Orangutans are one of a kind. No great ape spends more of their life in trees, and outside of humans, no primate has a longer lifespan in the wild or spends longer raising their young. They’re also the least social of all the great apes and spend a lot of their lives alone, especially males. And let’s not forget their striking appearance. But orangutans still have much in common with their primate cousins (and over 1,500 other animal species that have been studied): when these orange-haired treefolk aren’t chilling in the leafy heights, they’re swinging both ways.
Scientists have documented same-sex behavior among orangutans since at least as far back as the 1960s, though they were reluctant to acknowledge it for what it was. For example, as part of a 1964 symposium at the Zoological Society of London, one researcher referred to a pair of orangutan males who spent a lot of time together and repeatedly engaged in anal intercourse as an example of an “irreversible sexual abnormality.” In his 1980 book, Orang-utan Behavior, another zoologist speculated that two male orangutans who regularly fellated one another might have been doing so in search of nutrition rather than sexual pleasure. Perhaps they weren’t getting enough (vitamin) D.
As time went on, experts eventually began to come around. In 1978, the researcher and conservationist H.D. Rijksen, studying Sumatran orangutans in the field, observed same-sex interactions between a pair of males named Sibujong and Bobo, which he described as homosexual. In his 1999 compendium of animal queerness, Biological Exuberance, biologist Bruce Bagemihl gathered decades of research showing the incredible range of orangutan bisexuality, including anal intercourse and mutual oral sex among males, and genital rubbing, cunnilingus, and fingering among females. Some males have even been seen trying to penetrate other males’ penises, which sounds tricky and rather painful. Orangutans have also been known to compete with each other for the attention of same-sex partners and voluntarily choose same-sex partners even when opposite-sex partners were available (often choosing both). Similarly, they form close same-sex bonds and attachments, including mutual grooming, hugging, kissing, food sharing, and getting into same-sex wrestling matches or other forms of play that become sexual. As Bagemihl noted:
Approximately 9% of all orangutan sexual encounters in some populations involve males mounting each other; the proportion of same-sex activity is probably even higher, since male oral-genital contacts and female homosexual encounters are not included in this figure.
It was long believed that orangutans partook in bisexual behavior primarily while in captivity and that it occurred less frequently in the wild. However, research has shown that orangs are as bi in the rainforest as they are in zoos. As a 2001 study in the American Journal of Primatology put it, same-sex behavior among orangutans “is not an artifact of captivity or contact with humans.”
Sadly, all three species of orangutan — Bornean, Sumatran, and Tapanuli — are considered “critically endangered”, primarily due to deforestation and habitat loss. What humanity does in the next few decades could very well determine the future of one of our closest cousins, and one of nature’s most remarkable bi tree-dwellers.