As the idiom puts it, beauty is in the eye of the beholder; but ears often get a look in too. Many species flaunt their charms with elaborate serenades or gruff grunts to woo the opposite sex. Scientists have long known that the pitch of an animal's call is related to its size, but you can't always rely on honesty when attracting a mate is at stake. Some species are more boastful than others; koalas have perfected the art of sounding larger than they really are with their deep bellows. Realising that male fallow deer also play fast and loose with their mating calls – producing deeper grunts than expected from the length of the vocal tract – David Reby from the University of Sussex, UK, and an international team of collaborators CT scanned the heads and necks of two fallow deer bucks to find out how they pull off their basso profundo performance.

Reconstructing the structure of the vocal and nasal tracts in 3D when relaxed and in the position that the throat takes during a grunt, the team found that the vocal tract (from the lips to the glottis) and the nasal tract (from the nostrils to the glottis) were ∼25% longer when the deer were grunting. The scientists then calculated the frequency spectrum of the grunt that the vocal tract should produce, but the major frequency components were out of sync with the frequency components that they had recorded from rutting bucks. However, when the team included the buck's nasal passages, they successfully reproduced the grunt spectrum. ‘This suggests that the vocal tract configuration during groan production is more complex than previously assumed’, says Reby, who is keen to learn whether other animals also croon through their noses.

M. T.
B. D.
J. P.
Vocal tract modelling in fallow deer: are male groans nasalized?
J. Exp. Biol.