Researchers who travelled to Ethiopia to study monkeys came home with a very different story: a bull and a male donkey who kept choosing each other, again and again.
The pair, named Achille the bull and Patroclo the male donkey after Achilles and Patroclus from Homer’s Iliad, are the subject of a case study published on 2 November 2026 in the journal Current Biology. The authors say it is the first documented case of a sustained same-sex sexual relationship between a bull and a donkey.
51 mountings in four days
The team from the University of Pisa was in the Ethiopian highlands to study gelada monkeys, sometimes called bleeding-heart monkeys, when students noticed the pair in a shared pasture. Intrigued, they began observing them systematically: eight days between 6 and 19 March 2026, four days when the animals were together and four when they were apart.
On the four days together, Achille mounted Patroclo 51 times, 34 of which involved penetration. Patroclo was not a reluctant participant: he pressed his haunches toward the bull, nipped at him, and never kicked or tried to escape. The pair also licked, rubbed and nuzzled each other more often, and for longer, than they did with other animals. When Achille briefly mounted a different male donkey, that donkey showed clear avoidance and flattened its ears — and Patroclo moved in close until Achille returned to him.
What it means — and what it does not
The researchers are careful about what the behaviour means. “We interpret our data as a special relationship,” said Elisabetta Palagi, the evolutionary biologist who leads the team. Lead author Martina Francesconi added: “We believe the key finding is not simply that a bull mounted a male donkey.” The authors say the behaviour is not easily explained by a simple lack of other mating partners, and they cannot determine from this single case what function the interactions served.
Local herders, the researchers noted, were not surprised by the pair at all — they laughed when they saw the students filming. The scientists were. After the study, the two animals were moved to separate grazing areas, and whether the bond still exists is uncertain. What remains is a reminder that animal behaviour can be a more complex social phenomenon than a simple label allows.
Sources: Current Biology case study, 2 Nov 2026 (via Cell Press / Scimex); ScienceAlert, 2 Nov 2026; BBC Countryfile, 4 Nov 2026; UPI, 2 Nov 2026.
