Strategic decision-making by chimpanzees in a Snowdrift-Game (#887)
Chimpanzees must be able to coordinate with others even when conflicts of interest are present (e.g. cooperative hunting). The “Snowdrift-Game” has been proposed as a model to understand how organisms coordinate and make decisions under conflict situations. By investigating whether and how chimpanzees solve these dilemmas we can gain insight into the mechanisms of cooperation.
We presented pairs of chimpanzees with two different Snowdrift games. In Experiment 1 subjects could provide equal food rewards to themselves and a partner by pulling a weighted tray in high and low weight trials either by pulling simultaneously and share the load or free-riding (letting a partner pull ), with the risk that if both tried to free-ride the food was lost. In Experiment 2 subjects were faced with an unequal reward distribution paradigm. Similarly to Experiment 1, in the critical condition the higher reward was acquired by letting a partner act with the risk that if neither acted the rewards would be lost.
In both experiments chimpanzees were highly successful at solving the dilemma. They almost never lost the rewards because at least one partner was willing to pay the cost (increased effort in Experiment 1 or decreased rewards in Experiment 2) to avoid coordination failure (no reward). In Experiment 1 chimpanzees solved the game by pulling together in 70% of trials. They were more likely to cooperate in high cost (high weight) condition, but cooperation in this situation was also likely to be more unequal (one partner invested more effort). In Experiment 2, subjects waited longer for their partner to act when this would lead to a higher reward.
These results suggest that chimpanzees strategically adjust their timing and actions to maximize their payoffs while maintaining successful coordination.