A bull and a donkey in Ethiopia have struck up an unlikely romance in a rare case of same-sex bonding across species, researchers have said.
Scientists from the University of Pisa in Italy watched the bull, named Achille, mount the donkey, Patroclo, 51 times over just two weeks in March. The pair often followed up with what the researchers called “post-mounting contact” (licking and rubbing).
Same-sex behaviour is common in the animal kingdom, but it is rarely seen between different species. The findings suggest that animals can form close bonds across such lines – and that sex can be part of those relationships even when there is no chance of producing offspring.
“It was completely unexpected,” Dr Elisabetta Palagi, co-author of the study, told BBC Science Focus about the findings.
Palagi said the pair’s behaviour could not simply be put down to a lack of options: “Both animals had access to other potential partners, including animals of their own species and of both sexes. Yet they consistently chose to interact with one another.”
Instead, she suggested the relationship was a genuine one: “Social bonds can cross species boundaries, and sexual behaviour can be part of a relationship – even when it has no direct reproductive outcome.”
Martina Francesconi, the study’s lead author, added: “We believe the key finding is not simply that a bull mounted a male donkey. It is that this unusual sexual behaviour was part of a broader, selective social relationship.”
The team’s observations suggest the attraction was mutual. Patroclo never tried to kick or avoid Achille, and often presented his hindquarters to the bull and nipped him. The two also nuzzled, licked and rubbed each other, with this kind of friendly contact coming before a mounting in about a quarter of cases and after it in nearly three-quarters.
Palagi’s students named the animals after Achilles and Patroclus, the warriors whose close bond is central to Homer’s Iliad.
“Homer doesn’t explicitly describe them as lovers,” Palagi said, “although later ancient writers interpreted their relationship that way.”
The study was published in the journal Current Biology.
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