A multi-stage anti-predator response increases information on predation risk.

Optimal escape theory generally assumes that animals have accurate information about predator distance and direction of approach. To what degree such information is available depends not only on the prey's sensory capabilities but also on its behaviour. The structure of behaviour can strongly constrain or support the gathering of information. The ability of animals to collect and process information is therefore an important factor shaping predator avoidance strategies. Fiddler crabs, like many prey animals, escape predators in a multi-step sequence. In their initial response, they do not have accurate information about a predator's distance and approach trajectory and are forced to base their response decision on incomplete information that is not strictly correlated with risk. We show here that fiddler crabs gather qualitatively different visual information during successive stages of their escape sequence. This suggests that multi-stage anti-predator behaviours serve not only to successively reduce risk but also to increase the quality of information with regards to the actual risk. There are countless reasons why prey animals are not able to accurately assess risk. By concentrating on sensory limitations, we can quantify such information deficits and investigate how improving risk assessment helps prey optimise the balance between predation risk and escape costs.