Stochastic choice drives variability in patch foraging decisions across species

Staying to exploit remaining resources or leaving to seek better options elsewhere is a fundamental decision across species. Optimal patch foraging theories propose deterministic rules for when to leave a depleting resource but real foragers show considerable variability in when they leave. Here we show that foragers making a stochastic choice of when to leave a patch is sufficient to explain their variability across tasks and species. We also show stochastic choice makes two unintuitive predictions, which we validate in our data. First, under a wide range of conditions, stochastic choice makes foragers' leaving variability independent of the rewards available in the environment. Second, that foragers use a suboptimal internal model for setting their choice stochasticity from their environment's average reward rate. Our findings suggest stochastic choice is an underappreciated but powerful contributor to foraging decisions.