A bull and a donkey in Ethiopia form a bond scientists had never described
Achille, a bull, and Patroclo, a donkey, live on an Ethiopian plateau, belong to different owners and only meet at pasture. There they seek each other out, lick, rub and stay close, even with other animals around. Researchers at the University of Pisa describe it in Current Biology as a social and sexual bond between species. The caveat: it is a single pair, watched for two weeks.
They are called Achille and Patroclo, after the inseparable friends of the Iliad. Achille is a bull and Patroclo a donkey. They live on a plateau in Ethiopia, belong to different families and only see each other at pasture. And whenever they meet there, they look for each other.
A University of Pisa team spotted them while doing another field study. The pair caught their attention so much that, from 6 to 19 March 2026, the researchers logged every interaction. PhD student Martina Francesconi, the lead author, André B. da Cruz and ethologist Elisabetta Palagi are among the authors of the paper in Current Biology.
Licking, rubbing and choosing each other
The two animals licked, rubbed and nuzzled each other, and kept coming back to graze or rest side by side. The relationship also had a sexual side: the researchers counted 51 mountings between them, with no sign that the donkey tried to avoid it or defend himself.
What surprised them most was that the pair were not short of company. Both had other animals nearby, and the bull showed little interest in other donkeys: he tried to mount another one only twice, and that donkey flattened his ears and made threatening signals. That is why the authors describe the relationship as selective, not something explained by a lack of partners.
What is still unknown
The authors admit they cannot say what the bond is for. They suggest possible explanations, such as strengthening or maintaining the relationship or easing tension, and call for studies comparing more cases.
It is a single pair, watched for two weeks. It says nothing general about bulls or donkeys, but it is a well-documented case of two animals of different species choosing each other.
