EXCHANGE OF OBJECTS BETWEEN HUMANS AND CAPTIVE WESTERN LOWLAND GORILLAS

An experiment was carried out to assess the ability of captive western lowland gorillas (Gorilla g. gorilla) to exchange objects with a huma n partner. Before the exchange itself, individuals had to learn to giv e an item to the experimenter. Four individuals out of nine performed active giving. After that familiarization with giving behaviour, two k inds of exchanges, of increasing complexity, were tested with gorillas . Simple exchange (give C to obtain D) was the first procedure and six gorillas out of nine succeeded. Double exchange (give B to receive C, then give back C to obtain D) was performed only by three individuals and triple exchange (give A to receive B, give back B to receive C, t hen give back C to obtain D) was performed only by two individuals. Di fferent types of errors were scored, as well as social constraints on learning. Results showed that (1) naive gorillas are able to geta rewa rd (D) in an experimental exchange situation; and (2) the complex rule s of multiple successive exchanges were not easily understood by goril las.