Performance of the keas across Experiments 2–5.

Trials (errors) show the total number of trials needed and errors made to reach criterion on the training stage of the delay experiment (Experiment 2). Randomized delay 0–65 secs and 26–65 secs show the number of successful trials keas completed at test in Experiment 2, both for all trials, and for trials longer than keas had previously experienced during training. Solo-Duo indicates the number of successful trials in Experiment 3, No Rope shows the same for Experiment 4, Prosocial Motivation shows the same for (Experiment 5 p