Flicker is part of a multi-cue response criterion in fiddler crab predator avoidance

Predator avoidance behaviour costs time, energy and opportunities, and prey animals need to balance these costs with the risk of predation. The decisions necessary to strike this balance are often based on information that is inherently imperfect and incomplete because of the limited sensory capabilities of prey animals. Our knowledge, however, about how prey animals solve the challenging task of restricting their responses to the most dangerous stimuli in their environment is very limited. Using dummy predators, we examined the contribution of visual flicker to the predator avoidance response of the fiddler crab Uca vomeris. The results illustrate that crabs let purely black or purely white dummies approach significantly closer than black-and-white flickering dummies. We show that this effect complements other factors that modulate escape timing such as retinal speed and the crab's distance to its burrow, and is therefore not due exclusively to an earlier detection of the flickering signal. By combining and adjusting a range of imperfect response criteria in a way that relates to actual threats in their natural environment, prey animals may be able to measure risk and adjust their responses more efficiently, even under difficult or noisy sensory conditions.