An unusual relationship between a bull and a male donkey in Ethiopia has caught the attention of animal behaviour researchers. The two animals, named Achille and Patroclo, repeatedly seek each other out despite belonging to different species and having access to other potential partners. Their interactions include mounting, licking, rubbing and other affectionate behaviour, creating a rare example of a sustained socio-sexual relationship between two male animals from different taxonomic families.
The discovery was documented by researchers from the University of Pisa in a study published in the scientific journal Current Biology on November 2, 2026. During their observations, scientists recorded 51 mounting attempts involving the pair. The researchers say the case could help expand scientific understanding of animal sexuality, social bonding and behaviour that does not directly contribute to reproduction.
Meet Achille the Bull and Patroclo the Donkey
The unusual pair live on an Ethiopian plateau near Debre Libanos in the Oromia region. Achille is a male bull, while Patroclo is a male donkey.
The animals belong to different owners and live on separate farms. However, their herds sometimes share grazing areas, giving them opportunities to meet.
Researchers from the University of Pisa were originally conducting fieldwork on gelada baboons when they unexpectedly noticed the bull interacting sexually with the donkey.
The observation prompted the team to investigate the relationship more closely.
What made the situation particularly interesting was that the interactions were not isolated incidents. The researchers observed repeated encounters in which both animals actively participated.
The scientists named the pair after Achilles and Patroclus, two figures from Greek mythology whose close relationship is central to Homer’s Iliad.
Researchers Recorded 51 Mounting Attempts
The research team documented the animals’ interactions over a period in March 2026. Their observations recorded 51 mounting attempts involving Achille and Patroclo.
However, the behaviour extended beyond mounting.
The animals also displayed repeated affiliative interactions, including licking, rubbing and close physical contact. These behaviours were sometimes observed before mounting and frequently continued afterwards.
Researchers also noticed that Patroclo appeared to seek Achille’s attention and sometimes intervened when the bull showed interest in other animals.
The donkey reportedly displayed behaviour that discouraged other potential interactions, while continuing to engage with Achille.
Importantly, the researchers did not interpret the encounters as simple sexual aggression or coercion. They described the interactions as reciprocal and embedded within a broader social relationship.
The observations suggested that the animals repeatedly preferred each other’s company even when other potential partners were available.
Why the Relationship Surprised Scientists
Same-sex sexual behaviour is not unusual in the animal kingdom. Researchers have documented it across numerous species, including mammals, birds, reptiles and insects.
However, sustained sexual interactions between animals belonging to different taxonomic families are much less commonly documented.
The case involving Achille and Patroclo is unusual because it combines three characteristics:
- Different species: The animals belong to separate biological families, cattle and equids.
- Same-sex interactions: Both participants are male.
- Repeated social preference: They consistently sought each other out despite access to other potential partners.
The researchers argue that the relationship cannot easily be explained by a lack of mating opportunities or simple confusion between species.
Both animals had access to members of their own species and animals of the opposite sex. Nevertheless, they repeatedly directed their social and sexual interactions towards each other.
This suggests that the behaviour may be connected to a selective social bond rather than serving a reproductive purpose.
What Does the Study Reveal About Animal Sexuality?
The research adds to a growing body of scientific evidence showing that animal sexual behaviour is not exclusively driven by reproduction.
In many species, sexual interactions can also be associated with social bonding, cooperation, tension reduction and relationship formation.
Scientists have documented same-sex behaviour among animals such as Japanese macaques, bonobos, dolphins, penguins and several other species.
However, researchers have historically paid less attention to sexual behaviour that does not result in reproduction.
The University of Pisa team argues that these interactions deserve closer scientific investigation because they may reveal how animals develop and maintain social relationships.
In the case of Achille and Patroclo, the researchers suggest that their repeated interactions may indicate a social bond strong enough to outweigh the time and energy that could otherwise be spent on reproductive activities.
The study does not establish exactly what the animals experience emotionally. Scientists can document their behaviour, repeated preferences and physical interactions, but cannot directly determine their subjective feelings.
Scientists Caution Against Overinterpreting the Discovery
Although the discovery has attracted attention, researchers emphasise that one unusual case cannot explain animal sexuality across the entire animal kingdom.
The study documents a specific relationship between two individual animals under particular environmental and social conditions.
It does not establish that all same-sex animal interactions have the same purpose or that the behaviour necessarily reflects human concepts of romantic identity.
Scientists also need to distinguish between observable behaviour and interpretations of emotional experiences.
The researchers can demonstrate that Achille and Patroclo repeatedly interacted, displayed affiliative behaviour and engaged in mounting. Determining precisely what those interactions meant to the animals requires further investigation.
The findings are therefore best understood as evidence of an unusual social and sexual relationship rather than proof of a universal explanation for same-sex behaviour in animals.
Will Achille and Patroclo Meet Again?
The animals’ future interactions remain uncertain.
After the observation period, the researchers returned to their other work, and the animals were subsequently moved to different grazing areas as the local environment changed.
The research team hopes to arrange another opportunity for the animals to meet.
Further observations could help determine whether their relationship continues after an extended separation and whether the same behavioural patterns reappear.
Scientists would also like to investigate whether similar interspecies relationships occur more frequently than previously documented.
One challenge is that unusual animal behaviour can easily go unnoticed when researchers are studying something else. The discovery of Achille and Patroclo happened precisely because scientists happened to witness an unexpected interaction during unrelated fieldwork.
The Bigger Picture
The relationship between Achille and Patroclo highlights the complexity of animal social behaviour. It challenges the assumption that sexual interactions must always serve reproduction and shows how social relationships can develop across species boundaries.
The findings also underline the importance of observing animals in their natural environments. Behaviour that might appear unusual or insignificant in a brief encounter can reveal a much more complex pattern when studied systematically over time.
Looking Ahead
Researchers from the University of Pisa hope to continue investigating the pair and explore whether similar relationships exist elsewhere. A reunion between Achille and Patroclo could provide an opportunity to examine whether their interactions resume after separation and whether their social bond remains consistent. Further research may also help explain how sexual behaviour contributes to relationships that have no direct reproductive outcome.
For now, the bull and donkey remain a rare documented example of a sustained same-sex socio-sexual relationship between animals from different species. Their story offers scientists another reason to look beyond reproduction when studying animal behaviour and the many ways social bonds develop in nature.
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SEO Title: Bull and Male Donkey Form Rare Same-Sex Bond, Scientists Investigate
Meta Description: Researchers document 51 mounting attempts between a bull named Achille and a male donkey called Patroclo in Ethiopia, revealing an unusual interspecies social bond.
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Secondary Keywords: Achille and Patroclo, animal same-sex behaviour, interspecies animal relationships, University of Pisa study, Current Biology animal research, animal social bonding
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