(PhysOrg.com) -- Female bonobos are noisy bi-sexual love-makers that call most when mating with higher ranking partners, according to new research.
The new study by researchers at the University of St Andrews suggests that females produce copulation calls as a way of showing off high powered relationships during sexual interactions.
The psychologists set out to study vocal communication in apes, in particular investigating the social use of copulation calls in female bonobos.
Bonobos, the sister species of chimpanzees and closest living primate relative to humans, are known for their extensive use of non-reproductive sex for social purposes, such as making friends within groups.
Researcher Zanna Clay commented, During mating events, females of many primate species produce loud and distinct vocalisations known as copulation calls, which are considered to promote the callers reproductive success.
Female bonobos are unusual amongst the non-human apes in terms of their heightened socio-sexuality. We found that female bonobos engaged in frequent sexual interactions with both males and other females, while producing copulation calls in both contexts.
However, during same-sex mating, calls were always given by the lower-ranking partner, while the likelihood of calling increased with the partners rank, regardless of the partners gender.
The study, published in the latest edition of science journal Biology Letters, suggests that the increase in calls is a sign of signifying powerful friendships as well as pleasure.
The researcher concluded, Our results highlight the social significance of sex in this species and suggest that copulation calls in bonobos have undergone an evolutionary transition from a purely reproductive function to a more general social function.
Like humans, sex among bonobos is not only used for reproduction, but it is also important in friendships and bonding, and keeping close to those in power.
Explore further: Birds 'weigh' peanuts and choose heavier ones