A group of female capuchin monkeys in northern Brazil have developed an unusual method of attracting male sexual partners when they're in heat; they throw rocks at them. Writing in November's online journal, PLOS ONE, researchers say the practice could mark the evolution of learned behaviour, peculiar to one specific group.
DA CAPIVARA NATIONAL PARK (SCNP), PIAUÍ STATE, NORTHEASTERN BRAZIL (PLOS ONE) - In most primate species, the female will display physical signs of mating readiness to prospective male suitors through enlarged sexual organs, or by emitting specific scents. But one group of female capuchin monkeys in North Eastern Brazil prefers a more direct approach. When they're in their proceptive phase, they identify a potential paramour, and throw rocks at him.
The researchers were fascinated to observe that while three females in the PF group were seen throwing stones at males during their proceptive phases, the rock throwing behaviour was never observed in the other group of the same species.
"All throwing postures were overarm: the females held the stones at or above shoulder level before throwing it. They usually stood bipedally while throwing, but there were cases (not quantified) of throwing using a tripedal stance. The target males were always high-ranking individuals, but not always the alpha males," They wrote in the November edition of PLOS ONE. "Low-ranking males were never targets of stone throwing."
The scientists say it appears that rock-throwing is a learned behaviour within the PF group, "that is, the behavior was independently 'invented' by one or more females, and then copied by others as a form of "enhanced" display."
"We have perhaps, a unique opportunity to document the early phase of the diffusion of a new behavior, whose potential future dissemination history we are looking forward to following.' they said.