Acoustics of the avian vocal tract

The general principles underlying the acoustic performance of the avian vocal tract are examined both theoretically and experimentally. The formant resonances produced both by the total vocal tract and by the branchial tubes are evaluated quantitatively, and their dependence upon anatomical parameters is investigated. A simplified cylindrical model for the beak is examined theoretically, and experimental results are presented that confirm the predictions of the theory for this model. A similar theoretical and experimental investigation using a more realistic conical beak model is also reported, and behaves as predicted. Finally a theoretical study of the effect of mouth volume, as influenced by tongue position, is integrated with these other studies to produce a complete analysis. The implications of these studies for understanding the acoustical behavior of avian vocal tracts are discussed. (C) 1999 Acoustical Society of America. [S0001-4966(98)00912-6].