Australia's koalas have human-style voice boxes, allowing them to make a sound as loud as a cow that weighs more than a tonne, a new study has found.

Researchers discovered that male koalas in Australia emit loud bellows during mating season to attract sexual partners.

A team of Austrian and Australian scientists discovered the sounds were so loud because the larynx sat deeper in their throat and chest than other species. This is similar to human development because as an individual grows up, their larynx also becomes lower and deeper.

The volume of the bellows mean that koalas can make themselves sound far larger than they are. A 15-pound (just over one stone) koala can sound as loud as a one-tonne cow.

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As well as attracting mates, the bellows are a way of boasting about their body size and intimidating love rivals.

Dr Bill Ellis, a co-author of the study, said: "A lot of times people in the bush might hear a Koala calling… you have this cute fluffy animal but on the other hand (hear) this booming voice which jolts them a bit.”

He added: "To our ear, we can't actually hear much difference between a large and not so large koala, but it seems koalas can tell.”

The researchers studied the koalas at Lone Pine sanctuary in Queensland, Australia.