Secret of koala bellow revealed

Koala bellowing (Image: Ben Charlton/Journal of Experimental Biology) The males bellow during the mating season, probably to attract females and intimidate males

Related Stories

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 supports the theory that it evolved in even more branches of the evolutionary tree, probably 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 once believed that only humans had [this, and] that it was an essential adaptation for the creation of vowel sounds."

Dr Charlton explained to BBC Nature that the thing that made koalas "sound big" was not the just the very low pitch of their bellows, but the "quality" of the sound coming from their long vocal tract.

The effect works like a musical instrument; when an animal's "voice box" vibrates to make a sound, this sound echoes inside the tube that is its vocal tract. The dimensions of the tube change the sound.

So a violin and a cello can make a sound that is exactly the same pitch, but the cello sounds very different - richer and larger.

The sound of a koala's call, the researchers found, would "predict" a vocal tract length of 50cm. This is almost the entire body length of a koala. So when they bellow, the animals sound bigger than a bison.

The medical scans also revealed a muscle deep in the koala's chest that the researchers think might pull the voice box even further down into its chest cavity as they bellow, enabling them to exaggerate their size even more.

Dr Charlton explained that koalas had evolved to "sound big", "probably because it's important for intimidating other males."

There is also some evidence that the bellows attract females.

Red deer stag (Image: Simon King/ NPL) Red deer also have a descended larynx, a feature which had been thought to be unique to humans

David Reby is a psychologist from the University of Sussex in the UK who specialises in mammal communication. He led the team that, 10 years ago, discovered male red deer had a descended larynx.

Dr Reby explained how this study in koalas added to the wider evolutionary story of vocal communication. Finding out why male koalas evolved to make such deep, grumbling bellows could help us understand why male and female humans have very different voices, he said.

"Men have a 20% longer vocal tract than women," Dr Reby said. "To find out the evolutionary origin of this, we need to better understand how these [differences] evolved in other species.

"That's why Ben's work is really exciting, because he's not only studying other mammals but also marsupials."

The scientists would ultimately like to take live scans of the animals as they bellow - internal snapshots of what happens as they produce sound.

Dr Reby commented: "It would be difficult, but if we could get some good footage, we'd be able to figure out what was really going on."

Follow @BBCNature on Twitter

More on This Story

Related Stories

The BBC is not responsible for the content of external Internet sites

More from nature

  • Cardinal fish and ostracodFish filmed spitting 'fireworks'

    Film crew captures ostracods' spectacular defensive lightshow that makes predatory fish spit them out.

  • Arapaima'Locally extinct'

    A giant fish which used to dominate the Amazon river is now absent in many areas

  • DragonflyRapid reactions

    Dragonfly's super quick reactions recorded in slow motion by BBC film-makers

  • Wingless adult male of the midge Belgica antarcticaExtreme survivor

    Antarctic midge's small genome may be an adaptation to its extreme environment

  • Myotis midastactus specimen (previously identified as Myotis simus)Golden discovery

    A bat from Bolivia is described as a new species by scientists

  • Dinosaurs 'shrank' to become birds

    Huge meat-eating, land-living dinosaurs evolved into birds by constantly shrinking for over 50 million years, new research shows.

  • Would we starve without bees?

    Honey bees are under threat, and as pollination significantly contributes to the food we eat, what would we do without them?

  • Eggshells may act like 'sunblock'

    Birds' eggs show adaptations in pigment concentration and thickness to allow the right amount of sun for embryos, scientists say.

  • Female shrimps are more aggressive

    Female snapping shrimps are more aggressive than males when defending their territories despite their smaller claw size, a study shows.

BBC iWonder

  • Honey bee close-upInsect intelligence

    Are honey bees as smart as your sat nav?

  • Tyrannosaurus rex skull (c) Mark Williamson / Science Photo LibraryDinosaur dynasty

    One group of dinosaurs survived and their descendants can be seen all around us today

  • Brown rat cluse upRise of the rodent

    Reports of giant, 'super rats' are filling the headlines. But why are we being overrun by rats?

  • Cuckoo portraitHoliday hotspot

    What makes the UK such an attractive destination for visiting wildlife?

Awesome! And there's nothing common about such beauty.

Elaine Bernon on Facebook comments on the trio of common blue butterflies in our Photo of the Day.

Things To Do


More Nature Activities >

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.