Female bonnet macaques display aunting behavior to the extent that infants develop close attachment bonds with adult females other than their own mothers; loss of a mother does not greatly alter the behavior and physiology of infant bonnets, because they are generally adopted by other females (Reite and others 1989). In contrast, pigtail macaques (M. nemestrina) typically exhibit greater intragroup aggression and less social cohesion than bonnet macaques (Kaufman and Rosenblum 1967). Mothers are highly protective of their infants, restricting their activity to the extent that the infants do not form social bonds with other unrelated adults in the social group; loss of a mother can result in profound behavioral and physiological changes in infants (Reite and others 1981) and can have adverse long-term behavioral consequences (Capitanio and Reite 1984) and immunological consequences (Laudenslager and others 1986, 1996).

Even within a species, substantial individual differences in behavior can influence our interpretation of psychological well-being. Nonhuman primates are known to exhibit marked individual differences in "personality" (Caine and others 1983; Stevenson-Hinde and Zunz 1978; Suomi and Novak 1991). Macaques, for example, display relatively stable differences in temperament that have behavioral and physiological analogues. Both genetic mechanisms (Boccia and others 1994) and experience (Capitanio and others 1986) are probably involved.

A sudden change in the appearance or behavior of an animal might indicate a problem. For example, a shift from normal to unusual behavior might indicate a deterioration of the animal's well-being and warrant attention. Conversely, alterations of behavior in response to environmental manipulations (e.g., enrichment attempts) can be used to validate an intervention if undesirable behavior (e.g., self-biting) declines and normal behavior increases.

In summary, we expect animals in a state of psychological well-being to engage in species-typical behavior if given the opportunity to do so, to be capable of coping with minor disruptions in routine, and to display a balanced affect (as opposed to behavior that is indicative of chronic distress) and a behavioral repertoire that does not include maladaptive or pathological behavior. The best ways to fulfill such expectations are discussed in the next three chapters: programs to promote psychological well-being, general considerations of animal care, and special conditions related to research requirements.

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