birds and mammals strongly suggests that the principle of honest signalling via vocal tract resonances may be a broadly shared trait among amniotes.

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  • Vocalisations such as growls, roars, and bellows are produced by air pressure travelling through the laryngeal vocal folds causing them to vibrate through the trachea, with resonance produced by the vocal tract.

    “These include vocalisations such as growls, roars (in crocodiles) and bellows (in alligators), all of which are produced by air pressure travelling through the laryngeal vocal folds causing them to vibrate through the trachea, with resonance produced by the vocal tract (Riede et al. 2011; 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. 2017

    The Introduction identifies bellowing and roaring as crocodilian vocalisations, and the Discussion supports vocal-tract resonance in alligator bellows. But the Discussion explicitly says it remains unclear whether the vibrating tissue is the vocal folds, so the cited paper does not support that part of the proposed mechanism. The supplied passages have no page numbers. (LLM, conf=0.88)

    Experimental — accuracy not yet measured

  • This size-frequency relationship is based on whether vocal fold size (the main determinant of frequency) correlates with overall body size, which may not be the case for all species.

    “This size‐frequency relationship is based on whether vocal fold size (the main determinant of frequency) correlates with overall body size, which may not be the case for all species (Reber et al. 2017; Jensen et al. 2024).”

    From Roars, Rumbles, and Resonance: A Systematic Review and Meta‐Analysis of Crocodylian Acoustic Signals (2026) · cites this paper as Reber et al. 2017

    The Introduction (page unavailable) says that fundamental frequency reflects the rate of source-tissue vibration and that, in many species, it has no apparent link to body size, possibly because vibrating-tissue size is not tightly constrained by anatomy. This supports the claim that a size–frequency relationship need not hold across species, but the paper does not establish that vocal-fold size is the main determinant of frequency. (LLM, conf=0.81)

    Experimental — accuracy not yet measured

  • Sex appears to significantly predict some of the acoustic parameters of different call types, and dominant frequency (along with all formant-related parameters) in American alligator bellows is higher in females than in males, with this trend consistent across studies.

    “Sex appears to significantly predict some of the acoustic parameters of different call types.”

    From Roars, Rumbles, and Resonance: A Systematic Review and Meta‐Analysis of Crocodylian Acoustic Signals (2026) · cites this paper as Reber et al. 2017

    Split into 2 atoms — 0 confirmed, 2 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.

    Experimental — accuracy not yet measured

  • 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. 2017

  • 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. 2017

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Cited by

Sorted by citations

Authors
Reber, S. A., Janisch, J., Torregrosa, K., Darlington, J., Vliet, K. A., & Fitch, W. T.
Affiliations
  • University of Vienna (AT)
  • Wildlife Conservation Society (US)
  • University of Florida (US)
Corresponding author
  • Reber, Stephan A.
  • Fitch, W. Tecumseh
ORCID
Venue
Scientific Reports
Publisher
Springer Science and Business Media LLC
Published
2017-05-12
Volume
7
Issue
1
Pages
1816-1816
ISSN
2045-2322 (ISSN-L)
DOI
10.1038/s41598-017-01948-1
PMC
PMC5431764
OpenAlex
W2612365460
Cited by
40
References
4
Citations by year
2026: 2 · 2025: 7 · 2024: 3 · 2023: 4 · 2022: 4 · 2021: 7 · 2020: 7 · 2019: 2 · 2018: 4
FWCI
3.30
Type
journal article
Language
en
Open access
Licence
Locations
  • Scientific Reports (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • Phaidra (Universität Wien) (submittedVersion, cc-by-nc-nd)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
  • Lund University Publications (Lund University) (submittedVersion)
Funders
Austrian Science Fund (W-1234-G17, W 1234, 230604)
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Developmental Biology › Animal Vocal Communication and Behavior
  • Life Sciences › Agricultural and Biological Sciences › Ecology, Evolution, Behavior and Systematics › Animal Behavior and Reproduction
  • Physical Sciences › Environmental Science › Ecology › Marine animal studies overview
Keywords
formants, body size, honest signaling, Alligator mississippiensis, crocodilians, vocal tract resonance, bellows, acoustic communication, amniotes, dinosaurs, convergent evolution, sex differences
MeSH terms
Alligators and Crocodiles, Animals, Cues, Female, Male, Vocalization, Animal, Body Size

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