Koalas' low-pitched voice explained by unique organ

Dec 02, 2013
This is a koala at Cape Otway. Credit: Benjamin Charlton

The pitch of male koalas' mating calls is about 20 times lower than it should be, given the Australian marsupial's relatively small size. Now, researchers reporting in the Cell Press journal Current Biology on December 2 have discovered their secret: koalas have a specialized sound-producing organ that has never before been seen in any other land-dwelling mammal. The key feature of this newly described organ is its location outside the voice box, what scientists call the larynx.

"We have discovered that possess an extra pair of vocal folds that are located outside the , where the oral and nasal cavities connect," says Benjamin Charlton of the University of Sussex. "We also demonstrated that koalas use these additional vocal folds to produce their extremely low-pitched mating calls."

The koala's bellow calls are produced as a continuous series of sounds on inhalation and exhalation, similar to a donkey's braying, Charlton explains. On inhalation, koala bellows sound a bit like snoring. As the animals exhale, the sound is more reminiscent of belching. And, as Charlton says, "they are actually quite loud."

They are also incredibly low-pitched, more typical of an animal the size of an elephant. Size is related to pitch in that the dimensions of the laryngeal vocal folds normally constrain the lowest frequency that an animal can generate. As a result, smaller species will typically give calls with higher frequencies than larger ones.

This video is not supported by your browser at this time.
This video shows the velar fold vibration at 10-45 Hz. Credit: Current Biology, Charlton et al

Koalas have bypassed that constraint by putting those vocal folds in a new location. Charlton describes the folds as two long, fleshy lips in the soft palette, just above the larynx at the junction between the oral and . They may not look all that different from the laryngeal of other mammals, but their location is highly unusual.

"To our knowledge, the only other example of a specialized sound-producing organ in mammals that is independent of the larynx are the phonic lips that toothed whales use to generate echolocation clicks," Charlton says.

The combination of morphological, video, and acoustic data in the new study represents the first evidence in a terrestrial mammal of an organ other than the larynx that is dedicated to sound production. Charlton says that he and his colleagues will now look more closely at other mammals to find out whether this vocal adaptation is truly unique to koalas.

Explore further: Green spaces don't ensure biodiversity in urban areas

More information: Current Biology, Charlton et al.: "Koalas use a novel vocal organ to produce unusually low-pitched mating calls"

Related Stories

Koalas' bellows boast about size

Sep 29, 2011

Koalas have a well-earned reputation for being dopey. Sleeping 19 hours out of every 24, and feeding for 3 of the remaining 5 hours, there doesn't seem to be much time for anything else in their lethargic lifestyle: that ...

Elephants sing low the same way humans do

Aug 03, 2012

(Phys.org) -- Mammals produce sounds in two ways, either via the flow of air over vocal folds (vocal chords), as in humans and many other mammals, or via active muscular contractions as in the cat’s purr. ...

A sing-song way to a cure for speech disorder

Oct 04, 2010

Hindustani singing, a North Indian traditional style of singing, and classical singing, such as the music of Puccini, Mozart and Wagner, vary greatly in technique and sound. Now, speech-language pathology ...

Recommended for you

'Divide and rule'—raven politics

5 hours ago

Mythology has attributed many supernatural features to ravens. Studies on the cognitive abilities of ravens have indeed revealed that they are exceptionally intelligent. Ravens live in complex social groups ...

Science casts light on sex in the orchard

Oct 30, 2014

Persimmons are among the small club of plants with separate sexes—individual trees are either male or female. Now scientists at the University of California, Davis, and Kyoto University in Japan have discovered ...

Four new dragon millipedes found in China

Oct 30, 2014

A team of speleobiologists from the South China Agriculture University and the Russian Academy of Sciences have described four new species of the dragon millipedes from southern China, two of which seem to ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.