When to come out from a refuge: risk-sensitive and state-dependent decisions in an alpine lizard

Prey often respond to predator presence by increasing their use of refuges. However, unfavorable thermal conditions in refuges might entail physiological costs for an ectothermic prey. Thus, the decision of when to come out from a refuge should be optimized by considering the expected fitness effects of diminution of predation risk with time, but also by considering the cost of the loss of time spent at optimal body temperature maximizing physiological functions. The model of Ydenberg and Dill describes the trade-off between risk and cost for a prey fleeing to a refuge. We present a special case of this model to predict how emergence time from the refuge in lizards or other ectotherms should vary as a function of risk of predation and thermal costs of refuge use. The analyses of the variation in emergence time from a refuge of Lacerta monticola lizards in the field under two different predation risk levels supported the predictions of the model. As predicted, time spent in the refuge was longer when the threat of the initial attack had been higher, and therefore the subsequent diminution of risk was slower, but only when lizards emerged at the same place where they hid. When initial body temperature was high, some lizards decreased emergence time by emerging from a different place. In addition, the effects of thermal costs were more relevant in the high-risk situation. Time spent in the refuge under high risk increased when thermal conditions of the refuge were more similar to thermal conditions outside (i.e., physiological costs of refuge use were lower). We conclude that optimization of refuge-use strategies might help lizards cope with changes in predation risk without incurring excessive physiological costs.