Lateralization of mother-infant interactions in wild horses.

The manifestation of behavioural lateralization has been shown to be modified by environmental conditions, life experiences, and selective breeding. This study tests whether the lateralization recently found in feral domestic horse (Equus caballus) is evident in undomesticated horses. Mother-offspring interactions were investigated in Przewalski's horse (E. ferus przewalskii) living in their natural habitat in Mongolia. Lateral position preferences during mare-foal spontaneous reunions were used as a behavioural marker of visual lateralization. Preferences were separately assessed for foals' approaches to their mothers and mares' approaches to their foals. Preference to keep the mother in the visual field of the left eye was found in various types of foals' behaviour. In slow travelling, Przewalski's foals showed stronger preference for the left eye use than feral horse foals. Population-level left-eye bias was also found in mothers approaching their foals. Our results indicate right-hemispheric dominance for control of mother-offspring interactions in Przewalski's horses, similar to what has been reported for other mammals including humans. Benefits conferred by the lateralized social processing of and responding to social stimuli may explain that the left-lateralized social behaviour is a robust trait of equine behaviour, not modified by domestication or specific environmental conditions of the population.