Local Herders Weren’t Surprised by the Bull and Donkey. The Scientists Published a Paper

A team of researchers went to the Ethiopian highlands to study gelada monkeys. Instead, they noticed a bull and a male donkey that kept finding their way back to each other in a shared pasture.⁴⁵

The pair is the subject of a case study published November 2, 2026, in the journal Current Biology, titled “A socio-sexual bond between a bull and a male donkey.”¹ The authors say it is the first documented case of a sustained same-sex sexual relationship between a bull and a donkey. That claim comes from the researchers themselves.⁵

It matters because other known sexual encounters between animals of different species are mostly linked to force or mistaken identity. Palagi said there was no indication of force here. The authors say the case offers a window into how social bonds and sexual behavior interact.²³⁷

What the researchers saw

The two animals had different owners and met only while grazing. Students working with co-author Elisabetta Palagi of the University of Pisa named them Achille and Patroclo, after Achilles and his companion Patroclus in the Iliad.¹⁴

Systematic observation covered eight days between March 6 and March 19, 2026: four days when the animals were together and four when they were apart. On the four days together, Achille mounted Patroclo 51 times. Neither animal showed sexual interest in members of its own species, even though other potential partners of both sexes were in the same field.³²

The contrast with other animals stood out. When the bull briefly mounted a different male donkey, that donkey showed clear avoidance and flattened its ears in a threat. Patroclo never avoided or kicked away the bull, and appeared to present his hindquarters to him.⁵⁶

When Achille mounted another donkey, Patroclo moved in close, and Achille ended up interacting with Patroclo instead, including licking his body.⁶

More than mounting

The pair also licked, rubbed and nuzzled each other more often, and for longer, than they did with other animals. They engaged in interactions after mounting more often than in foreplay, which the researchers read as suggesting the relationship involved more than sex alone.⁵⁶

“The sexual interactions between Achille, the bull, and Patroclo, the male donkey, were not isolated events,” Palagi said in the study’s release.² “It is really, really unusual,” she told the Guardian.⁷

The local herders were not surprised by the pair. The scientists were.⁴⁵

What the study can and can’t say

The researchers are careful about what the behavior means. “We interpret our data as a special relationship,” Palagi said, as reported by UPI.⁶ As quoted by Defector, she added: “We cannot say exactly what that relationship meant to Achille and Patroclo, but we can document how consistently they sought each other’s company and interacted.”⁴

Martina Francesconi, a colleague of lead author André da Cruz, was quoted by Scientific American as saying that because both animals are domesticated, their behavior may not reflect the social traits of wild animals.³

Palagi says future research should look at what mechanisms and benefits might lie behind interactions like these, and how social relationships shape sexual behavior.²

Where they are now

After the study, the two animals were moved to separate grazing areas. Palagi’s students are back in Ethiopia and plan to ask the herders whether the two can be reunited.⁴⁵