They are cute, cuddly and a favourite on any zoo tour. But when the male koala is looking to partner up, watch out. It produces an astonishing loud bass sound that is deeper than what scientists would expect of an animal that weighs no more than 20 pounds.
Judge for yourself in this YouTube video, in which a male koala sounds like a cross between a donkey braying, a frog croaking and a human belching.
According to research published this week in the periodical Current Biology, researchers found that male koalas can let out sounds that are as deep as what an elephant can produce – although the koala's vocal cords are much smaller.
Curious about what in koala's anatomy allowed the herbivore to manage such vocal lows, researchers examined the larynxes of 10 male koalas.
"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," Benjamin Charlton of Britain's University of Sussex said in a statement reported by Discovery News.
"We also demonstrated that koalas use these additional vocal folds to produce their extremely low-pitched mating calls," he said.
The male koalas showcase these sounds largely during mating season from September to December in their native Australia, where they sustain themselves on the leaves of the eucalyptus tree and 18 hours of sleep a day.