Stone tool use in a new population of semi-free-ranging robust capuchins (Sapajus spp.) at Monkeyland Primate Sanctuary, South Africa.

Once thought to be uniquely human, tool use is now recognized in a range of non-human animals, with non-human primates frequently using tools in foraging contexts. Stone tool use is a common behavior in different species of capuchin monkeys, with evidence of behavioral and cultural differences across populations. In this study, we document stone tool use during percussive foraging in a previously unstudied population of capuchin monkeys at the Monkeyland Primate Sanctuary, South Africa. Of 87 mapped nut‑cracking sites, 77 yielded behavioral data comprising 1,359 recorded bouts. Capuchins showed a strong preference for organic anvils (roots n = 1,161, trunks n = 173, branches n = 23; with only 2 bouts on stone anvils) and used a wide range of hammer masses (25-1,581 g). Average nut‑cracking success was ~ 75%. Results show that nut-cracking success varies depending on both the capuchins' preferred hand and the size of the hammer they use. Additionally, we found strong individual differences in hand preference, which suggests that Monkeyland capuchins can adapt their techniques to improve their success. Because observations were limited to a subset of identified individuals between May andAugust, sex‑bias results are preliminary and future year‑round sampling is needed. Overall, our study adds to the growing body of research on capuchin cultural diversity by documenting tool use in a previously unstudied semi-free-ranging population. This preliminary assessment demonstrates the value of Monkeyland as a primate archaeology research site that preserves key ecological and social conditions while offering a unique balance between naturalistic behaviors and research accessibility.