Inanimate environmental enrichment for group-housed rhesus macaque infants.

The behavior of peer-reared infant rhesus macaques raised in enriched and nonenriched housing conditions was examined in order to evaluate the utility and effectiveness of object enrichment in a group housing setting. Environmental enrichment consisted of apparatuses designed to promote motor activity and to provide response-contingent feedback. Four animals in each condition were tested over a 14-month period. Behavioral observations were conducted in the home cage and during several test situations specifically designed to assess behavioral and affective responses to novelty and mild stressors. Monkeys in the enriched condition exhibited fewer behavioral and affective signs of disturbance than control infants in all observation conditions.

Reactions of nuclear-family-reared rhesus macaques to the births of younger siblings.

A group of juvenile rhesus macaques (Macaca mulatta) living in a nuclear-family laboratory environment was studied to determine their responses to the births of siblings. The frequencies of interactions with family members (mothers, fathers, and new siblings) and nonfamily (peers, unrelated infants, and unrelated adults) were studied over both the year preceding and the year following sibling birth. The frequencies of specific behaviors in each of those interactions and the frequencies of interactions in each area of the nuclear-family unit (home cage, play area, or other families' cage) were also examined. After new siblings arrived, several measures of interactions with mothers, fathers, and new siblings increased significantly; by contrast interactions with peers decreased substantially over the post-birth year. Although the frequency of interactions in home cages remained stable over the 2-year period, interactions outside of the subjects' home cages decreased significantly after siblings were born. An additional subject group whose mothers became pregnant but failed to deliver viable offspring showed no significant changes in total levels of interactions with peers; they did, however, exhibit increases in some interactions with unrelated infants and adults. Female juveniles interacted with new siblings significantly more often than did males when siblings were less than 6 months old, but as siblings grew older (6-12 months), females' levels of interaction with them fell to a level equal to that of males. In the nuclear-family social structure, the birth of a sibling resulted in an increased emphasis on family interactions at the expense of peer interactions.