Acoustics of the avian vocal tract

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