When to run from an ambush predator: balancing crypsis benefits with costs of fleeing in lizards

Many studies show that prey should not flee immediately from approaching predators, but should adjust their fleeing distance to minimize flight costs. We explored a new scenario where an ambush predator appears close to a relatively cryptic prey, that the predator has not yet detected. Then, instead of approaching further, the predator stops and starts looking for prey from a vantage point, while maintaining a constant distance with the still undetected prey. Probability of detection of prey will increase with time of searching. We predicted that prey should wait before escaping until the time (‘fleeing time’) when the risk of being detected, which depends on prey conspicuousness, equals fleeing costs. We tested this prediction in the field by simulating an ambush predator and examining escape decisions of rock lizards, Iberolacerta cyreni, considering two risk levels (i.e. the predator has or does not have information on the prey location) and relative conspicuousness of lizards (i.e. differences in coloration and body size). Lizards fled after some time, even if the distance between predator and prey remained constant and an attack had not been launched, probably because risk of being detected increases with time. However, to minimize fleeing costs, lizards modulated their fleeing times depending on probability of being detected (related to colour conspicuousness differences) and on size-dependent escape performance. Nevertheless, conspicuousness seemed unimportant after the predator had acquired information on the location of a prey, and/or the predator was considered as more dangerous because it had previously attacked the prey.