Nonlinear phenomena in the natural howling of a dog-wolf mix

It was reported to the first author that a female dog-wolf mix showed anomalously rough-sounding vocalization. Spectral analysis of recordings of the vocalization revealed frequency occurrences of subharmonics, biphonation (two independent pitches) and chaos. Since these nonlinear phenomena are currently widely discussed as integral to mammalian vocalization Wilden et al., Bioacoustics 9, 171-196 (1988)] or as indicators of vocal pathologies Herzel et al., J. Speech Hearing Res. 37, 1008-1019 (1994); Riede et al., Z. Sgtkde 62 Suppl: 198-203 (1997)], we sought to understand the production mechanism of the observed vocal instabilities. First the frequency of nonlinear phenomena in the calls was determined for the female and four additional individuals. It turned out that these phenomena appear, but much less frequently in the repertoire of the four other animals. The larynges of the female and two other individuals were dissected post mortem. There was no apparent asymmetry of the vocal folds but a slight asymmetry of the arytenoid cartilages. The most pronounced difference, however, was an upward extension of both vocal folds of the female. This feature is reminiscent of "vocal lips" (syn. "vocal membranes") in some primates and bats. Spectral analysis of the female's voice showed clear similarities with an intensively studied voice of a human who produces biphonation intentionally. Finally, the possible communicative relevance of nonlinear phenomena is discussed.