Perception of male caller identity in koalas (Phascolarctos cinereus): acoustic analysis and playback experiments
Charlton, BD, Ellis, WAH, McKinnon, AJ, Brumm, J, Nilsson, K & Tecumseh Fitch, W 2011, PLoS ONE, vol. 6, no. 5, e20329.
The bellow of a male koala is unique from that of other koalas to the extent that bellows can be consistently discriminated between and identified to individuals. Both male and female koalas that were familiar with the bellow of a particular male dishabituated in response to the bellow of an unfamiliar male and displayed comparatively greater interest in the novel stimulus.
Because of inter-individual morphological differences in the apparatuses involved in vocal production, such as the lungs, larynx and vocal tract, it is feasible that koala vocalisations, like human voices, can be distinct among individuals. This study found that the acoustic features of duration, stability, amplitude variation, and mean and maximum fundamental frequency could all be used to distinguish one bellow from another and even correctly assign recorded bellows to their callers for more than 80% of individuals. These acoustic features are predominantly related to the vocal filter features, rather than the vocal source features, of sound production. Differences in bellows were not only detectable by researchers, but also by koalas, with both male and female koalas able to determine whether a bellow was known or previously unknown.
Acoustic communication is likely to be an essential aspect of social interaction and organisation for the solitary and arboreal koala, especially during the breeding season, and the distinctiveness of individual male bellows has benefits for both male and female koalas. While bellows in general allow males to advertise their presence to others, the detection of specific individuals nearby may allow koalas to establish dominance relationships within overlapping territories as well as to avoid known rivals. Females may benefit from the ability to discriminate between male callers by using vocal cues to select a preferred mating partner based on familiarity, dominance or other qualities. Although koalas can differentiate between unique callers, it is not yet understood whether they are able to recognise specific individuals from their vocalisations.
As well as the biological implications for koalas of discriminating between male vocalisations, the findings of this study also have practical implications for the conservation and management of the species. Koala populations are notoriously difficult to monitor due to the species’ cryptic nature. As the bellows of koalas have been demonstrated to be individually unique, there is potential for using bioacoustic monitoring techniques to survey koala populations as a reliable measure of the number of males, and hence other conspecifics, within a population.
Summarised by Joanna Horsfall
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