Nineteen hand-reared and seven mother-reared infant and juvenile gorillas were observed for a period of 3 years. Almost all hand-reared individuals developed stereotyped behaviors during the first months. In most cases these behaviors disappeared in the first or second year. Social behaviors, solitary play, nest building and grooming developed at about the same age in hand-reared and mother-reared infants. Hand-reared immatures showed significantly more solitary play, more aggression and less social play than mother-reared ones, especially when raised in pairs. When young gorillas were kept in groups, the frequencies of these behaviors came nearer to those of mother-reared immatures. No significant differences were noted in social play. When introduced to conspecifics, hand-reared infants sometimes reacted with indiscriminant aggression. Gorillas should thus preferably be reared in peer groups and be introduced to adults not later than one year of age.

Many zoo-born gorillas must still be hand-reared and sooner or later be associated with conspecifics in a breeding group. In this study the introduction and integration of 5 hand-reared infants at 3 zoos was observed for 2 to 4 years. Results showed that introductions proceed more smoothly if infants are first introduced to a calm and socially competent adult female. Infants should not be much older than I year at the start of integration, in order to allow for "adoption." Adopting females facilitate acceptance by the rest of the group. Problems frequently arise during introductions because of aggressiveness of silverbacks and the social incompetence of hand-reared individuals. Immature animals may react aggressively to the presence of adults, especially silverbacks, and thus delay the progress of integration. They should be introduced to adults as early as possible in order to facilitate the learning of essential social skills.

Though many zoo‐born gorilla infants still have to be hand‐reared and sooner or later associated with conspecifics, preferably a group, neither the managing procedures nor the process of social integration has been recorded in detail thus far. The present study, conducted at the Frankfurt Zoo, deals with a simultaneous introduction of two hand‐reared infants, a male and a female, into a group. The procedure of the introduction was documented. Behavioral observations were made during 1.5 years of integration by using ad libitum and focal‐animal sampling methods. The findings were compared with some data collected during a previous introduction conducted by a different procedure. The results show that both introductions were successful insofar as the infants were able to live within the group after a given time. But social integration by the new introduction procedure took much longer than previous attempts.

ABSTRACT. Studies of the behaviour of 26 (12 males and 14 females) captive infant and juvenile lowland gorillas showed clear sex differences. Females showed greater interest in young infants and were more active in nest building as well as in solitary and social grooming. Males were more active in locomotive, dominance, and aggressive behaviour and in social play. Hand-rearing further increased aggression. Males were more aggressive when they lived with only one partner, and they rose in rank even above older females, a pattern that has not been observed in naturally reared gorillas.