Characterization of Stone Tool Use in Wild Groups of Critically Endangered Yellow‐Breasted Capuchin Monkeys (<i>Sapajus xanthosternos</i>)

Sapajus xanthosternos displayed tool use patterns very similar to those of S. libidinosus. The main difference was in regards to physical force; in our study, the mean weight of stones used by S. xanthosternos was higher than the mean reported for S. libidinosus at most field sites; however, there was no difference in hammer weight between S. libidinosus and S. xanthosternos when hammering Macaúba. We also registered the heaviest hammer stone for tool use (7.675 kg) known for the robust capuchin genus. It is clear from our study that tool use capacity and characteristics are conserved across the radiation of extant Sapajus, suggesting a possible stone tool use cognitive capacity spanning up to 3.3 million years of diversification within this genus. Unlike stone tool use occurring throughout the year for S. libidinosus, at our study sites S. xanthosternos used nutcracking tools only during the dry season.