A socio-sexual bond between a bull and a male donkey.

A bull (Bos taurus/indicus) and a male donkey (Equus asinus) in a grazing area on the Ethiopian plateau (Debre Libanos, Oromia) showed repeated reciprocal socio-sexual interactions.

• Why it matters: Same-sex sexual behavior is common across animals, but cross-family observations are rare, making this unusual pairing important for understanding how social bonds can shape behavior.
• What they did: The authors report direct field observations of mounting attempts alongside repeated mutual affiliative interactions between Achille the bull and Patroclo the donkey.
• The result: The pattern suggests the behavior may reflect a strong social bond that could outweigh reproductive opportunity costs in time and energy for these two animals.

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