Coos, booms, and hoots: The evolution of closed‐mouth vocal behavior in birds

  title={Coos, booms, and hoots: The evolution of closed‐mouth vocal behavior in birds},
  author={Tobias Riede and Chad M. Eliason and Edward H. Miller and Franz Goller and Julia A. Clarke},
Most birds vocalize with an open beak, but vocalization with a closed beak into an inflating cavity occurs in territorial or courtship displays in disparate species throughout birds. Closed‐mouth vocalizations generate resonance conditions that favor low‐frequency sounds. By contrast, open‐mouth vocalizations cover a wider frequency range. Here we describe closed‐mouth vocalizations of birds from functional and morphological perspectives and assess the distribution of closed‐mouth vocalizations… 

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