Psychological well-being refers to mental state. It cannot be defined in terms of the environment, although environments certainly influence individual well-being. It cannot be equated with an activity or behavioral profile, although individual status influences behavior. It is not synonymous with any physiological state, although physiological condition and psychological well-being interact. Psychological well-being is influenced by meeting the needs of an individual animal that are based on its species, sex, age, and developmental experiences. Its assessment must be based on multiple indexes:
- The animal's ability to cope effectively with day-to-day changes in its social and physical environment (with reference to meeting its own needs).
- The animal's ability to engage in beneficial species-typical activities.
- The absence of maladaptive or pathological behavior that results in self-injury or other undesirable consequences (see Bayne 1996 for a discussion of the normal and abnormal behaviors).
- The presence of a balanced temperament (appropriate balance of aggression and passivity) and absence of chronic signs of distress as indexed by the presence of affiliative versus distress vocalizations, facial expressions, postures, and physiological responses (e.g., labored breathing, excessive cardiac response, and abnormal hormonal concentrations).
The assessment should be based on the behavior of an individual animal and not simply on normative physical and behavioral profiles of the species. Although behavior that deviates from species-typical patterns warrants further exploration, the expression of atypical behavior in an animal might not be suffi-
cient evidence to infer a serious detriment in psychological well-being. The first sign of any abnormality is often a change in behavior. If the atypical behavior of an animal can be attributed to its age and sex, the behavior might be persistent and acceptable for that animal. Whereas it might be argued that rearing conditions and treatments that lead to atypical behavioral profiles should be avoided as undesirable, animals already reared under such conditions can be maintained in ways that are supportive of their individual psychological well-being as an amelioration of unusual behavior patterns caused by their earlier life experiences.
Assessment of psychological well-being should be based on the factors listed above. For example, the brief occurrence of symptoms associated with stress is not evidence of a chronic state of distress. The entrance of an unfamiliar person into an animal colony room might provoke expressions of acute fear from animals that do not ordinarily exhibit such symptoms. Furthermore, the absence of all environmental stressors is not required to prevent distress; in fact, the elicitation of normal effective coping responses to the minor stressors of life can be beneficial.
Nevertheless, in the assessment of a program designed to provide for the psychological well-being of nonhuman primates, all recognizable instances of behavior and physiology that deviate from the species normative pattern warrant further inquiry. Such instances should be noted, and colony records should indicate that an appropriately trained person offered a provisional diagnosis and instructions for disposition of the case. Once an appropriate person has assumed responsibility for remediation or has prescribed for the psychological well-being of the animals in question, this should be regarded as an appropriate clinical response.
A well-designed plan to provide for the psychological well-being of nonhuman primates must also provide for their physical well-being. Providing for psychological well-being, however, might require some compromise with standards for maximizing sanitation and isolating individual animals from all sources of potential contaminants. Beyond reasonable physical well-being, psychological well-being is enhanced by
- Appropriate social companionship.
- Opportunities to engage in behavior related to foraging, exploration, and other activities appropriate to the species, age, sex, and condition of the animal.
- Housing that provides for suitable postural and locomotor expression.
- Interactions with personnel that are generally positive and not a source of unnecessary stress.
Absolute standards or minimums are neither possible nor desirable for each of those four characteristics, because of the great variability of each animal's previous history and needs and the variability among the institutions holding them. No single solution will always be best, and at present the research required
to substantiate recommendations is still in the future. We know that the needed social companionship depends on species, age, sex, and rearing history and ranges from sensory contact to direct association with multiple other animals. We know that the utility of devices designed to provide opportunities for foraging and exploration depends on the same variables. We know that housing requirements depend on bodily dimensions, normal postures, and locomotor patterns (e.g., arm swinging versus bipedal leaping versus quadrupedal striding or climbing). We know that some animals rarely tolerate close human contacts, whereas others seem to respond positively to familiar humans. Quantitative specification of minimums for each characteristic might be considered desirable by some, but it is important that standards be validated against performance; that is, do the specified characteristics actually improve the psychological well-being of the affected animals?
Nevertheless, a comprehensive program to improve the psychological well-being of nonhuman primates will attend to each of the variables and include a means to test and assess the influence of each. The benefits of providing a cage companion, an enrichment device, a cage of design and dimensions that appeal to a human's aesthetic sense, and a sensitive caregiver to interact with the animals should be validated and documented. A performance standard should be used to show whether the provided features increase the diversity and amount of normal behavior and decrease the frequency and duration of behavior that results in self-injury or other undesirable consequences. Social companions must be conducive to positive affiliation rather than be a source of stress and a cause of avoidance; an inappropriate companion can be worse than no companion at all. Enrichment devices do their job when they provide otherwise-absent opportunities to engage in species-typical foraging and exploratory activities, but a device that requires excessive time for foraging at the expense of social or other species-typical activities is not an enrichment. Likewise, enrichment devices can be used by multiple animals, but they should not become a source of competitive conflicts. Cage dimensions and furnishings are suitable if they allow for expression of normal postures and locomotor expression, as opposed to open unused spaces and furnishings that do not allow for normal postural positions. Human interactions should provide for activities that the animals appreciate, rather than simply provoke animal activity.
The four bulleted items listed above are related. Whereas spatial requirements are based on individual needs, social housing need not mean that spatial requirements for one animal are multiplied by the number of animals housed. If housing provides sufficient space for one animal to express a normal locomotor pattern, a second animal has access to the same space for locomotor expression minus only the volume of space actually occupied by the first animal. For example, if housing needs to be 2 m high to provide sufficient vertical space for an animal's postural and locomotor needs, two animals do not need vertical space 4 m high. Floor areas likewise need not be simple multiples; in fact, for arboreal
animals that normally flee upward and spend much of their locomotor time climbing, floor areas might be secondary to vertical space in providing for postural and locomotor expression. The volume of space available, rather than floor area, might be critical for nonhuman primates. Guidelines for minimal space for primates should be reassessed on the basis of such considerations (NRC 1996).
Whereas we know some of the relevant dimensions that influence psychological well-being in nonhuman primates and some of the outcomes that we hope to attain by proper specification of such characteristics, we cannot specify the exact measurements required for each of the many species and for individual animals of every age, sex, and life history. But we can expect institutions to monitor and assess the conditions of animals in their charge and to make appropriate efforts to improve conditions that do not meet the criteria of psychological well-being.
In sum, whereas a great deal is known about the natural history and behavior of nonhuman primates held in captivity, much more information is required. While some research areas are discussed in Chapter 10, the use to which this information is to be put should be unequivocal—the furtherance of performance goals through the enhancement of knowledge. Even with substantially greater information, the development of prescriptive recipes for primate well-being would not be desirable. A variety of solutions might achieve the same general goal: animals that are maintained under conditions that promote their physical and psychological well-being. The aim of research in this area should be to find means by which to assess psychological and physical well-being and to provide the knowledge necessary to develop programs to achieve this general goal. Animals maintained for research, exhibition, or education can all be maintained under conditions that are consistent with this goal and that will provide for their well-being. It is the responsibility of all who keep nonhuman primates to ensure that personnel are appropriately trained to develop procedures consistent with the goals of the institution and the psychological and physical well-being of the animals in their charge.