Featured Research

from universities, journals, and other organizations

Koalas' bellows boast about size

Date:
October 1, 2011
Source:
The Company of Biologists
Summary:
Koalas are usually slothful until the mating season when they begin bellowing. Intrigued by the marsupial's strange sound, biologists decided to find out what messages the koalas' bellows may send and discovered that they are boasting about their size. The largest koalas produce deeper resonances than smaller males, and even the smallest males produce resonances that make them sound larger than a bison, which are 100 times their size.

Koalas are usually slothful until the mating season when they begin bellowing.
Credit: daphot75 / Fotolia

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 is until the mating season. Then the males begin bellowing. Benjamin Charlton from the University of Vienna, Austria, explains that they probably bellow to attract females and to intimidate other males. But what messages could these rumbling bellows communicate about their senders?

Intrigued by the marsupial's strange sound, biologists decided to find out what messages the koalas' bellows may send and discovered that they are boasting about their size. The largest koalas produce deeper resonances than smaller males, and even the smallest males produce resonances that make them sound larger than a bison, which are 100 times their size.

Charlton and an international team of collaborators publish their discovery that the koalas are boasting about their size in the Journal of Experimental Biology.

According to Charlton, they could be telling nearby listeners about their size. He explains that there was a possibility that koalas may be one of the few animals that have a descended larynx, which makes the vocal tract longer. Also, because all pipes -- including vocal tracts -- have frequencies where the air inside them vibrates naturally and amplifies sound, larger animals with longer vocal tracts produce lower resonances, giving their voices a more baritone quality. So, the longer vocal tracts of the largest koalas should produce deeper resonances to tell the listening koala audience just how big they are. Intrigued, Charlton, Tecumseh Fitch and their colleagues decided to find out whether male koalas have descended larynxes.

Teaming up with Allan McKinnon at Moggill Koala Hospital and Gary Cowin and William Ellis at the University of Queensland, Australia, Charlton investigated the anatomy of the marsupial's vocal tract. Using MRI and post-mortem studies, the team found that the koala's larynx had descended to the level of the 3rd and 4th cervical vertebrae, instead of being high in the throat. They were also surprised to find that the muscle that attaches the larynx to the sternum was anchored very deep in the thorax and they suggest that it could be involved in pulling the larynx even further down into the chest cavity.

But what effect does the koala's deeply descended larynx have on the acoustics of their bellows? Traveling to the Lone Pine Koala Sanctuary, home to 140 koalas, Charlton patiently recorded their rumbling bellows. He also measured the animals' head sizes, with the help of Jacqui Brumm and Karen Nilsson, as skull size is a good proxy for body size.

Back in the lab, Charlton analyzed the bellows' spectra and found that the largest males always had lower resonances than the smaller animals. More surprisingly, when Charlton calculated the koala's vocal tract length based on their acoustics, he was astonished to find that the koalas were able to make themselves sound as if they had 50-cm-long vocal tracts, nearly the entire length of the animal. In fact, the diminutive animals sound even larger than bison. Charlton suspects that koalas use the resonances of the oral and nasal tracts simultaneously to sound much larger than they are.

So, koala males are able to communicate their size, with the largest animals producing the richest baritone bellows. Charlton also suspects that the males' boastful bellows could have driven the evolution of their descended larynxes. 'Individuals that could elongate their vocal tracts by lowering the larynx may have gained advantages during sexual competition by sounding larger, and this would drive the evolution of laryngeal descent,' he says.


Story Source:

The above story is based on materials provided by The Company of Biologists. The original article was written by Kathryn Knight. Note: Materials may be edited for content and length.


Journal Reference:

  1. B. D. Charlton, W. A. H. Ellis, A. J. McKinnon, G. J. Cowin, J. Brumm, K. Nilsson, W. T. Fitch. Cues to body size in the formant spacing of male koala (Phascolarctos cinereus) bellows: honesty in an exaggerated trait. Journal of Experimental Biology, 2011; 214 (20): 3414 DOI: 10.1242/jeb.061358

Cite This Page:

The Company of Biologists. "Koalas' bellows boast about size." ScienceDaily. ScienceDaily, 1 October 2011. <www.sciencedaily.com/releases/2011/09/110929074201.htm>.
The Company of Biologists. (2011, October 1). Koalas' bellows boast about size. ScienceDaily. Retrieved July 28, 2014 from www.sciencedaily.com/releases/2011/09/110929074201.htm
The Company of Biologists. "Koalas' bellows boast about size." ScienceDaily. www.sciencedaily.com/releases/2011/09/110929074201.htm (accessed July 28, 2014).

Share This




More Plants & Animals News

Monday, July 28, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Raw: Sea Turtle Hatchlings Emerge from Nest

Raw: Sea Turtle Hatchlings Emerge from Nest

AP (July 27, 2014) A live-streaming webcam catches loggerhead sea turtle hatchlings emerging from a nest in the Florida Keys. (July 27) Video provided by AP
Powered by NewsLook.com
Trees Could Save More Than 850 Lives Each Year

Trees Could Save More Than 850 Lives Each Year

Newsy (July 27, 2014) A national study conducted by the USDA Forest Service found that trees collectively save more than 850 lives on an annual basis. Video provided by Newsy
Powered by NewsLook.com
What's To Blame For Worst Ebola Outbreak In History?

What's To Blame For Worst Ebola Outbreak In History?

Newsy (July 27, 2014) A U.S. doctor has tested positive for the deadly Ebola virus, as the worst-ever outbreak continues to grow. Video provided by Newsy
Powered by NewsLook.com
The New York Times Backs Pot Legalization

The New York Times Backs Pot Legalization

Newsy (July 27, 2014) The New York Times has officially endorsed the legalization of marijuana, but why now, and to what end? Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins