Monkeys have a very pervert sexuality. And one of the kinkiest species is the Barbary macaques (Macaca sylvanus). A new research published in "Animal Behavior" shows that males spy around in search of other pairs having sex so that they get a chance to copulate.

The same team lead by Dana Pfefferle of the German Primate Center in Göttingen had previously shown that female Barbary macaques stimulate males to ejaculate while having sex via calls during the ovulation period. During the infertile period, females having sex release different shouts, less exciting. But fertile females may also release non-ejaculatory yells.

Through a hidden speaker, the researchers played records of ejaculatory and non-ejaculatory calls released by both fertile and infertile females to males of Barbary macaques in French "La Forêt des Singes" (Forest of the Monkeys), a primate visiting center where these monkeys roam freely.
Males had strong reactions to the ejaculatory calls, searching in the direction of the sound for the mating pair. The female that emitted the calls was not around during the tests.

The ejaculatory calls turned on the males: they approached other females and checked their genital pads (in monkeys and apes, the bottom callosities swell and redden during the ovulation).

This is a sex war. Females are choosy, searching for the best male genes, while males just want to father as many offspring as possible. But females can be choosy or promiscuous depending on the social structure of the species. In gorillas' harem society, the females copulate only with the "big boy," the toughest male of the area. But in Barbary macaques, like in chimps and bonobos, females are all fertile at about the same time, and females and males copulate frequently in a promiscuous system.

"It's all about sperm competition. I think the female wants to get as much sperm as possible to 'choose' which genetic material is passed on to her offspring," Pfefferle told New Scientist.

The same team had found that even if the dominant males do not monopolize females in this monkey species, they father 80% of the offspring. The sperm competition has some advantages for the female: no male can be sure that it is not his offspring, so the offspring will be protected by all the males of the group. And male Barbary macaques are very involved in caring of the infants.

The researchers signal that the Barbary macaques, original from the mountains of northern Morocco and Algeria, and colonized on the Rock of Gibraltar (this is the only monkey roaming freely in Europe for centuries), are now menaced, with only 14,000 individuals surviving in the wild.

"Understanding what their strategies are to ensure high reproductive success may eventually help with conservation efforts, although at the moment the main threat to them is the destruction of their habitat," said Heistermann.