Koala calls

Source: scientias.nl
Koalas are peaceful animals. They sleep a great deal (18-22 hours a day) and spend a lot of time just eating eucalyptus leaves. At mating time, however, males make an enormous amount of noise.
It is suspected that the males roar and yell to attract females and to intimidate other males; a group of researchers has made this the focus of a study. The length of the animal’s vocal tract determines the sound it makes. The longer the tract, the lower the sound. In studying koala anatomy it was discovered that these animals’ vocal cords are situated very low in the vocal tract. Koalas can even contract muscles to pull their vocal cords deeper still into the chest cavity, creating an even lower sound.

Koala calls were recorded during the study, and the head sizes – a good measure of the size of the animal – were measured. The largest koalas produced the lowest sounds. The recordings were used to determine the length of the animals’ vocal tracts. The researchers were quite surprised to find that the animals sounded as if their vocal tracts were 50 cm long, equal to the entire length of a koala’s body! The sound of a koala call would seem to indicate that the animal is the size of a bison! It is speculated that they can sound larger than they are by allowing additional body cavities (nose, ears) to resonate as well.

Male koalas with a deep voice, then, are sending a message about how big they are.

The results of this study have been published in the Journal of Experimental Biology.