Wildlife

Puzzle of Koalas’ Unusually Deep Voices Solved: A Very Special Organ

Koalas are the Barry Whites of the animal kingdom, producing surprisingly low-pitched bellows.

A male koala, Iraga, in his enclosure at the zoo in Dresden, Germany, on November 22. Photograph by Sebastian Kahnert, AP

Now scientists have discovered the secret behind the Australian animal’s unusually deep voice: a special sound-producing organ not found in any other land mammal.

Koala bellows have a pitch about 20 times lower than they should be given the animals’ size—it’s actually more typical of an elephant-size animal. Male koala bellows, for instance, are so fearsome that sound designers used recordings of them to create the T. rex roars in the movie Jurassic Park.

For male koalas, this adaptation is essential to their love lives: A deep voice is attractive to female koalas choosing a mate. (Watch a koala video.)

Many animals, including koalas and people, produce sounds by passing air from the lungs over folds of skin located in the larynx, or voice box. When these folds, the vocal cords, vibrate, they make a sound. The size of the vocal cords determines the pitch of the sounds they create, so smaller animals will typically produce higher-pitched calls than larger ones.

The Lowdown on Low Voices

Male koala bellows are produced as a continuous series of sounds on inhalation and exhalation, like a donkey’s braying. Study co-author Benjamin Charlton, of the University of Sussex in the U.K., explained in a statement that during inhalation, koala bellows sound like snoring, and during exhalation, they sound more like belching.

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The scientists harvested body parts from wild koalas that had been humanely euthanized for other reasons. When scientists looked at the voice boxes of male koalas, they found their vocal cords weren’t large enough to create the animals’ extremely low-pitched mating bellows. But further examination revealed a second, much larger pair of vocal folds located outside of the larynx, where the oral and nasal cavities connect.

Charlton and his colleagues used a combination of physical, video, and acoustic analyses to demonstrate that the newly discovered vocal folds outside of the larynx are capable of producing extremely low-pitched sound as the koala inhales air through its nostrils. (Read more about koalas in National Geographic magazine.)

It’s the first evidence in a land-dwelling mammal of an organ other than the larynx that is devoted to producing sound.

The only other example of a specialized sound-producing organ in mammals that is independent of the larynx is the phonic lips that toothed whales use to generate echolocation—or the natural sonar that helps them find prey, said Charlton, whose study is published in the journal Current Biology.

But Charlton and colleagues plan to keep looking to find other animals with such low voices.

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Mary Bates is a freelance science writer living in Boston. She has a PhD in psychology from Brown University where she studied bat echolocation. You can visit her website at www.marybateswriter.com and follow her on Twitter at @mebwriter.
  • Ima Ryma

    Koalas have a quite deep pitch,
    So very low given the size.
    So scientists just got the itch
    To digging deeper for the whys.
    Some koalas did “volunteer”
    Their voice boxes for a look see.
    Extra vocal folds did appear.
    Outside of the larynx these be.
    Discovery that did excite.
    Koala sound solved – a big deal.
    The scientists expressed delight
    In long and varied high pitched squeal.

    Koalas – beware making sound,
    When scientists may be around.

    • Thanks for the awesome poem! I’m glad you liked the story.

  • kristal davis

    cool

  • Thomas Kelly

    Fascinating! Also, I really love the poem. Surely the koala has an opposite, a larger animal with a high pitch. Anyway, nice story!

  • Drew Fasick

    Very Interesting article, Mary, and great poem, Ima. One suggestion: After reading all about Koala bellows, I would love to hear what you’re talking about. I can probably hear it on the video linked, but I’d love a link to just a quick sound file. Thanks

  • Bellz

    Great poem. Love koalas. They can be a bit vicious too sometimes so watch out for their dew claws if its a little feisty.
    They can bite if they are injured & you are trying to help them.

  • Lungi
  • carlye

    I heard somewhere that elephants can make sounds at such a low frequency that it is not even audible to humans. Could that be with koalas?

  • fracturedempiricist

    So we are ignoring the existence of the “false” vocal chords cats use for purring then?

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