title: Coos, booms, and hoots: The evolution of closed-mouth vocal behavior in birds.
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.
authors.affiliation: Department of Physiology, Midwestern University, Glendale, Arizona, 85308. triede@midwestern.edu.
authors.forename: Tobias
authors.initials: T
authors.lastname: Riede
authors.affiliation: Department of Geological Sciences, The University of Texas at Austin, Texas, 78712.
authors.forename: Chad M
authors.initials: CM
authors.lastname: Eliason
authors.affiliation: Department of Biology, Memorial University, St. John's, Newfoundland and Labrador, A1B 3X9, Canada.
authors.forename: Edward H
authors.initials: EH
authors.lastname: Miller
authors.affiliation: Department of Biology, University of Utah, Salt Lake City, 84112, Utah.
authors.forename: Franz
authors.initials: F
authors.lastname: Goller
authors.affiliation: Department of Geological Sciences, The University of Texas at Austin, Texas, 78712.
authors.forename: Julia A
authors.initials: JA
authors.lastname: Clarke
mesh_terms: D000162:Acoustics; D000818:Animals; D005075:Biological Evolution; D001717:Birds / Q000502:physiology*; D008297:Male; D010802:Phylogeny; D014828:Vocalization, Animal
keywords: Bioacoustics; hyoid skeleton; motor pattern; tongue; vocal production