Development and social dynamics of stone tool use in wild white-faced capuchin monkeys

Percussive tool use for extractive foraging allows animals to access otherwise inaccessible resources and forage more efficiently, with potentially important implications for their fitness. The development of tool use proficiency has been well documented in nut-cracking chimpanzees, Pan troglodytes , and robust capuchins, Sapajus spp., and in shellfish-cracking longtailed macaques, Macaca fascicularis , where mothers and proficient tool users are the most important models for social learning. However, little is known about how tool use develops in populations where opportunities for social learning are scarce. White-faced capuchins, Cebus capucinus imitator , on Jicarón Island, Panama, provide a unique opportunity to address this question: stone tool use is entirely male biased, meaning juveniles cannot learn from their mothers, and reduced group cohesion further limits opportunities for social learning. We investigated the acquisition and development of stone tool proficiency in this population using a data set collected over a 1-year period from camera traps placed at two experimental anvils. We assessed differences in proficiency between age classes, examined the development of tool use proficiency over time and explored patterns of social attention during tool use. Juvenile capuchins were less proficient than subadults and adults, but their proficiency remained stable over the 12-month study period, suggesting that skill development may require prolonged practice or physical maturation. In contrast to other primates, opportunities for social learning on Jicarón appeared to be limited and scrounging was rare, yet when social attention occurred, we found consistent patterns. Social attention to tool use mostly came from juveniles too young to use tools themselves, who observed proficient subadults that tolerated scrounging. Our results contribute to understanding how complex tool use behaviours are acquired and maintained. They highlight that even when tool use is largely solitary, directed social attention and social tolerance play an important role in the development of tool use proficiency.