Communication during sex among female bonobos: effects of dominance, solicitation and audience

Bonobo females frequently form close bonds, which give them social power over other group members. One potential mechanism to facilitate female bonding is the performance of sexual interactions. Using naturalistic observations and experiments, we found various patterns that determined female-female sexual interactions. First, while low-ranked females interacted with all females, sexual interactions between high-ranked females were rare. Second, during genital contacts, females sometimes produced 'copulation calls', which were significantly affected by the rank of the caller and partner, as well as the solicitation direction. Third, there was a significant effect of the alpha female as a bystander, while variables relating to physical experience had no effects. Overall, results highlight the importance of sexual interactions for bonobo female social relations. Copulation calls are an important tool during this process, suggesting that they have become ritualised, beyond their reproductive function, to serve as broader social signals in flexible and potentially strategic ways.