Pituitary-adrenal response in mother and infant squirrel monkeys following brief separation was assessed. Each mother and infant pair was tested under each of 3 conditions: (1) Basal; (2) Separation-Reunion; and (3) Separation. Samples were obtained from mothers and infants in the Separation and Separation-Reunion conditions 30 min following the initial disturbance. A similar paradigm was used to assess the effects of separation in surrogate-reared animals. The results indicate that mothers, infants, and surrogate-reared infants respond to 30-min separation with a substantial increase in plasma cortisol. The values obtained in the Separation-Reunion condition did not differ significantly from Basal values in any of the 3 groups, suggesting that the effect of separation on the pituitary-adrenal system is not due to the disturbance involved in the separation procedure. The response of surrogate-reared infants suggests that these infants develop similar attachments to the surrogate as normal infants to their own mothers.

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The effects of 30-min separation from peers on behavior and plasma cortisol levels were studied in juvenile, mother-reared, female squirrel monkeys, housed in triads. Juveniles vocalized much more frequently when isolated in a novel room than they did when either undisturbed, handled only, placed with both peers in a novel room, or separated from one peer and housed with the other in the home cage. When separated from one peer in the home cage, the monkeys engaged in putative scent-marking behaviors more frequently than when undisturbed. Exposure to the novel room resulted in increased vocalizing, and decreased locomotor activity and scent marking, regardless of whether the subject was isolated or with peers. Plasma cortisol levels were elevated following all manipulations and no effects could be attributed specifically to separation or exposure to novelty. These results demonstrate that brief separation from peers can evoke a behavioral reaction in juvenile squirrel monkeys that resembles the behavioral "protest" response of maternally-separated infants, and that the response of juveniles, like that of infants, varies greatly with the separation procedure employed.Key words: peer separation, juveniles, protest behavior, cortisol, squirrel monkey INTRODUCTIONIn the study of primate social relationships, the strength of a relationship often is assessed by examining the seventy of disturbance that is caused by its disruption. This technique has most often been used to investigate the bond between mother and infant macaques [Mineka & Suomi, 19781. Following maternal separation, infants show an initial stage of behavioral activation or "protest" characterized by increases in such behaviors as vocalizations and locomotor activity [Jensen & Tolman, 1962; Kaplan, 19701. In some macaque species, protest is followed in several days by a "despair"reaction distinguished by inactivity and social withdrawal [Seay et al., 1962; Kaufman & Rosenblum, 19671. These behavioral stages are paralleled by physiological changes including alterations in heart rate, body temperature, and sleep patterns Reite et al., 1978al. Infant macaques reared on maternal surrogates exhibit behavioral and physiological disturbance following separation from the surrogate, although the ef- 144Hennessy, Mendoza, and Kaplan fects are less severe. This suggests that the attachment of the infant macaque to its surrogate is less intense than is that of infant to mother [Reite et al., 1978b; Meyer et d., 19751. Young rhesus macaques raised in peer groups without maternal contact display protest and despair following peer separation similar to that seen following separation from the mother [Suomi et al., 1970,19761. On the other hand, in juvenile peer groups formed following weaning from the mother, peer separation has been found to induce a protest reaction, but no apparent signs of despair [Bowden & McKinney, 1972;Erwin et al., 1971 Erwin et al., ,1973 McKinney et al., 19721. These data suggest that young rhesus form relationships with peers that ar...