RESEARCH ARTICLE Hair Plucking, Stress, and Urinary Cortisol Among Captive Bonobos (Pan paniscus) Colin M. Brand, 1 * Klaree J. Boose, 1 Erica C. Squires, 1 Linda F. Marchant, 2 Frances J. White, 1 Audra Meinelt, 3 and J. Josh Snodgrass 1 1 Department of Anthropology, University of Oregon, Eugene, Oregon 2 Department of Anthropology, Miami University, Oxford, Ohio 3 Columbus Zoo and Aquarium, Columbus, Ohio 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 ¼ 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 ¼ 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 ¼ 0.88, P < 0.05) but not for males (r ¼0.73, P ¼ 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. © 2016 Wiley Periodicals, Inc. Keywords: undesirable behavior; glucocorticoid; trichotillomania INTRODUCTION Over the last several decades, endocrinology has become an invaluable tool in the study of both wild and captive animal populations. Hormonal data have been critical to supplementing behavioral observations and have been used extensively in understanding reproductive physiology and social behavior (e.g., Muller and Wrangham, 2004; Carlstead and Brown, 2005). Physiological markers, partic- ularly the glucocorticoid hormone cortisol, have also been used in captive studies as measures of psychosocial stress and overall well-being [M€ ostl and Palme, 2002]. Early research on physiological markers in non-human animals focused on domesticated taxa [for review see Palme, 2012]. The subsequent application of these techniques in zoo- housed animals has resulted in research conducted on many species including black rhinoceros [Carlstead and Brown, 2005], clouded leopard [Wielebnowski et al., 2002], polar bears [Shepherdson et al., 2013], and western lowland gorillas [Clark et al., 2012]. See Hill and Broom [2009] for review of this literature. While these biomarkers can be used in isolation, when used in conjunction with behavioral data they provide a more complete picture of particular behavioral patterns. Additionally, biomarkers such as cortisol can help explain the etiology of stereotypic behaviors such as pacing in captive polar bears [Shepherdson et al., 2013]. Grant sponsor: Rebecca Jeanne Andrew Memorial Award; grant sponsor: College of Arts and Science Dean’s Scholar Award, Miami University; grant sponsor: Nacey Maggioncalda Foundation; grant sponsor: University of Oregon.  Correspondence to: Colin M. Brand, Department of Anthropology, University of Oregon, 365 Condon Hall, 1218 Univeristy of Oregon, Eugene, OR 97403. E-mail: cbrand2@uoregon.edu Received 16 May 2016; Revised 30 June 2016; Accepted 04 August 2016 DOI: 10.1002/zoo.21320 Published online 17 August 2016 in Wiley Online Library (wileyonlinelibrary.com). © 2016 Wiley Periodicals, Inc. Zoo Biology 35: 415–422 (2016)