ductive success (including reproductive behavior, fertility, prenatal adequacy, birth, and parental care) is often considered to be a good indicator of psychological well-being, but not all captive primates are of breeding age (they might be too young or too old), and some might be deliberately maintained in nonbreeding situations; furthermore, some types of reproductive failure (e.g., infertility) are not necessarily linked to poor psychological well-being. It could be argued that we should focus on searching for evidence of ill-being as represented by self-biting or bizarre, idiosyncratic activities, such as back-flips, eye-pokes, and hair-plucking. Although behavioral stereotypies might represent psychological disturbance brought about by environmental factors (Draper and Bernstein 1963), similar behavioral symptoms could result from atypical developmental processes and not be eliminated by manipulating housing. Nonhuman primates reared in deprived social environments during the first year of life often develop idiosyncratic behavior—such as rocking, self-clasping, and self-mouthing—as a replacement for maternal activities (Fritz 1986; Fritz and Howell, 1993a). Such patterns might persist for the life of the animal, and their appearance can reflect early rearing experience, rather than distress in the present environment (Mason and Berkson 1975). Some physical ailments can also be manifest in such symptoms as self-biting. Monkeys that develop reactive arthritis after shigella infections sometimes bite the affected limb, but in this case medical treatment will improve limb mobility and eliminate self-biting.
Thus it is extremely important to determine the etiology of atypical behavioral patterns before recommending any form of intervention. In some cases, medical treatment will be required; in others, environmental manipulations might be effective. Developmentally induced stereotypies are less amenable to treatment, but they can generally be avoided by rearing infant primates in a species-typical social environment. The severity of developmental abnormalities varies with the degree of early social deprivation. The most extensive data available come from rhesus monkeys (Macaca mulatta) and indicate that physical contact with social companions is essential for normal development (Mason 1991). If such contact is restricted to the mother alone or peers alone, some social deficits can persist for life (Mason 1991). Whereas limiting access to peers in a playroom situation seems to be less damaging than other forms of social restriction, the full range of species-typical behavior, including effective reproductive behavior, is more likely in animals given a sufficient amount of species-typical social experience. Only in a common enclosure can monkeys learn the consequences of their own actions on the behavior of social partners. It is that dimension of responsiveness that distinguishes social partners from inanimate objects.
When research protocols demand restrictions on early social experience, the institution should be prepared to deal with the long-term husbandry problems associated with such rearing practices. The atypical behavior exhibited by monkeys so restricted might reflect idiosyncratic devices to cope with early environmental deprivation, and in such cases direct intervention to disrupt the atypical