Male koala's mating call produced using unique sound organ

Dec. 2 (UPI) -- The low-pitched mating call of male koalas has been linked to the presence of an additional sound-producing organ, seen for the first time in land mammals.

The pitch of a male koala is known to be 20 times lower than it should be, given the size of the koala. The location of this organ has been found to be outside the sound box, or larynx.

"We have discovered that koalas possess an extra pair of vocal folds that are located outside the larynx, where the oral and nasal cavities connect," said Benjamin Charlton of the University of Sussex. "We also demonstrated that koalas use these additional vocal folds to produce their extremely low-pitched mating calls."

A koalas bellows are similar to a snoring sound on inhalation and closer to the sound of belching on exhalation. The low-pitched sound is more typical of animals of a larger size, like a elephant.

Pitch is proportional to the size of the animal in that the dimensions of the vocal folds limit the lower frequency of sound an animal can produce. The koalas have gotten around this size constraint and developed extra folds to produce their low-pitched mating calls.

"To our knowledge, the only other example of a specialized sound-producing organ in mammals that is independent of the larynx are the phonic lips that toothed whales use to generate echolocation clicks," Charlton said.

[Current Biology]