Hair plucking, stress, and urinary cortisol among captive bonobos (Pan paniscus)

Abstract

Hair plucking has been observed in many captive primate species, including the great apes; however, the etiology of this behavioral pattern is poorly understood. While this behavior has not been reported in wild apes, an ethologically identical behavior in humans, known as trichotillomania, is linked to chronic psychosocial stress and is a predominantly female disorder. This study examines hair plucking (defined here as a rapid jerking away of the hair shaft and follicle by the hand or mouth, often accompanied by inspection and consumption of the hair shaft and follicle) in a captive group of bonobos (N = 13) at the Columbus Zoo and Aquarium in Columbus, Ohio. Plucking data were collected using behavior and all-occurrence sampling; 1,450 social and self-directed grooming bouts were recorded during 128 hr of observation. Twenty-one percent of all grooming bouts involved at least one instance of plucking. Urine samples (N = 55) were collected and analyzed for the stress hormone cortisol. Analyses of urinary cortisol levels showed a significant positive correlation between mean cortisol and self-directed plucking for females (r = 0.88, P < 0.05) but not for males (r = -0.73, P = 0.09). These results demonstrate an association between relative self-directed hair plucking and cortisol among female bonobos. This is the first study to investigate the relationship between hair plucking and cortisol among apes. Overall, these data add to our knowledge of a contemporary issue in captive ape management. Zoo Biol. 35:415-422, 2016. © Wiley Periodicals, Inc.

What animals do not do or fail to find: A novel observational approach for studying cognition in the wild

“…Moreover, wild animals are less likely to endure uncontrollable stress that is known to result in aberrant behaviors and signs of depression in many captive animals . Enrichment conditions have improved substantially over the years, and most experiments are conducted on a voluntary basis.…”

“…Moreover, wild animals are less likely to endure uncontrollable stress that is known to result in aberrant behaviors and signs of depression in many captive animals. [100][101][102][103][104] Enrichment conditions have improved substantially over the years, and most experiments are conducted on a voluntary basis. Yet animals that are most often subject to cognitive tests, such as primates, cetaceans, corvids, and elephants are all long-lived animals, [105][106][107][108] and a history of uncontrollable stress, including social and nutritional stress and unnatural rearing conditions (e.g., not being reared by the mother) can have long-term effects on brain morphology.…”

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

“…Thus, rearing may not consistently explain the presence or absence of this behavioral pattern. In a related study, Brand et al () investigated the etiology of hair plucking in the same group of bonobos reported on in the Brand and Marchant () paper. Urinary cortisol levels showed a significant positive correlation between mean cortisol and self‐directed plucking for females ( r = 0.88, P < 0.05) but not for males ( r = −0.73, P = 0.09).…”

“…This suggests multiple etiologies for hair plucking: Some individuals, particularly females, may hair pluck themselves in response to stress, whereas stress did not explain self‐directed hair plucking in males. Thus, hair plucking may manifest for reasons other than stress in captive bonobos, including social transmission (Brand et al, ).…”

“…It seemed useful to investigate more widely the patterns of hair plucking among bonobos. We chose to differentiate between self‐directed and social hair plucking given the potential functional differences (see Brand et al, ). The study reported here had three objectives.…”