Free-ranging red deer hinds show greater attentiveness to roars with formant frequencies typical of young males

Acoustic cues present in the reproductive calls of many animal species potentially encode important information about the caller. Here, we test the response of a free-ranging population of peri-oestrus red deer hinds to variation in a specific acoustic cue to body size in the male roar, the formant frequencies. Our results revealed: (1) that hinds showed greater overall attention (judged by longer looking responses and lower response latencies) to roars simulating males of sub-adult body size than to those simulating a large adult male and (2) that hinds without dependent offspring had greater looking responses to male roars and lower response latencies than hinds with dependent offspring to roars simulating sub-adult males. These findings indicate that free-ranging red deer hinds may use formants as acoustic cues to gauge the body size and maturity of males in their natural environment, possibly to facilitate earlier detection and avoidance of young stags that are known to harass them.