Italian researchers documented a bull and a male donkey that formed a selective social and sexual bond on an Ethiopian plateau, according to a Cell Press release on a study in Current Biology. The bull and donkey bond included 51 mountings between the pair from March 6 to March 19, 2026.
The paper is titled “A socio-sexual bond between a bull and a male donkey.” The numbers carry the finding: the same bull mounted a second donkey twice in the same period.
What the Researchers Recorded
The two animals, a bull named Achille and a donkey named Patroclo, belonged to different owners and met only when they grazed on the same pasture. Both had access to partners of both sexes within their own species.
Over the two weeks, the researchers logged 51 mountings between the pair. That is about 3.6 a day, a calculation from the two figures. The bull mounted a second donkey only twice, and the release says that donkey showed avoidance signals such as flattened ears. The ratio of 51 to 2 means the bull directed about 25 times as many mountings at Patroclo, a calculation from the two counts.
How Patroclo Responded
Patroclo presented his hindquarters to the bull and nipped him without any defensive behavior, the release says. Licking, rubbing and nuzzling accompanied the mounting. That contrast is the core of the paper. Avoidance from one donkey and invitation from the other turns a count of mountings into evidence of choice. “This unusual sexual behavior was part of a broader, selective social relationship,” said Martina Francesconi, the lead author and a doctoral student at the University of Pisa, in the release.
What the Study Cannot Say
The authors say the study cannot establish what function the behavior serves. It covers a single pair of animals, and the observations were not experimental. The release presents the finding as a starting point for comparing social bonding across species. The case for caution is plain: one bull, one donkey and two weeks of footage do not support a claim about cattle or donkeys in general. What the paper does show is a documented bond that crossed species lines, with partners of their own kind available to both animals. The authors propose comparative research across species to test how common such bonds are.
