Caller ID in Koala Calls

The phone rings, you answer, the caller says “hello, and” you instantly recognize the caller’s voice. This ability to recognize other individuals by their voice is also relatively common in baboons and other non-human primates. Until recently, this ability has not been demonstrated in marsupials.

Reporting in the online journal
PLoS One, Benjamin Charlton and colleagues (2011a) demonstrate that Koalas (Phascolarctos cinereus) may also have the ability to produce bellows that signal individual identity to other koalas. Koalas are solitary, mostly nocturnal, vegetarians. Male koalas produce loud low-pitched bellows or grunts that may be useful in reducing conflicts between males. In addition, bellowing frequency correlates with breeding activity and may provide cues for mate selection.

The researchers recorded male koalas bellowing and later played selected male bellows back to resting koalas (Figure 1). By recording their response to the playbacks, the researchers were able to demonstrate that male koala bellows are “highly individualized.” Interestingly, when they played the bellows of one male repeatedly to both male and females koalas, they eventually habituated to that male’s calls. However, they did respond to bellows from strange males.

koala
Figure 1. Left panels (a and b) show spectrograms of a male koala bellow. Bellows have a staccato introductory phase followed by a series of short “belch-like exhalations.” Panel (c) shows a male koala bellowing. (From Charlton et al., 2011a)

In a follow up paper in the
Journal of Experimental Biology (2011b) Charlton and his colleagues showed that koala bellows are the result of a unique anatomy. Male koalas have a permanently descended larynx, which is unique in marsupials. Evidently, koalas are able to retract the larynx into the thorax using a deeply anchored sternohyoid muscle. In addition, the vocal tract resonances (formats) produced during bellowing provide reliable information about the caller’s body size. Information on the caller’s body size may reduce conflict between males by providing advance warning about an interloper’s size. Likewise, female koalas probably use body size cues coded in the bellows to assess potential mates.

References
Charlton, B., Ellis, W., McKinnon, A., Brumm, J., Nilsson, K., & Fitch, W. (2011). Perception of Male Caller Identity in Koalas (Phascolarctos cinereus): Acoustic Analysis and Playback Experiments PLoS ONE, 6 (5) DOI: 10.1371/journal.pone.0020329

Charlton, B., Ellis, W., McKinnon, A., Cowin, G., Brumm, J., Nilsson, K., & Fitch, W. (2011). Cues to body size in the formant spacing of male koala (Phascolarctos cinereus) bellows: honesty in an exaggerated trait Journal of Experimental Biology, 214 (20), 3414-3422 DOI: 10.1242/jeb.061358