The behaviour of 48 chimpanzees (Pan troglodytes verus) was studied over 27 months in Liberia, West Africa. The chimpanzees were first studied while they were housed in groups in enclosures in a medical research institute, and then after their release onto a 9.7 ha offshore island. When the chimpanzees were observed in captivity, data on social behaviour were collected with the use of check sheets and ad libitum notes. Data were collected on aggression, social grooming, social play, sexual behaviour, and individual spacing. After release onto the island, data on both social and subsistence behaviour were collected with the use of ad libitum notes. Both changes in social behaviour and in the development of subsistence behaviour were observed following release of the chimpanzees onto the island. Rates of aggression decreased following release, whereas rates of social grooming increased. Rates of social play decreased overall, but this was due to a decrease in social play by adults. Stereotyped or abnormal behaviour shown by some subjects declined. Subsistence behaviours which were observed following release were foraging for naturally occurring foods (leaves, fruits, seeds, and nuts), ant-eating, and tool-use for nut-cracking. Some subjects were also seen building sleeping-nests in trees. The chimpanzees also split into subgroups (including consortships) which showed similar trends in size and composition to those observed in wild populations of chimpanzees. Some techniques found to be useful during the release process are discussed, and the study is compared to previous primate release projects.

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