About the article of visitor effect on primates. In modern zoos, where monkeys are rarely teased or fed, it often seems to me that it is primate social structure which is most important, and interaction with visitors is result not the cause. Small groups and lone animals are more likely to approach people. A large, well adjusted group is mostly occupied by themselves. Also, male monkeys seem to treat visitors (and staff) as rivals, venting their aggression especially if there are no other males.