Scientists have just turned up a second set of vocal cords in koalas. These bonus vocal cords allows males to hit tones 20 times lower than would be expected from an animal its size.
The size of an animal’s voice box and its flapping vocal cords dictate the range of pitches that an animal can make. For a typical 8-kilogram (17.5-pound) male koala, its voice should fall within the near-soprano range of any animal choir. Yet the male’s mating songs include very low bellows — tones usually created only by elephant-sized mammals. Although these tones may make a female koala swoon, to the human ear, the low-pitched sounds resemble only a string of belches and snorts.
A team of scientists wanted to probe how the serenading guys reach those deep bass tones. To find out, Benjamin Charlton led a team that dissected the voice boxes of 10 male koalas. A biologist who has worked in zoos, Charlton now works at the University of Sussex in Brighton, England.
His research group found that koalas possess a unique, second set of vocal flaps. The bonus ones reside outside of the voice box. Their placement allows them to belt out those low, low tones. These extra vocal cords make the koala quite unusual, both in terms of its anatomy and its acoustics —those sounds it makes, observe the scientists in the Dec. 2 issue of Current Biology.