Overstaying in patchy foraging can be explained by behavioral variability

Foragers often systematically deviate from rate-maximizing choices in two ways: in accuracy and precision. That is, they both use suboptimal threshold values and show variability in their application of those thresholds. We hypothesized that these biases are related and, more specifically, that foragers’ widely known accuracy bias – over-staying – could be explained, at least in part, by their precision bias. To test this hypothesis, we analyzed choices made by three rhesus macaques in a computerized patch foraging task. Confirming previously observed findings, we find high levels of variability. We then show, through simulations, that this variability changes optimal thresholds, meaning that a forager aware of its own variability should increase its leaving threshold (i.e., over-stay) to increase performance. All subjects showed thresholds that were biased in the predicted direction. These results indicate that over-staying in patches may reflect, in part, an adaptation to behavioral variability.