The resourceful chimp even manufactures concrete "missile" discs, made from loose materials in structures on his "chimpanzee island" home.
Antonio Moura, who conducted research while in the Department of Biological Anthropology at the University of Cambridge, observed capuchin monkeys at Serra da Capivara National Park in Brazil. Moura noticed that whenever he approached, the monkeys would move to higher ground and search for a loose stone, which they would then hit on a rock surface several times. The resulting noise, presumably, was meant to keep people like Moura away.
A new study, accepted for publication in the December issue of General and Comparative Endocrinology, suggests that stress levels of captive primates do widely vary, but not necessarily because of humans. The stress hormone cortisol, found in easily gathered hair and fecal samples, reveals chimp anxiety.
Yumi Yamanashi of Kyoto University and colleagues determined that how the chimps related to each other contributed, or not, to stress levels. For example, in one chimp group, Yamanashi and team found that "the individual with the highest hair cortisol level was one of the two individuals introduced into the group a year before the study." In other words, he was the new chimp in town.