How size and conspicuousness affect the efficacy of flash coloration

Some prey are cryptic at rest but expose conspicuous colors when in motion. Previous findings suggest that these “flash displays” deceive would-be predators by providing false information about the color of prey, tricking them into continuing to look for prey with the conspicuous color when the prey have actually returned to their cryptic resting state. These results raise questions about the properties of flash coloration that make it effective. Here, using humans as visual foragers searching for artificial prey models on a computer screen, we tested whether the effectiveness of flash coloration depends on the size of artificial prey. In addition, we tested whether flashing a different, but inconspicuous, color other than the resting color of prey is sufficient to deceive predators, or whether the flash coloration actually needs to be conspicuous to elicit predator confusion. Results indicate that (i) flash coloration tends to be more effective in large prey and (ii) only conspicuous flash displays substantially reduce predation. Our findings help to explain why hidden color patches are more likely to be found in large insect species and why flash coloration is so often conspicuous. This study provides direct experimental evidence that the effectiveness of flash coloration is conditional, in that not all forms of flash display increase survivorship.