Loud Calls of the Yellow-Bellied Glider, Petaurus-Australis - Territorial Behavior by an Arboreal Marsupial

The yellow-bellied glider, Petaurus australis, is possibly the most vocal of all marsupials but little attention has been given to the functional significance of its calling behaviour. This study describes various traits of the calling behaviour and examines their significance. The traits were: (i) calling occurred throughout the night but was more frequent in the first 3 h of activity; (ii) calling frequency was significantly greater near the boundary (9.1 calls per 30 min) rather than the core (2 calls per 30 min) of glider home ranges; (iii) calling and gliding were highly correlated; (iv) calling rate was influenced by a glider's feeding behaviour; and (v) experimental playback of calls (simulating an intruder) resulted in calling rates by gliders that were significantly higher after the playback (6.3 calls per 15 min) than before the playback (2.8 calls per 15 min). Gliders approached the area of playback in 50% of tests; in one instance from a distance of 200 m. Assessment of the calling behaviour of gliders, by reference to seven functions proposed for loud calls of primates, indicates that the most likely function of calls is to mediate intergroup spacing. The traits of the calling behaviour, together with the observation that glider home ranges are virtually exclusive of those of neighbouring groups, suggest that calls serve a territorial function. The use of vocalisations appears to be the most effective method for advertising territories, which commonly exceed 50 ha. A review of the use of loud calls by other species of arboreal marsupial showed that at present there are insufficient data to enable an adequate assessment of the function of loud calls among these species.

Individual Recognition, Intragroup Cohesion and Intergroup Spacing: Evidence From Sound Playback To Forest Monkeys

The contexts and functions of several loud mangabey vocalizations, particularly the "whoopgobble", were investigated observationally and experimentally. Whoopgobbles are notable for their audibility and distinctiveness over long distances, their temporal pattern of delivery, and particularly their stereotypy and individual distinctiveness. On the other hand, contexts of and responses to these vocalizations are variable and sometimes nonobvious. In order to control context and more systematically investigate response, an experimental method involving playback of recorded vocalizations was developed. Although precautions against habituation were necessary, mangabey responses to playbacks were clearcut and repeatable. Answering vocalizations, changes in group movement, and changes in the dispersion of individuals within a group occurred only in response to mangabey vocalizations. Whoopgobble playbacks provoked a pattern of response, including most notably the rapid approach of one adult male (the "RA" male) from each group, which was specific to this call. Playback of whoopgobbles between 100 and 600m from mangabey groups indicated that this call does transmit information regarding the identity of the vocalizing individual and group over these distances. Test groups moved away from neighboring- and unknown-group calls, but towards those of their own males - particularly those of RA males. RA males, on the other hand, do not approach calls of other males from their own groups. Within a group, whoopgobbles may thus increase cohesion and influence the direction of movements. Characteristics of whoopgobble form and context are discussed with regard to hypothesized functions of these and other forest monkey loud calls. Responses by free-ranging mangabeys to playback of the whoopgobble confirm its role in maintaining distance between groups. Response was found to be independent of group size, despite the fact that whoopgobble rate is closely related to this variable and thus could transmit such information. Since responses were also found to be independent of location within the home range, intergroup spacing among mangabeys appears not be be "territorial", site defense does not occur. Nevertheless, the central areas in at least some mangabey groups' home ranges were never penetrated by neighbors. Playback tests with black-and-white colobus and blue monkeys, among which territorial spacing has been reported, indicate that responses to loud calls have some degree of site-specificity among these species. But the mangabey pattern of intergroup spacing appears to result from a combination of low group density, site attachment within groups, and site-independent avoidance between groups. These results emphasize that spacing "system" and "pattern" are not necessarily equivalent; a given set of spacing behaviors can result in different spacing patterns under different ecological conditions, while a given pattern may be obtained by any of several behavioral means. Evidence for site-independent spacing in other primate species is discussed.