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First published online January 5, 2005
Journal of Experimental Biology 208, 297-308 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01378

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Vocal tract filtering and sound radiation in a songbird

Brian S. Nelson^1,*, Gabriël J. L. Beckers^2,3 and Roderick A. Suthers^1,3

¹ Department of Biology, Indiana University, Bloomington, Indiana, 47405, USA
² Behavioural Biology, Institute of Biology, Leiden University, PO Box 9516, 2300RA, Leiden, The Netherlands
³ School of Medicine, Indiana University, Bloomington, Indiana, 47405, USA

^* Author for correspondence (e-mail: bsnelson{at}uoneuro.uoregon.edu)

Accepted 10 November 2004

Bird vocalizations resonate as they propagate through a relatively long trachea and radiate out from the oral cavity. Several studies have described the dynamics with which birds actively vary beak gape while singing and it has been hypothesized that birds vary beak gape as a mechanism for varying vocal tract resonances. Nevertheless, few studies have attempted to quantify the effects of beak gape on vocal tract resonances. We replaced eastern towhee, Pipilo erythrophthalmus L., syringes with a small speaker and obtained recordings of frequency sweeps while rotating each subject in a horizontal plane aligned with either the maxilla or mandible. We describe vocal tract resonances as well as how sound radiates as a function of beak gape. Results are inconsistent with the hypothesis that songbirds vary beak gape as a mechanism for `tracking' fundamental frequencies in vocalizations. Instead, decreases in beak gape seem to attenuate resonances that occur between 4 and 7.5 kHz. We propose that songbirds vary beak gape as a mechanism for excluding and/or concentrating energy within at least two distinct sound frequency channels.

Key words: songbird, vocal production, directional sound radiation, vocal tract resonance, beak gape

This article has been cited by other articles:

				T. Riede, R. A. Suthers, N. H. Fletcher, and W. E. Blevins Songbirds tune their vocal tract to the fundamental frequency of their song PNAS, April 4, 2006; 103(14): 5543 - 5548. [Abstract] [Full Text] [PDF]