Intensive longitudinal behavior observations of male chimpanzees in stable mixed-sex social groups in a semi-natural environment were analyzed by state of development as defined by dental, growth and hormonal signals. Initial increase of sexual behaviors preceded adolescent hormonal changes. Peak prevalence of sexual behaviors coincided with the adolescent period. This period is also characterized by peak activity level and feeding. The major increase in aggression and stabilization of submissive behavior at adult level occurred concomitant with achievement of adult hormone levels and body size, and these were accompanied by increase of grooming affiliative behaviors.
The first 5 years of infant socialization was studied in two captive groups of chimpanzees. The infant’s frequency of social behaviors increased as it became older, the mother’s decreased, and that between mother and infant was relatively stable. The mother and infant socialized mostly with an age class similar to their own, with grooming and play being predominant, respectively. Their behaviors were more diverse when they socialized with a different age class. Initially, the mother and infant interacted more with females than males, but later more with males. The mother’s associations with juveniles and infants were high as her infant became more socially active with its peers. Most of the input to the mother-infant social relationship was by the mother.
ABSTRACT. Behavioral changes during weaning of chimpanzee infants in captive social groups were compared with those of infants in the natural habitat. Results of the weaning process were the same for the mother-infant pairs in captivity and the natural habitat, i.e., an infant independent of suckling, regular maternal transport and sleeping with the mother. The captive infants, however, did not respond to weaning with depression or regression to infantile behaviors as did infants in the natural habitat. Quite probably the social and physical environmental differences between the two habitats faciliated a less stressful weaning period for the captive mother-infant pairs.
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