Sounds from humpback whale songs were analyzed to evaluate possible mechanisms of sound production. Song sounds fell along a continuum with trains of discrete pulses at one end and continuous tonal signals at the other. This graded vocal repertoire is comparable to that seen in false killer whales [Murray et al. (1998). J. Acoust. Soc. Am. 104, 1679-1688] and human singers, indicating that all three species generate sounds by varying the tension of pneumatically driven, vibrating membranes. Patterns in the spectral content of sounds and in nonlinear sound features show that resonating air chambers may also contribute to humpback whale sound production. Collectively, these findings suggest that categorizing individual units within songs into discrete types may obscure how singers modulate song features and illustrate how production-based characterizations of vocalizations can provide new insights into how humpback whales sing.

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The purpose of this study is to further understanding of the function of nonlinear vocalizations in red wolves (Canis rufus) by examining the acoustic, structural, and contextual characteristics of nonlinear sounds as compared to linear sounds. Video recordings of captive wolves from a breeding facility were analyzed. The acoustic nature of sound units was consistent with that of other social canids. The sound units included high-frequency squeaks (2600-9500 Hz) and low-frequency wuhs (160-1600 Hz) occurring either as separate units or in combination as nonlinear units (squeak-wuh frequency jumps, biphonations, squeaks with sidebands) and frequency jumps within squeaks. These low-amplitude sounds occurred in trains of 1-30 units that were classified as squeak vocalizations (49%), wuh vocalizations (19%), and nonlinear vocalizations (any combination including one or more nonlinear units, 32%). Nonlinear vocalizations transitioned directionally from high-frequency units to mixed-frequency units which has implications for the study of sound production and function. Wolves squeaked most often when oriented toward others, implying a solicitation function, while wuh vocalizations were more common during social interactions. Nonlinear vocalizations occurred most often during penmate-play or when oriented toward neighbors, indicating that nonlinear sound production may signal an increase in arousal.

Field measurements of sound propagation in a humpback whale habitat were collected to identify cues that a humpback whale might use to estimate its distance from sound sources. The data show that spectral cues are sufficient for estimating the relative distance a sound has traveled in such environments, and that several other cues may also provide useful information. It is suggested that listening humpback whales may use multiple cues in parallel to determine the range to singing whales.

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