Specialized vocal organ gives koalas their deep voice

Nature : Despite their small size, male koalas have a mating call that is as deep-pitched as an elephant’s. To find out how such diminutive animals can produce such a low bass sound, Benjamin Charlton of the University of Sussex in the UK and colleagues looked more closely at the physical structure of the vocal tract. What they found was that not only do koalas have a descended larynx, which makes their vocal tract longer than expected, they also have a pharynx—located above the larynx—that comprises a set of “velar vocal folds,” or wrinkled membranes. Those membranes are heavier than the vocal cords and can stretch out to five times their length, allowing koalas to produce their signature low-frequency bellows. Why they do is still unknown, however: It’s been proposed that their deep rumblings could be useful for communicating over long distances or could make the koalas sound bigger than they really are.