Token transfer between mother and offspring chimpanzees (Pan troglodytes): mother-offspring interaction in a competitive situation

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.