The swollen red buttocks of female baboons are a turn-on for male baboons, and researchers have long assumed that the bigger the butt, the better. But new research by biologists at Duke University proves the sexual proclivities of male baboons are not quite that simple.

In studying the sexual behaviors of a group of baboons in southern Kenya, scientists found females with larger rumps weren't any more likely to attract mates than their peers with smaller buttocks.

The research also showed that big red butts weren't necessarily a sign of fertility. Females with bigger backsides weren't more likely to birth and raise a greater number of healthy babies.

"Some females are just bigger than others," Duke University researcher Courtney Fitzpatrick explained in a press release.

Fitzpatrick and her colleagues used special cameras to measure the size of females' swelling rumps from afar. In studying baboon breeding behavior, the researchers discovered that males prefer females who have had more menstrual cycles since their last pregnancy.

"It's almost as if the males are counting," Fitzpatrick said. "Our study suggests that, at least in part, males follow a rule along the lines of 'later is better' rather than 'bigger is better.'"

Fitzpatrick and her research team plan on continuing their observations to learn whether this strategy pays off or not. Do females that have had more post-pregnancy menstrual cycles end up mating with more males? And if so, does it lead to more bountiful, healthier offspring?

The latest research was published in the journal Animal Behaviour.