The meaning, structure and function of chimpanzee pant hoots from the Budongo forest, Uganda
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AbstractPant hoots are the species-typical loud calls produced by chimpanzees to communicate to conspecifics over long-distances. Previous studies have attempted to determine the degree to which pant hoots function as referential signals that communicate information specific to behavioural, social and ecological contexts but have produced mixed results. Uhlenbroek (1996, unpublished PhD thesis) identified three acoustically and functionally distinct sub-classes in pant hoots produced by chimpanzees from the Gombe Stream Reserve, Tanzania. Uhlenbroek labelled these variants "roar," "slow roar" and "wail" pant hoots and proposed they serve a referential function by being used in specific contexts. In this study, pant hoots were analyzed to determine whether similar functionally distinct vocal classes could be discerned in the Sonso chimpanzees of the Budongo Forest, Uganda. Using cluster and discriminant function analyses, three pant hoot types were identified quantitatively and a fourth type described qualitatively. Three of these pant hoot types exhibited varying degrees of production context specificity. However, contrary to Uhlenbroek, a strictly referential function for pant hoots is not proposed. Rather, I suggest that the structural characteristics of pant hoots are constrained by environmental, physiological and phylogenetic factors, and that the acoustic design of different pant hoot types conform to predictions concerning both motivational effect and propagation maximization in specific "layers" of the acoustic habitat. In addition, I propose the hypothesis that other acoustic cues, such as the presence of buttress drumming, the number of animals calling, the rate of calling per episode and the location of the caller relative to the ground, accompany many calls and are used by receivers to gauge the context and relevance of the call in determining a future course of action. In this manner, pant hoots might function referentially in a "weak" sense in that the interplay between the type of pant hoot produced and the suite of accompanying cues provide information concerning the context and "meaning" of the call.
Bibliography: p. 161-173