Changes in nearest-neighbor associations in a captive group of western lowland gorillas after the introduction of five hand-reared infants

Abstract

The successful management of a captive gorilla population often necessitates the hand-rearing of infants and their subsequent re-integration into social groups of conspecifics. In the present study we quantified the changes in nearest-neighbor associations in a group consisting of a silverback male, three adult females, and two sub-adult females after the introduction of five hand-reared infants. Additionally, we examined the associations among kin and non-kin group members to determine whether genetic relatedness was a factor influencing the integration of the infants into the group and the subsequent patterns of association among infants and adults. Results showed that after the introduction, the silverback male spent >60% of his time in close proximity to an infant and 10% of his time within a “cluster” of infants. There was a significant change in a female's nearest-neighbor associations; however, the change did not include an infant. The most significant finding among infants was a strong bias by each to associate with another infant. When the infants associated with an adult, three of the five associated most with the silverback male (P < 0.001), whereas the other two infants distributed their time among all the adults. The most significant change in behavior patterns was exhibited by one of the sub-adult females who displayed parental behaviors 18% of the time compared to <1% for all other females. Adults and one sub-adult female associated significantly more often with related infants compared to unrelated infants (P < 0.025), and the infants showed a bias to associate with another related infant (P < 0.0001). Results of an infant's association with an adult showed that three of the five infants preferred to associate with a related adult (P < 0.0001). An individual's age, sex, and behavioral profile may have also influenced association patterns among group members. These findings lend strong support to the importance of peer groups and the presence of a silverback male for facilitating the integration of hand-reared infants into established adult groups. Zoo Biol 18:261–278, 1999. © 1999 Wiley-Liss, Inc.