A close relationship brings together a donkey and a bull in a rare sexual behavior between two different species

- In the highlands of the Ethiopian Plateau, a team of biologists was studying grass-feeding gelada monkeys when they came across unexpected sexual behavior between a male bull and a donkey belonging to two different species. Researchers observed the bull (Bos indicus) on top of the same donkey (Equus asinus) 51 times over four days in March.

The two animals did not live together, but rather met when their owners brought them, along with other animals, to graze in a common field, according to a study published by the journal "Current Biology" on November 2. “An unexpected encounter led us to ask a completely new research question,” said Elisabetta Balagi, assistant professor of biology at the University of Pisa in Italy and co-lead author of the study.

The donkey made no attempt to avoid the bull, but often offered his rear to him. Also, the bull was licking its body and gently headbutting it, which are common behaviors during mating between cows and bulls.

Evolutionary biologist Matilda Brindle, a postdoctoral researcher at the British University of Oxford, told Ofoq News, “Reports like this represent the first step towards understanding the true scope of sexual behaviors in animals.” Brindle, who was not involved in the study, added that scientists know little about non-reproductive sexual behaviors in animals, as they are often considered unimportant or even abnormal, and are not documented.

She emphasized that monitoring sexual interactions between animals of the same sex and different species helps to understand this aspect, which is still not sufficiently explored. Close connection: Researchers named the bull “Achilles” and the donkey “Patroclus,” after the two Greek heroes whose close relationship and mutual affection were discussed in Homer’s epic “The Iliad.”

“Their close connection is the focus of this story,” Balaghi told Ofoq News. She explained that Homer did not explicitly describe them as lovers, but writers from antiquity later interpreted their relationship as such.

The researchers monitored 34 cases of penetration out of the 51 times Achilles mounted Patroclus. It is not known when their relationship began, but local cattle herders were aware of the two animals' behavior before scientists arrived to start monitoring them.

Balaghi recalled that the researchers pointing their cameras at the two animals made the shepherds laugh, adding: “What was surprising to us was that it seemed to be a familiar sight to them.” Preference for Companionship Scientists have previously documented numerous cooperative behaviors among different species of animals, including sexual interactions.

These behaviors are not limited to males, as Brindle noted that female Japanese macaques climb onto the backs of sika deer and masturbate on them. Although these interactions are not reciprocal, the elk show little concern for the monkeys' actions.

Males mounting other males have also been recorded in different species of animals, and one of the well-known cases in the Netherlands is a male Mallard duck mounting another dead male of the same species. But what caught the attention of researchers in the case of Achilles and Patroclus was the frequency and confinement of their sexual behavior, in addition to the strength of their social connection.

The two animals were often seen close together, exchanging licking, rubbing, and courtship more than the rest of the animals in the field. "The two animals had access to other potential partners, of the same or other species, and of both sexes, but they preferred to stay together," Balaghi noted.

However, Achilles attempted to mount two other male donkeys on two occasions, but they rejected him by spreading their ears back and kicking him away. In contrast, Patroclus showed no aggression or discomfort when the bull was on top of him.

In one of the two attempts, Patroclus approached Achilles, and the bull immediately abandoned the other donkey and turned his attention to his usual partner. Likewise, Patroclus defended his relationship with Achilles on two occasions, baring his teeth and biting the sides of another bull that approached him and drove him away. “Perhaps they simply like each other.” Balaghi believes that the bull riding on top of the donkey may have contributed to the formation and strengthening of the social bond between them, but it is not clear whether this behavior began the relationship or appeared later.

She added that the domestication of animals partly explains their meeting in the same field, but it only explains a limited aspect of their story. “This study looks at a single pair of animals, so it cannot determine how common such relationships are or what benefits they provide,” she said.

“But it presents a systematically documented case, and raises broader questions about the resilience of social relationships in animals.” For her part, Brindle believes that the behavior of Achilles and Patroclus does not reveal a clear evolutionary strategy or benefit, but that does not make it abnormal behavior.

“Maybe they simply like each other,” she said. Even as Balaghi and her colleagues returned to studying gelada monkeys, they still wondered whether Achilles and Patroclus' relationship would stand the test of time.

The living conditions of domesticated animals are subject to the decisions of their owners, who may separate them regardless of the ties that unite them. After the researchers left Ethiopia, they learned that the shepherds separated the two animals and moved them to two different grazing areas, after the grasses in the field where they were collected were no longer sufficient.

“My students are back in Ethiopia and are trying to arrange for the two animals to meet again, after months of separation,” Balagi said. “If possible, we will document their encounter to see if they resume their previous interactions.”

“Until now, we cannot be certain that their relationship will continue during the period of separation.”