Laterality in the use of the prehensile tail in the spider monkey (Ateles geoffroyi)

The purpose of this study was to assess the occurrence of lateral biases in the use of the prehensile tail in Ateles geoffroyi. 24 spider monkeys were presented with three food-reaching tasks designed to differ in the precision of motor control needed for successful food retrieval and assessed for lateral preferences in tail use with a minimum of 50 caudal reaches per animal and task. Highly lateralized tail use was found in 16 animals, distributed almost equally between left- and right-preferent individuals, consistent in strength and direction across tasks, and not significantly correlated with manual preferences. Eight infant monkeys did not cooperate suggesting an age-dependency in the development of tail use skills. The results give evidence of a hitherto undescribed example of behavioral asymmetry in a nonhuman primate species which may offer an additional approach to the investigation of cortical plasticity and functional hemispheric asymmetries.