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Secret of koala bellow revealed

BBC Online
The loud, grumbling bellow that emerges from a male koala sounds very unlike that of a cute, laid-back creature. Now scientists have discovered the anatomy behind the strange sound that males make during mating season. Male koalas have very long vocal tracts - structures in their throats that produce the sounds.
Their vocal tract anatomy is so unusually specialised, in fact, that they are able to make sounds that make them sound far larger than they are. The study, reported in the Journal of Experimental Biology, used medical imaging to reveal that a male koala's voice box, or larynx, sits very low in its throat.
This "descended larynx" was thought to be a uniquely human feature - something that allows us to make the sounds we need for speech. It was only in 2001 that scientists found that red deer also had a descended larynx. Its discovery in koalas now proves that it evolved in non-mammals, possibly to allow males to distinguish themselves vocally from females.
The researchers studied the koalas at a sanctuary called Lone Pine in Queensland, Australia. As well as recording their bellows, the team also carried out a medical scan on one male koala, which revealed the marsupial's strange vocal anatomy.
"A permanently descended larynx hasn't been documented in marsupials before," said Ben Charlton from the University of Vienna, Austria, who led the study. "It was believed that only humans had [this, and] that it was an essential adaptation for the creation of vowel sounds."