Token transfer between mother and offspring chimpanzees (Pan troglodytes): mother–offspring interaction in a competitive situation
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Chimpanzees can flexibly use tokens in cognitive tasks, but it is still unknown if they can share and/or compete over tokens as they do for food. This study aimed to evaluate the interactions spontaneously occurring between mother and offspring chimpanzees when tokens exchangeable for food were provided. Forty tokens were scattered on the floor in an experimental playroom. Three mother and offspring chimpanzee pairs were tested. Each token was exchangeable for a piece of food in a vending machine installed on the wall of the playroom. In the beginning of the study, both mother and offspring took tokens and exchanged them for pieces of food independently. Later, two offspring started to take more tokens than their mothers. At that time, the offspring whimpered or cried more often than during earlier sessions. This behavior compelled the mothers to abstain from taking tokens. The mothers sometimes shared their tokens with their offspring, or were tolerant of their offspring taking their tokens from their hand. For one pair, the offspring sometimes shared tokens with her mother when her mother begged for the tokens. These results suggest that chimpanzees’ cognitive abilities enable them not only to use tokens, but also to compete for tokens, as they do for food. The results also suggest that token sharing between mother and offspring may be bidirectional and that transfer of tokens mainly occurs as a result of begging, although on some occasion offspring were able to obtain a token directly from his/her mother through tolerated scrounging.
KeywordsMother–offspring pair Chimpanzees Sharing Token transfer Vocalization
The first author has now moved to Wildlife Research Center, Kyoto University. This study was financially supported by the MEXT Grants-in-Aid for Scientific Research (Nos. 16002001, 19530653, 20002001), the Global COE Program “Evolution and Biodiversity” and “Revitalizing Education for Dynamic Hearts and Minds”. We wish to thank Dr T. Humle for her reading and comments on the draft of this manuscript and the laboratory staff members for their assistance. We also thank the staff members of the Center for Human Evolution Modeling Research, Primate Research Institute, Kyoto University for the management of the subjects’ health.
Supplementary material S1 shows the first token transfer in the Ai-Ayumu pair from the beginning of the session until Ayumu approaches to the vending machine with tokens given to him by Ai. (WMV 22240 kb)
Supplementary material S2 shows that Ai transferring a token to Ayumu Ayumu was cryingin response to his crying behavior when whilst Ai was is exchanging tokens with for food. Ayumu continued continues to crying until , and finally Ai moves away from the vending machine and approached approaches to Ayumu. (WMV 7800 kb)
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