Why Koalas’ Mating Bellows Sound More Like a Choking Tiger, Less Like a Small, Cuddly Herbivore

If you heard a male koala bellow but did not see him, you might assume that some large, deadly creature was lurking behind the eucalyptus leaves. Half grunt, half chuckle, the koala's mating call, researchers determined several years ago, is about 20 times lower than the sounds other mammals of similar sizes make. Now, a new study reveals that koalas use a special pair of "fleshy lips" located outside of their larynx (or voice box) to produce these deep grunts.

These extra vocal folds—which, as far as the team knows, are unique among mammals—are situated at the opening between the animal's nasal and oral cavities. The Guardian explains the slightly morbid way the team verified the purpose of these odd folds:

To test whether these velar folds were behind the koala's strange vocalisations, the researchers got their hands on three (koala) cadavers. Then, with an endoscopic video camera in place to record the results, they attached “a 4.4 litre capacity pump” to suck air from the throat. This set-up mimics the koala’s calls pretty well.

Why koalas went out of their way to evolve this special organ remains an open question, the researchers report. Though most likely it has something to do with a female preference for deep, grizzly love calls.

More from Smithsonian.com:

Koalas and Kangaroos Have South American Roots 
The Sperm Whale's Deadly Call 

Rachel Nuwer | | READ MORE

Rachel Nuwer is a freelance science writer based in Brooklyn.