Hand Preference during Tool Use in Wild Bearded Capuchins

The preferential use of one limb (lateralization) has been observed in many species. This lateralization reflects functional asymmetries of the brain. Right-handedness and left-hemisphere dominance seem to be the norm in humans. However, suggestions that vertebrates, particularly non-human primates, show handedness are contentious. Tool use could be a driver of handedness. Here I investigated hand bias during tool use activities in groups of wild capuchins (Sapajus libidinosus). I observed the use of feeding tools in wild capuchin monkeys living in the dry Caatinga forests of the Serra da Capivara National Park, Piaui, Brazil. Capuchins used three major types of feeding tools: (a) tools for probing; (b) tools for pounding/cracking, and (c) digging stones to extract tubers or roots. I recorded hand use in 118 tool use bouts. These different types of tools had different motor demands; digging tools apparently favour right-hand use. The harsh Caatinga habitat poses a strong selective pressure for tool using, which might favour increased laterality and right-hand bias. However, the extent of right-handedness associated with tool use, particularly for digging, can only be fully evaluated following studies with larger sample sizes.