Sydney, July 17 - When they want sex, male camels just have to stay cool.

This ability to drop their body temperature may help them last longer in rutting displays, says Gordon Grigg, emeritus professor at University of Queensland (UQ) School of Biological Sciences.

'Rutting involves very energetic daily display 'fighting' during which bulls contest ownership of a herd of females,' Grigg said.

'By starting each day cooler, a bull can postpone heat stress, compete for longer, win more contests and potentially sire more offspring.'

He said the ability of camels to drop body temperature in the mornings, invoking hypothermia, was once thought to be only a mechanism for conserving water in very hot dry conditions.

'But what we saw cannot be for saving water, we saw it only in winter, only in bulls during rut and, anyway, they had water freely available and used it routinely,' he said after a detailed study in the Australian desert, where thousands of camels roam free -- descendants of herds once brought from Asian countries.