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, 70 (8), 1734-46

Coos, Booms, and Hoots: The Evolution of Closed-Mouth Vocal Behavior in Birds

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Coos, Booms, and Hoots: The Evolution of Closed-Mouth Vocal Behavior in Birds

Tobias Riede et al. Evolution.

Abstract

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 in birds and related outgroups. Ancestral-state optimizations of body size and vocal behavior indicate that closed-mouth vocalizations are unlikely to be ancestral in birds and have evolved independently at least 16 times within Aves, predominantly in large-bodied lineages. Closed-mouth vocalizations are rare in the small-bodied passerines. In light of these results and body size trends in nonavian dinosaurs, we suggest that the capacity for closed-mouth vocalization was present in at least some extinct nonavian dinosaurs. As in birds, this behavior may have been limited to sexually selected vocal displays, and hence would have co-occurred with open-mouthed vocalizations.

Keywords: Bioacoustics; hyoid skeleton; motor pattern; tongue; vocal production.

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