Perception of size-related formant information in male koalas (Phascolarctos cinereus)

Advances in bioacoustics allow us to study the perceptual and functional relevance of individual acoustic parameters. Here, we use re-synthesised male koala bellows and a habituation–dishabituation paradigm to test the hypothesis that male koalas are sensitive to shifts in formant frequencies corresponding to the natural variation in body size between a large and small adult male. We found that males habituated to bellows, in which the formants had been shifted to simulate a large or small male displayed a significant increase in behavioural response (dishabituation) when they were presented with bellows simulating the alternate size variant. The rehabituation control, in which the behavioural response levels returned to that of the last playbacks of the habituation phase, indicates that this was not a chance increase in response levels. Our results provide clear evidence that male koalas perceive and attend to size-related formant information in their own species-specific vocalisations and suggest that formant perception is a widespread ability shared by marsupials and placental mammals, and perhaps by vertebrates more widely.