Probe tool use is, so far, the only known case in which wild capuchin monkeys modify objects used as tools: branches are trimmed off, and tips, thinned. Here we examine data of a two-year research on the use of sticks by two groups in Serra da Capivara National Park (PI), Brazil. This behavior is not usually observed among wild tufted capuchin (Sapajus spp.) populations, having been reported as a
... [Show full abstract] customary behavior only in SCNP groups. The probe tools are used to access small prey (insects or lizards) in rock cracks/trunks, or honey from wasps’ nests, and also to poke frogs and poisonous snakes. Tool preparation episodes involved up to 4 modification steps. Contrary to the stone tools used to crack hard nuts, probe tools do not present any weight constraint for use by females, but there is a strong male bias (97%) in the register of probe tool use. There is also no diet bias that could explain this difference. Although males hunt more often than females, the latter main prey items are lizards, which are also the main goal of probe tools. One possibility, about which we still do not have evidence, is that females may have fewer social opportunities to learn about probe tools.