Supplementary data - Does the presence of conspecifics affect nutcracking behavior?

Although social learning in tool use among capuchin monkeys (Sapajus spp.) has been widely studied, the influence of conspecific presence on the nut-cracking behavior of adult capuchins remains largely unexplored despite evidence that capuchins are sensitive to conspecific presence in foraging contexts. We aimed at deepening our understanding of social presence effects on tool-use activity related to social context by testing whether adult tufted capuchin monkeys’ nut-cracking behavior varies with conspecific presence, and discussed how social rank and age influenced nut-cracking behavior. Studying a semi-free group of tufted capuchins at Tietê Ecological Park (TEP), São Paulo, Brazil we analyzed 80 nut-cracking episodes involving five proficient adults (three males, two females). Of these, 44 episodes involved at least one conspecific present. We ran Generalized Linear Mixed Models (GLMMs) with a Gamma distribution and logarithmic link to assess three predictors: (1) presence of conspecifics, (2) number of conspecifics, and (3) conspecific age class, testing against two response variables: nut-cracking behaviors occurrence rate and duration. Kruskal-Wallis tests assessed individual differences. Overall, our results indicate that nut-cracking behavior in adult capuchin monkeys is generally stable, even in the presence of conspecifics, suggesting that social context does not significantly affect performance. However, nut-cracking duration differed between two females during episodes involving conspecifics. We propose that individual and social factors interact to shape engagement in nutcracking, and that assessing the quality of social interactions during episodes may help clarify how individual characteristics and social dynamics jointly influence tool use.