Observer effects in a remote population of large-headed capuchins, Sapajus macrocephalus

Human observers often are present when researchers record animal behavior, which can create observer effects. These effects are rarely explicitly investigated, often due to the assumption that the study animal is habituated to or unaffected by a human’s presence. We investigated the effect of human pressure gradients on a remote population of large-headed capuchins, Sapajus macrocephalus, looking specifically at the effects of number of observers, distance to observers, and distance to the research base. We conducted this study over 4 months in the Pacaya-Samiria Nature Reserve, Peru, and collected 199 two-minute focal samples of capuchin behavior. We found that capuchin monkeys fed less when human observers were closer to the focal individual, when more observers were present, and when capuchins were closer to the research base. We found no other consistent differences in capuchin monkey behavior across the measured human pressure gradients, although capuchins directed a high proportion of their vigilance toward humans (29% in adults and 47% in infants). Our results support the hypothesis that human pressure gradients influence animal behavior. Given the proportion of human directed vigilance, we recommend that all studies that use human observers to record animal behavior consider human-directed vigilance, record the number of observers, as well as the observer-focal animal distance, to check for these effects.

Monkey Mountain as a Megazoo: Analyzing the Naturalistic Claims of "Wild Monkey Parks" in Japan

In Japan, yaen kōen or "wild monkey parks" are popular visitor attractions that show free-ranging monkey troops to the paying public. Unlike zoos, which display nonhuman animals through confinement, monkey parks control the movements of the monkeys through provisioning. The parks project an image of themselves as "natural zoos," claiming to practice a more authentic form of displaying animals-in-the-wild than that practiced by the zoo. This article critically evaluates the monkey park's claim by examining park management of the monkeys. The article shows the monkey park's claim to display wild monkeys to be questionable because of the way that provisioning changes monkey behavior. Against the background of human encroachment onto the forest habitat of the monkey, the long-term effect of provisioning is to sedentarize nomadic monkey animals and to turn the wild monkey park into a megazoo.