Female capuchin monkeys throw stones to attract mates
Female capuchin monkeys have been filmed throwing stones at potential mates as a form of flirtation.
The primates whine, pull faces and follow potential mates around in scenes reminiscent of the school playground.
But scientists say this is a serious business for female capuchins as it is their only chance to secure a partner.
The previously unrecorded behaviour was filmed for the BBC/Discovery Channel co-production series Wild Brazil.
Filmmakers captured the footage of bearded capuchins - a subspecies of tufted capuchins - in Serra da Capivara National Park, Brazil.
Displays of affection
The monkeys live in the dry savannah-like habitat known as the Caatinga in north eastern Brazil.
Although their common name refers to their hairstyles, the monkeys' passionate side is hinted at in their scientific name Sapajus libidinosus.
Camila Galheigo Coelho from the University of Durham, UK, and the University of Sao Paolo, Brazil, has spent the last two years studying the social interactions of the monkeys for her PhD and helped filmmakers reveal the secrets of the capuchins' sex lives.
The monkeys are known for their intelligence after being recognised as the first non-ape primates recorded to use tools.
Their manipulation of stones - for cracking nuts, digging soil and investigating holes - has fascinated scientists for years and recent studies have focussed on the capuchins' ability to accurately aim and throw these stones.
Ms Coelho's colleagues Tiago Falotico and Prof Eduardo B. Ottoni recently published their description of the females' novel stone-throwing in the online journal PLoS One.
Unlike other monkeys, female capuchins do not have any physical indicators to show when they are at their most fertile or "proceptive".
End Quote Camila Galheigo Coelho University of Durham, UK and University of Sao Paolo, Brazil
Capuchin males will wait for the female to display full blown proceptive behaviour”
Without brightly coloured, swollen genitals or strong smelling odours or liquids to communicate, the capuchins display they are ready to mate through their behaviour.
The females solicit attention from males with pronounced pouting faces, whining calls or by touching them and dashing away.
This behaviour builds as the females pursue their mates and in the Serra da Capivara capuchins, it leads to females throwing stones directly at the subjects of their desire.
But rather than a signal of aggression, the stone-throwing is a compliment.
"Similar to the other primates where the male might wait until the swelling has reached its peak in size or redness, capuchin males will wait for the female to display full blown proceptive behaviour in order to guarantee copulation at the most fertile stage," explained Ms Coelho.
The biologist has been studying how individual behaviours can become more widespread traditions but she explained that this particular behaviour is unique to the Serra da Capivara group and is unlikely to be transmitted to others.
"It would be tricky for this behaviour to transfer. In capuchins the females stay with their groups for the rest of their lives - it's the males that migrate to other groups," she said.
"Other cultures of using stones or sticks have a better chance of transmitting because males migrate into neighbouring groups and end up spreading the behaviour."
Ms Coelho is now analysing her data to produce a "social network" of the capuchins' interactions.
"The idea is that I can see who is friends with who and map onto that how the behaviour spreads."
Wild Brazil begins on Tuesday 14 January at 2100 on BBC Two.