Infant Development and General Social Behavior Among Captive Lowland Gorillas (Gorilla Gorilla Gorilla)

From September 1991 until April 1992, Melanie Cohen,\ud Christine Waanders and I conducted an observational study of the\ud gorilla group at the Philadelphia Zoo. There are 7 gorillas in the group including one fully adult male, age 24, and two adult females, also both age 24. The first female is the mother of a 6 year old male and an infant female. The second female is the other of a 7 year old male and a 3 \ud year old female. During the first half of the project, we became familiar with and took ad libitum observations on the group. During the second half of the\ud project, we observed the group systematically for a total of 35 hours. We observed the general group dynamics, the development of infant independence and patterns of play type and play partners among the immatures. Our results indicated that there is a high degree of cohesion among each of the matrilineal families within the larger group. The silverback male is with one of the families\ud more often than the other and prefers the adult female in the first family. The adult female of the second family appears to occupy an outgroup status in the group. This is evident by the general distance between her and the other animals and the aggression targeted at her. The infant in this \ud group is responsible for\ud maintaining both proximity and distance from her mother. As she\ud matures, she becomes more active and engages in less object play and increasingly more climbing and swinging. The older immatures engage in interactive play more often than solitary play, while\ud he younger immatures engage in solitary play more often than interactive play. Within immature interactive play, sex, age and\ud kinship influence the choice of play partners. The infant's in­teractive play is most often with her 3 year old half sister. The two immature males, ages 6 and 7, \ud play most frequently with each other. The second playmate for each of them is the 3 year old female. The 3 year old's brother, however, plays with her more frequently than the other immature male. This study suggests that development and general social dynamics are not very different in captivity than they are in the wild