Female perception of size-related formant shifts in red deer, Cervus elaphus

Little is known about the role of specific acoustic cues in mammal vocal communication systems. Recent advances in bioacoustics allow us to use playback experiments in order to study the perceptual and functional relevance of individual acoustic parameters. In the current study we used re-synthesised male red deer roars in a habituation-discrimination paradigm to determine whether female red deer are sensitive to shifts in formant frequencies corresponding to the natural variation between the vocal tract lengths of a small and large adult red deer male. We found that hinds habituated to a given size variant show a significant dishabituation when they are presented with roars in which the formants have been modified to simulate the other size variant. The significant reduction in behavioural response to a final rehabituation playback shows this was not a chance rebound in response levels. Our results indicate that formants are salient for red deer hinds and that hinds can detect a shift in formant frequencies that has strong potential biological significance. We discuss the possible functions of formant perception in female red deer and more generally in nonhuman mammals.