Across the animal kingdom we kind find numerous examples of creatures that make noises to attract a mate. Some are well known, such as the call of the frog or sound of a cricket, while others are less so. What sound does a koala make? The male koala is surprisingly vocal and produces a sound that could be compared to a lion. The low rumbling sound seems almost magical as it comes from such a small animal. Benjamin Charlton from the University of Vienna was interested in this unusual juxtaposition of the deep sonorous noise and the diminutive marsupial and with a team of international co-researchers they set about trying to provide some explanations.

In humans, the size and depth of our voice box, or larynx, directly corresponds to our ability to produce deeper sounds. This is also true for the koala, but looking at the size of the animal you might predict it to produce a higher tone, maybe comparable to a cat or a small dog. The bellowing sound of a koala might suggest an animal the size of a hippo. So, how does it do it? Charlton's discoveries, published in the Journal of Experimental Biology, revealed some of their secrets.

They found that the organisation of the animal's vocal tract was very interesting. Their larynx is descended, an uncommon trait that humans also share, and that the muscle tissue connecting the sternum to the larynx may even be able to pull it down deeper into the chest.

The result of this is that koalas can produce a sound that would suggest an animal with a vocal tract measuring as much as 50 cm. This brings it into the same range as animals as large as bison.

Why might a koala need to make such a sound? What would drive the evolution of such an unusual talent? Charlton theorises that it may be some form of exaggeration used when competing with rival males. Rivals hearing the deep calls might think that they were about to face a giant and thus avoid confrontation. This advantage over time could favour deeper and deeper calls and result in the sounds they are now capable of.

So, if you are walking in the Australian bush and hear a monstrous call, take a moment to consider that it might not be as scary as it sounds!

Top Image Credit: Koala © HighlanderImages