Greater tool use diversity is associated with increased terrestriality in wild capuchin monkeys.

Abstract

Our goals were to (1) measure the terrestriality levels of a group of capuchin monkeys and (2) test the hypothesis that terrestriality has a positive effect on the stone tool use variability because the increased time on the ground would offer more opportunities to interact with the available stones, leading to more innovations of tool use behaviors. We predict a more diversified use of stone tools in the population with a higher degree of terrestriality. This study was on a group of capuchin monkeys (Sapajus libidinosus) at Serra da Capivara National Park (SCNP), Brazil. Scan sampling was done for 23 months, recording the behavior and substrate used by the individuals. The ground use rate was 41%, with no sex difference but an age difference: infants were less terrestrial than juveniles and adults. Compared to a population with a more limited tool use repertoire (Fazenda Boa Vista), SCNP adult capuchins are more terrestrial (43% v. 27%). Stone tool use diversity and terrestriality in capuchins appear to be positively correlated. Our results support this hypothesis and provide terrestriality measurements of the wild capuchin population with the most complex stone tool kit.