Male koalas use unique vocal organ to create deep pitch mating calls BRIGHTON, England, Dec. 2 (UPI) -- Male koalas' mating calls, much lower than the Australian marsupial's relatively small size would suggest, are down to a unique vocal organ, scientists say. The calls, more than 20 times lower in frequency than would be expected from an animal the size of a koala, are down to a specialized sound-producing organ never seen in any other land-dwelling mammal, they said. The distinguishing feature of this newly described organ is its location outside the voice box, what scientists call the larynx. "We have discovered that koalas possess an extra pair of vocal folds that are located outside the larynx, where the oral and nasal cavities connect," Benjamin Charlton of the University of Sussex in Britain said. We also demonstrated that koalas use these additional vocal folds to produce their extremely low-pitched mating calls. The extra vocal folds are similar to the laryngeal vocal folds of other mammals, the researchers said, but their location is highly unusual. The koala's bellow calls are produced on both inhalation and exhalation, similar to a donkey's braying, they said; on inhalation, koala bellows sound a bit like snoring, whereas when the animals exhale, the sound is more reminiscent of belching. "They are actually quite loud," Charlton said. "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.