Hand preference on unimanual and bimanual tasks in Barbary macaques (Macaca sylvanus)

The presence of group-level handedness in non-human primates remains controversial, as different studies have produced inconsistent results. Bimanual coordinated tasks have been found to elicit more pronounced hand preferences than simple unimanual tasks. The aim of this study was to examine manual lateralization in a group of 15 Barbary macaques during unimanual and bimanual tasks. In the unimanual task, data on simple food reaching in a foraging context were collected. During the bimanual task, macaques had to use one hand to hold a tube-shaped apparatus while reaching with the other hand to retrieve the food inside it. Data on the hand use to retrieve food were collected. First, no significant group-level hand preference was found for the unimanual task. However, a significant right hand bias was evident for the bimanual task. At the individual-level, approximately 47% and 67% of the subjects had a significant hand preference in the unimanual and bimanual task respectively. The strength of the hand preference was greater in the bimanual than in the unimanual task. Findings of this study add Macaca sylvanus to the other species showing a right hand preference for coordinated bimanual tasks. Moreover, our results add to the growing body of evidence that bimanual tasks are more suitable and valid measures to investigate handedness in non-human primates.