Is passive observation of habituated animals truly passive?

Abstract

The term “habituated” is sometimes used to imply that animals no longer respond to the presence of a human observer. There is an accumulating body of evidence, however, suggesting that habituated animals that no longer perceive humans as a direct threat nevertheless continue to respond to their presence in other ways. Data were collected from a troop of free-ranging vervet monkeys in the Klein Karoo of South Africa for months 5–12 of their habituation period to determine how self-directed behaviour (SDB) was affected by human presence across time. SDB decreased across the 8 month period, indicating that habituation was ongoing. The human observer’s location in relation to the focal animal had a significant effect on SDB. Furthermore, when the habituation period was divided into an early and a late phase this pattern did not arise until the later habituation period (9–12 months). This evidence suggests that animals continue to respond to human presence as they become habituated, although the observed responses change.