Bonobos are notoriously promiscuous, with instances of group sex and females often engaging in same sex relations. Research published in the February edition of Biology Letters revealed that females cry out when copulating with either sex, and when two females are together, the lower ranking one cries out to signal her achievement.
"Female bonobos achieve power by forming coalitions with other females as well as males, so getting powerful female friends, and advertising it, matters," Zanna Clay, a primatologist at the University of St. Andrews University told LiveScience. "Like humans, sex among bonobos is not only used for reproduction, it is also important in other ways, such as friendship and bonding, and keeping close to powerful others."
Typically, female cries were seen to represent the ability to attract a superior partner and an aptitiude for sex, thus making themselves more attractive to other potential mates and increasing chances of reproducing. This recent study proves that the cries are used for other purposes.
When lower-ranking females copulate with either sex, it was found the chances of the inferior bonobo crying out increased as its partner's social ranking increased, irrespective of sex. This demonstrates that the main point of the cry is to announce new alliances -- but only the ones worth shouting about.
The endangered bonobo species are the closest living relatives to humans, along with chimpanzees, yet little is known about them. They can only be found in the wild in the Democratic Republic of Congo, making it difficult to study them for any extended period.
"The political instability and poor logistics of the Democratic Republic of Congo, as well as the forest's remoteness, mean that research on bonobos still remains a great challenge," explains Clay.
The team spent a year monitoring the animals, but Clay admits more research would be needed to understand how bonobos interpret the calls.
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