Prevalence and characteristics of hair plucking in captive bonobos (Pan paniscus) in North American zoos.

When primates exhibit hair loss and are observed to engage in self or social hair plucking (a rapid jerking away of the hair shaft and follicle by the hand or mouth, often accompanied by inspection, and consumption) the altered appearance, and behavior patterns are thought to reflect individual physiological, and psychological well-being. Hair loss and hair plucking occur in many captive primate species, including all of the great apes. We present the first survey of this behavior among captive bonobos (N = 88; 50 females and 38 males) in seven zoos in the United States. We found that 43% of the population engaged in this behavior pattern and discounting youngsters (who are not observed to hair pluck until the age of five), 58% of individuals hair plucked. Of the individuals who hair plucked, 97% engaged in social plucking, whereas 46% engaged in self-directed plucking. We regressed the occurrence of hair plucking with multiple predictor variables using binary logistic regression and multimodel inference to determine which predictors best explained the prevalence of self-directed and social plucking. We also analyzed publicly available data on hair plucking in captive chimpanzees. We found that the occurrence of another abnormal behavior, age, origin, and pelage condition best explained self-directed plucking in bonobos. Social plucking was explained by age, origin, pelage, and sex. Our analysis of chimpanzee hair plucking revealed that plucking is strongly influenced by rearing and sex. This study demonstrates that hair plucking is more prevalent in captive bonobos compared to captive chimpanzees and gorillas, however, the covariates associated with hair plucking for each species are different. Our data suggest a potential link between self-directed plucking and well-being. However, the higher prevalence and etiology of social hair plucking is more difficult to explain.