Characteristics of nonlinear phenomena in the tonal vocalizations of a North American canid, Canis rufus

Abstract

This study examines the structure and frequency of occurrence of nonlinear phenomena found in tonal vocalizations produced by red wolves. Spectrograms were obtained from audio tracks of digital video recordings of captive wolves from a breeding facility in Graham, WA. Tonal vocalizations were determined to be composed of 1–30 sound units, arranged in 1–5 phrases. Linear units included squeaks (2600–9600 Hz) and wuhs (100–1600 Hz); nonlinear units accounted for 22% of sounds and included between-type frequency jumps, harmonic and pure-tone biphonations, squeaks with sidebands, and squeak jumps. Five tonal vocalization types were identified based on unit composition: squeaks (48.4%), wuhs (19.3%), and three mixed vocalizations: banded squeaks (13.2%), complex squeaks (6.4%), and squeak-wuhs (12.2%). Unit order within a squeak-wuh vocalization was not random; transitions between units following a structural gradient most likely begin with higher frequency units and end with mixed or lower frequency units. The production of nonlinear sounds varied within and between individuals. The linear and nonlinear structure of red wolf tonal vocalizations are similar to that which has been reported in dholes and African wild dogs, and which have been indicated in reviews of published sonograms of gray wolf vocalizations.