Nonlinear phenomena in vertebrate vocal production

Abstract

Nonlinear phenomena such as subharmonics, biphonation (two independent frequencies), and deterministic chaos are widespread in animal communication. Examples from primate vocalizations, African wild dogs, hyena whoops, and bird songs are presented. Despite the variability of size and morphology, vocal production in vertebrates is governed by the same underlying mechanism: vibrating tissues such as vocal folds, membranes, or labia are driven by overcritical airflow. Consequently, sophisticated biomechanical-aerodynamic models of human voice production can serve as a starting point for modeling nonhuman vocal production. However, there is a variety of additional anatomical features in diverse species: pronounced air sacs, extensions of the vocal folds termed ‘‘vocal membranes’’ or ‘‘vocal lips,’’ or the coordinated action of left and right syrinx in song birds. It is shown that such specific features can induce voice instabilities. For instance, source-tract interactions lead to subharmonics and chaos, and vocal membranes allow multiple ‘‘registers.’’ Finally bifurcations in biomechanical models of the syrinx are discussed. [Work supported by the Deutsche Forschungsgemeinschaft (Grant He 2168/7).]