Researchers have described the relationship between a male donkey and a bull as highly unusual after observing repeated sexual and affiliative behaviours between the two animals. The findings, published in Current Biology, may offer new insight into how social and sexual interactions can overlap in animals.
The animals, named Patroclo and Achille, belonged to different owners and encountered each other only when their herds shared a pasture. During eight days of observation—four when both were present and four when only one was present—the researchers recorded 51 instances of Achille mounting Patroclo.
The team also observed the animals licking and rubbing each other. These behaviours frequently occurred both before and after mounting, suggesting that the interaction may have extended beyond sexual activity. Patroclo often presented his hindquarters to Achille and nibbled him, while other donkeys avoided the bull and displayed threatening facial expressions.
“It is really, really unusual,” said Dr Elisabetta Palagi of the University of Pisa, who co-authored the study. She said the behaviour was the first such case reported in the scientific literature.
The relationship was discovered by chance while André da Cruz, a University of Pisa PhD student and study author, was conducting research on geladas in Ethiopia. During a lunch break, he saw what appeared to be a bull mounting a donkey, an observation his colleagues initially doubted.
The researchers said there was no indication that the relationship involved force. They observed the animals seeking each other out, and Patroclo sometimes approached when Achille interacted with another animal. The donkey was also highly aggressive towards bulls other than Achille.
Da Cruz said the mounting was unlikely to be explained solely as an expression of dominance. The researchers observed signs that could have indicated ejaculation or orgasm, although they said this could not be confirmed. Achille also displayed courtship behaviour towards some female cattle, but neither animal was observed attempting to mount another member of its own species, male or female, despite having the opportunity.
Palagi said the case illustrated how sexual behaviour can become separated from reproduction. It remains unclear whether the animals’ social and sexual relationship existed from the beginning or whether one developed from the other. However, the researchers said the bond may have provided benefits through attention and possibly mutual support.
Josh Luke Davis, author of A Little Gay Natural History, said interspecies relationships and same-sex behaviours were not necessarily unusual in nature. He welcomed reporting such cases but cautioned against assigning them excessive significance or using them to support claims that homosexuality is unnatural.
Sources: The Guardian Science.