Effects of hand-rearing on the behavioral development of infant and juvenile gorillas (Gorilla g. gorilla).

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.