Decades of research shows that housing highly intelligent, social primates alone causes them extensive psychological and physical harm. One study documented that as many as 89 percent of singly-housed monkeys exhibit abnormal, stress-induced behaviors including incessant pacing, rocking, hair-pulling and even self-biting. They also suffer from higher incidence of physical ailments like heart disease. And yet, a recent survey based on self-reports from research institutions determined that 16 percent of primates in U.S. laboratories are singly housed (Bennett, 2016). The study reported that 10,572 primates in the survey respondents’ laboratories were housed alone with no opportunities for tactile contact with other primates, while an additional 3,384 primates were housed alone with limited contact with other primates. This is clearly unacceptable and all efforts must be taken to socially house nonhuman primates. Fundamentally, this means that laboratories must understand that if a primate is housed in a cage by herself—even if she is able to see, hear, and smell other primates—she is still singly housed and will be vulnerable to the myriad psychological and physiological deficits that have been thoroughly documented in the scientific literature.
Bennett, B. T. (2016). Association of Primate Veterinarians 2014 Nonhuman Primate Housing Survey. Journal of the American Association for Laboratory Animal Science, 55(2), 172-174.