Cues and mechanisms for lateral exposure preference in the common eland (Taurotragus oryx)

Abstract: In vertebrates, brain lateralization has been described as a left hemispheric specialization for information processing and decision-making and a right hemispheric specialization for intense emotional reactions and fear responses. Accordingly, we may expect that ungulates will instinctively orientate their body in order to use their left eye for the detection of threats and social information. In this study, we investigate the factors influencing the body orientation of individuals during feeding activities in 55 captive common elands in two socially stable captive herds. Do lateralized postures differ while individuals perform activities with different vulnerability risks, and what are the factors affecting lateral exposure preferences? We recorded a large number of observations of the activity of the elands, the number of animals on each side, the positions and distances of the closest neighbour, the dominant individual and the closest visual barrier. Statistical analyses determined the positioning preferences of the animal according to these factors, including the influence of age, sex and ranking (own and that of the closest). At herd and individual levels, common elands have a left bias in lateral exposure preference to herdmates, dominant and closest individuals. Body orientation choice seems to be based on a trade-off between the perceived threat a nearby animal represents and the distance between them. Situations of higher vulnerability, like grazing, are characterized by a more intense lateralized pattern. This supports the theory that the animal would use its left side senses to more quickly and accurately detect and process danger and social stimuli. Significance statement: Common elands exhibit a left bias in lateral exposure preference to close surrounding individuals in order to process that information more efficiently with the right brain hemisphere. Body orientation choice is also based on a trade-off between the threat an animal in close proximity represents and the distance to it. Both tendencies are amplified when the dominant individual is present in the paddock. In the same way, situations of higher vulnerability degree, like grazing, are characterized by a more intense left bias in lateral exposure preference compared with other cognitive non-demanding activities like standing or ruminating.