Female bonobos, often referred to as the pygmy chimpanzees, will often publicize their homosexual interactions to other females, particularly if an “alpha female” was nearby.
The latest research showed that females of this particular species will advertise their successes during sex by making copulation calls which are similar in acoustic structure as those made when mating with males, to tell other group members about the bond, especially if the sex was with a higher-ranking female.
"Using vocalisations, females only advertise sexual contacts with important group members," Dr. Zanna Clay, from Emory University in Atlanta, who has been studying vocalizations in the species for five years, told BBC. "It's all about climbing up the social ladder for female bonobos."
Zoologists noted that although homosexual genital contacts have been seen in all great apes, like the gorilla, common chimpanzee and orangutan, this sort of sexual behavior is “particularly strong and habitual” both in the wild and in captivity among the pan paniscus species.
"[Sex] is used to reduce stress and competition, develop affiliations, express and test social relationships and for reconciling conflicts and consoling victims in distress," Clay said.
Clay and her research group studied a group of bonobos at the Lola Ya Bonobo sanctuary in the Democratic Republic of Congo, Africa.
The team found that copulations calls were more likely to come from lower-ranking females, particularly if they were picked or chosen by a higher-ranking female, and they made more sounds if the alpha female was present.
"Bonobos appear to be highly aware of the dynamics governing their social worlds," said Clay, according to BBC.
The researchers said while the copulation calls were generally associated with reproduction, females of this species have used it as a strategic tool.
“Although copulation calls in bonobos most likely evolved within the reproductive context, they have become ritualized into broader, more flexible signals, used in both social and reproductive contexts,” the study authors wrote.
The researchers said that the study results demonstrated that female sexual interactions between these species are an important social mechanism for both low-ranked and high-ranked females.
“For low-ranked females, they can provide a means to develop associations and alliances with more dominant females, which can subsequently strengthen their social position within the group. For high-ranked females, interested in sexual interactions for other reasons, they may provide a means to assert their social position, develop new alliances and control the formation of others' social bonds,” the researchers explained.
In contrast to the species close relatives, the chimpanzees, bonobo societies are not patriarchal, which the researchers speculate could be the reason for the high frequency in homosexual relationships between females.
“Through intra-sexual tolerance and the development of female-female affiliations, female bonobos are able to form alliances and exert considerable power in their social groups,” they wrote.
“Female-female copulation calls, like the genital contacts they accompany, represent an example of an animal communication behavior that has been influenced by social life, becoming partly divorced from a purely reproductive function to acquire a broader social significance,” the authors concluded.
The study findings were published in the journal Scientific Reports on Thursday.