'So we speculate that by lowering their minimum temperature each morning during rut, bulls increase their chance of winning a harem.

'By starting the day cool, a bull will enhance his capacity to store heat generated by the strenuous activity, thus prolonging the onset of heat stress.

'A bull that can sustain a contest for longer is more likely to win it and, so, control a herd of females and get more matings,' Grigg said, according to an UQ release.

Competing bulls perform elaborate, ritualised and intense competitive behaviour including posing and strutting side by side, inflating and exposing the dulaa (a sac-like extension of the palate), jostling, running together and, not always but often, actually fighting, says Grigg.

The study has been published online in Biology Letters.