It is common that scientists observe male primates engaging in same-sex sexual behavior, but the same behavior is not well documented in females, until now.

Researchers who conducted a research trip in Rwanda Africa documented for the first time female gorillas having "lesbian sex." The activity includes mating calls during intercourse and genital rubbing.

According to team lead researcher, Dr. Cyril Grueter of the University of Western Australia, the wild mountain gorillas do it solely for pleasure and arousal rather than attraction, and they usually do it when they are rejected by male gorillas.

During their field study at the Virunga mountain range, which includes observation across the gorilla samples for two years, the researchers have observed that 18 of the 22 female gorillas engaged in same-sex sexual behavior around 44 times.

The same-sex sexual behavior occurred in adult and subadult, meaning age is not a determining factor for the engagement.

At an average, the same-sex copulation last for about 85 seconds.

"Most copulations involved solicitation behavior or courtship displays whereby a female would cautiously approach the partner and then stand facing partner with her body slightly turned to the side (as seen in heterosexual solicitation)," the author writes.

The study also found out that female gorillas are equally aroused by males and females.

The report concluded: "Same-sex sexual contacts among females are clearly a component of the behavioral repertoire of mountain gorillas, albeit a relatively infrequent one.

"Given that such homosexual interactions happened in a completely wild setting, the claim that it is an artifact of captivity is not applicable."

Grueter said in an interview with Daily Mail that the study will lead to further understanding of human evolution since gorillas are closely linked to humans.