Small koala, deep voice

When mating, male koalas vocalise fairly loudly - in a very low register. These sounds are much lower than one would expect to issue from the very small body of the koala. Now, finally, there is an explanation for this animal’s deep bass.
In general, small animals produce higher-pitched sounds and large animals lower-pitched tones. That’s not unusual: the size of the vocal folds determines the pitch of the sound produced. From the koala, a rather small animal, one would expect higher tones. The low tones it can produce seem more suited to a much larger animal – such as an elephant. These sounds are approximately twenty times lower than the size of the koala should dictate.

A researcher at the University of Sussex has now discovered how this can be. Koalas have an extra pair of vocal folds outside the larynx, where the nasal and oral cavities come together. This pair can be used both on inspiration and expiration, each producing a different sound, comparable to the braying of a donkey. The newly discovered process is how male koalas can make such loud, low sounds while trying to attract a female.

As far as we know, such a specialised sound-producing organ not connected to the larynx is present in only one other animal: the phonic lips with which the odontocete whales produce their clicks.