Roaring by red deer stags advances the date of oestrus in hinds.

Some male mammals call loudly and repeatedly during the breeding season. Although the song of male birds is known to have effects on male-male competition, mate selection and ovulation, until now the loud calls of male mammals have been shown to affect only competition between males. Although it has been suggested that loud calling could also serve to attract females, the possibility that it has a direct effect on reproduction in females has not previously been investigated for any mammal. Here I report that roaring in red deer (Cervus elaphus) advances ovulation and that harem-holding males can improve their mating success by regular calling.