Lutz, C. K., Davis, E. J., Suomi, S. J. et al. 2007. The expression of self-injurious behavior in Macaca mulatta: prevalence, risk factors, and context. American Journal of Primatology 69(S1), 38. (30th Meeting of the American Society of Primatologists Scientific Program, Abstract #18)

Self-injurious behavior (SIB) such as self-biting and self-wounding has been observed in a small, but persistent, percentage of captive nonhuman primates. Although biting often looks severe, not all self-biters wound themselves. Risk factors for SIB in rhesus macaques were investigated and include an animal’s age as well as sex. Even though there was no age difference in self-biting, animals that wounded tended to be older. In singly-housed animals, more males than females exhibited self-biting and self-wounding. However, in a colony of group-housed animals, a sex difference in biting was not observed and self-inflicted wounding was not reported for either sex. Environmental factors such as single housing at an early age or for an extended period of time increased the likelihood of both self-biting and wounding, and minor veterinary procedures such as blood draws increased the likelihood of wounding. Although SIB has been referred to as a form of self-aggression, stress, rather than aggression per se, has been shown to play a role. When levels of stress were held constant, self-biting was independent of social aggression. However, self-biting can occur with no obvious precipitating trigger or change in salivary cortisol, suggesting that either biting also occurs in the absence of stress, or biting helps to reduce stress.