Unusual Bond Between Male Donkey and Bull Baffles Scientists 2026

An unusual bond between a male donkey and a bull has left scientists baffled after they observed the two animals engaging in sexual and affectionate behavior. The case, reported in the journal Current Biology, is the first of its kind documented in scientific literature.

The animals, named Achille (the bull) and Patroclo (the donkey) after the Greek heroes of the Trojan War, were studied by researchers at the University of Pisa in Italy. Their interactions suggest that interspecies sexual behavior may be more complex than previously thought.

What Did Researchers Observe?

The team observed the bull and donkey licking and rubbing each other, with the bull sometimes mounting the donkey. While other donkeys avoided Achille's advances and showed threatening facial expressions, Patroclo often presented his hindquarters to Achille and nibbled him.

Dr Elisabetta Palagi, a co-author of the study, said: "It is really, really unusual. And it is the first time it is reported in literature." The researchers believe this behavior sheds new light on social and sexual interactions between animals.

How Was the Bond Discovered?

André da Cruz, a PhD student at the University of Pisa and another author, discovered the relationship by accident while studying geladas (also known as bleeding-heart monkeys) in Ethiopia. "We were having a little break for lunch, and in the distance I see something – it seemed a bit odd," said da Cruz. "I told colleagues: 'I think I saw a bull mounting a donkey.' And they didn't believe me."

The bull and the donkey belonged to different owners and only came into contact occasionally, making the observation even more remarkable. The study notes that the two males engaged in reciprocal grooming and sexual behavior, which is rare between different species.

Why Is This Significant?

This is the first documented case of a sexual relationship between a male donkey and a bull. While same-sex behavior has been observed in many species, interspecies sexual interactions are less common and often involve different social dynamics.

The findings could provide insights into how animals form bonds across species boundaries and how sexual behavior functions in social contexts. The researchers suggest that the relationship may serve to reduce tension or strengthen social ties, though more research is needed.

• First documented case of sexual behavior between a male donkey and a bull.
• Observed in Ethiopia by researchers from the University of Pisa.
• Behavior included licking, rubbing, mounting, and nibbling.
• Other donkeys avoided the bull, but Patroclo reciprocated.
• Published in the journal Current Biology.

What Does This Mean for Animal Behavior Studies?

This observation challenges assumptions about mating and social bonds in animals. It highlights the need for further research into interspecies interactions, especially in areas where domestic and wild animals overlap.

The study's authors emphasize that such behaviors are rare and not fully understood. They hope their findings will encourage other researchers to document similar cases, leading to a broader understanding of animal sexuality and sociality.

What to Watch Next

Researchers plan to continue studying the animals to see if the bond persists and whether it affects their social standing within the group. They also hope to identify other instances of interspecies sexual behavior in the region.

As scientists learn more about these interactions, they may revise theories about animal relationships and the flexibility of sexual behavior in the animal kingdom. The background to this story is set out in Celebrity: latest articles.