Perception of Male Caller Identity in Koalas (Phascolarctos cinereus): Acoustic Analysis and Playback Experiments

Abstract

The ability to signal individual identity using vocal signals and distinguish between conspecifics based on vocal cues is important in several mammal species. Furthermore, it can be important for receivers to differentiate between callers in reproductive contexts. In this study, we used acoustic analyses to determine whether male koala bellows are individually distinctive and to investigate the relative importance of different acoustic features for coding individuality. We then used a habituation-discrimination paradigm to investigate whether koalas discriminate between the bellow vocalisations of different male callers. Our results show that male koala bellows are highly individualized, and indicate that cues related to vocal tract filtering contribute the most to vocal identity. In addition, we found that male and female koalas habituated to the bellows of a specific male showed a significant dishabituation when they were presented with bellows from a novel male. The significant reduction in behavioural response to a final rehabituation playback shows this was not a chance rebound in response levels. Our findings indicate that male koala bellows are highly individually distinctive and that the identity of male callers is functionally relevant to male and female koalas during the breeding season. We go on to discuss the biological relevance of signalling identity in this species' sexual communication and the potential practical implications of our findings for acoustic monitoring of male population levels.

Cues to body size in the formant spacing of male koala (Phascolarctos cinereus) bellows: honesty in an exaggerated trait

“…Whether koalas attend to size-related formant information in male bellows remains to be demonstrated. However, in a previous study we showed that male and female koalas can discriminate between the bellows of different male callers and that formant-related spectral prominences contributed disproportionately to vocal identity (Charlton et al, 2011). Consequently, it seems likely that koalas perceive formant frequency-related variation in male bellows, and attend to this information in the context of identity cueing.…”

“…In a previous study we showed that clear spectral prominences likely to represent formants are present in male koala bellows (Charlton et al, 2011). If these pronounced frequency bands in male bellows are indeed formants, i.e.…”

“…Koala bellows consist of a continuous series of inhalations and shorter exhalations, and often have an introductory phase that is produced on exhalation and consists of abrupt amplitude onsets and offsets (Smith, 1980;Charlton et al, 2011) (see Fig.1). The exhalation and initial inhalation phases of male bellows have five clear spectral prominences below 4000 and 3500Hz, respectively.…”

“…However, despite speculation about the possible functions of male koala bellows, it is not known whether male bellows have the potential to provide receivers with reliable information on the caller's physical attributes that are of potential importance in reproductive contexts. Koalas can distinguish between the bellows of different male callers (Charlton et al, 2011) and, thus, they attend to variation in the acoustic structure of these calls. In addition, male koalas are larger than females (Martin and Handasyde, 1999) and recent evidence shows that male reproductive output correlates with body mass .…”

Chemosensory discrimination of identity and familiarity in koalas

“…The relatively low rate of male agonistic interactions that are observed during the breeding season is most likely to be a direct consequence of this species' predominantly arboreal and nocturnal lifestyle which makes behavioural observations difficult (Martin and Handasyde, 1999;Melzer et al, 2010;Mitchell, 1990) but could also imply that competitive interactions are often resolved through signalling (as in other mammals: Bradbury and Vehrencamp, 2011). Consistent with this notion, recent work has revealed the importance of male bellow vocalisations in this species' vocal communication system for signalling identity and deterring potential rivals (Charlton et al, 2011;Charlton et al, 2013).…”