Sounds big to me

Abstract

Many studies of animal sound communications have confirmed that vocal signals conveying some aspect of male quality can be used by females to influence their mate choice. Amongst mammals, however, there has been little evidence to show conclusively that this can be the case.But the roaring of red deer stags is known to affect the outcome of male–male interactions, advance female ovulation and influence mate attraction.Whereas earlier studies concentrated on more conspicuous features of the male call, such as roaring rate, more recent work has shown that hinds are able to discriminate between the roars of their harem holder and other stags and suggests that females have the ability to hear the finer acoustic structure of male roars.In a new study by Ben Charlton, David Reby and Karen McComb at the University of Sussex at Brighton, published in Biology Letters of the Royal Society (online), the researchers used re-synthesized calls and playback experiments at a deer farm at Redon, France, to examine the behavioural responses of oestrous red deer hinds to male roars in which a specific acoustic cue linked to body size — the formant frequencies — had been modified to simulate callers of different body size.Formants are the resonant frequencies of the vocal tract that can be seen as frequency peaks in the recorded structure of vocalisations.The team found that oestrous red deer hinds move preferentially towards male roars with lower formant values and spacing, simulating callers of larger body size. The results reveal the first evidence that a non-human female mammal uses an acoustic cue to body size in a mate choice context, the researchers say.“In our experiment, the movement of hinds towards the playback source simulating the presence of a stag is clearly equivalent to a mating choice/decision, and the preferential movement towards one type of stimulus can safely be assumed to reflect a mating preference.”Extrapolating to mate choice in the wild, the researchers believe this response pattern suggests that hinds, when given a choice between different-sized callers, will mate preferentially with males producing roars with lower formant values and may indicate the presence of directional selection on this feature of the male roar.The results suggest “that female mating preferences, for male roars in which lower formant values and spacing indicate larger callers, may have provided an additional selection pressure alongside male–male competition.”So a large stag's roar may not only help challenge a male rival in a clashing of antlers, it may attract potential female mates too.Pitch battles: New evidence suggests female red deer are attuned to the roars of males and prefer those of larger animals. (Photo: Laurie Campbell.)View Large Image | View Hi-Res Image | Download PowerPoint Slide