To vocalize, animals create sound waves in their pipe-like vocal tracts. Shorter pipes produce higher-frequency sounds, so small animals like the cuddly koala should have high voices. [koala sound] Or not.

A new study suggests that male koalas developed this low mating call to impress females with their size—even if they’re not quite as large as their bellows boast. The koala’s baritone is low enough to come from a 50-centimeter pipe, which should require a body larger than a bison.

Instead, males developed deceptively low voices by evolving a descended larynx, which means the voice box sits lower in the throat. This lengthens the vocal tract, which stretches between voice box and mouth, giving the koala a longer “pipe” and lower voice without a bigger body. The finding is in the Journal of Experimental Biology. [Benjamin Charlton et al., "Cues to body size in the formant spacing of male koala (Phascolarctos cinereus) bellows: Honesty in an exaggerated trait"]

Koala calls may be misleading, but larger males have even lower voices than their runtier counterparts. Which allows females to identify bigger, stronger mates. To these fuzzy bellowers, size does matter.

—Sophie Bushwick

[The above text is a transcript of this podcast.]

[Koala audio courtesy of Benjamin Charlton.]