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Roaring success? Keep it high

With their fearsome antlers, muscular bodies and impressive size, European red deer appear to be the epitome of masculinity. So why do the females of this species prefer stags with higher-pitched "feminine" calls?

This is the contradiction that is puzzling University of Sussex researchers. Dr David Reby and his colleagues Drs Ben Charlton and Karen McComb at the Mammal Vocal Communication and Cognition Research Group made the surprising discovery while playing male calls to red deer hinds that were at peak ovulation.

In general in the animal kingdom the deeper the male's call, the more attractive he is to females. The fundamental frequency, or 'pitch', of the roars reflects the rate of vibration of the vocal folds in the larynx. A lower pitch is typically associated with high testosterone levels, maleness and dominance.

In humans it is interpreted as an indicator of physical or social dominance and masculinity, and in some hunter-gatherer populations it is an indicator of male reproductive success.

But during a study at a deer farm in France, which involved red-deer stag roars being played though two separate speakers, David and his team noted that the females consistently went towards the speaker that played higher-pitched calls.

"Why females prefer more 'feminine' roars is still something of a mystery," says David. "I use 'feminine' here in an anthropomorphic way - obviously hinds do not have a concept of femininity or masculinity, and it is likely that the roars do sound very male to them."

He says there are several possible explanations for the results. It could be that high-pitched calls are characteristic of more active and sexually motivated males. It could also be that hinds prefer high-pitched roars as they sound more like the calls of their calves. In any case, hinds mating with males with higher pitched roars probably benefit from having 'successful' sons with high-pitched roars themselves.

The findings, which were published online in the Proceedings of the Royal Society B today (Wednesday 28 April), constitute the first evidence of a female preference based on the fundamental frequency of a male call in a non-human mammal - but crucially in the opposite direction to that normally assumed.

David points out that the pitch of the call in other species of deer also seems to be related to their size in a way that is unexpected. The North American Elk, which is among world's largest species of deer, has a call that's more like a whistle, while the diminutive Corsican deer has one of the deepest roars.