Hand preference by black-and-white snub-nosed monkeys (Rhinopithecus bieti) in captivity: influence of tasks and sexes.

Task complexity (Fagot & Vauclair 1991), bimanual complementary role differentiation (Uomini 2009), and the obligate use of a particular hemisphere (Rogers, 2009) have been proposed to explain why hand preferences in non-human primates are often influenced by tasks. We examined how tasks (reaching, carrying, extractive foraging, and object manipulation) and gender influenced hand preference in 11 adult black-and-white snub-nosed monkeys (Rhinopithecus bieti) out of a total of 13 known adult captive individuals of this species. A logistic regression was used to analyse 2556 bouts of binary left- vs right-hand use data. The explanatory variables are tasks, gender, and the interaction of tasks and gender. Hand preference is influenced by the task, in that subjects used the right hand significantly more often for extractive foraging and object manipulation than for reaching and carrying. We also found a significant interaction of sex and task: males used the left hand significantly more often than females for reaching and carrying, respectively, but not for extractive foraging or object manipulation. This is the first study on hand preference in R. bieti. As predicted, the hand preference in R. bieti is not a fixed property of the species or sexes but depends on the task.