Tool dimensions.

a) Tools provided to the chimpanzees during Experiment 1—those that they used as tools (Selected tools Exp 1) and those that they did not (Non-selected tools Exp 1); b) tools the chimpanzees obtained themselves from the natural vegetation of the island during Experiment 1 (Selected-non-provided tools Exp 1) and Experiment 2 (Selected-non-provided tools Exp 2). Diameters were not measured for these tools; c) Bamboo skewers (from the flags used to mark the presence of buried food) the chimpanzees used in Experiment 2 (Skewers Exp 2).