Countershading enhances cryptic protection: an experiment with wild birds and artificial prey

Of the many traits seen in cryptic prey animals, countershading (darker pigmentation on those surfaces exposed to the most lighting) is one of the commonest, and paradoxically one of the least understood. Countershading has been hypothesized to enhance crypsis by shadow-obliteration, in which lighter coloration on the undersides compensates for increased shadow in these regions, thus reducing detection by visually hunting predators. We tested the hypothesis that countershading enhances crypsis in two experiments with artificial prey presented to free-living birds. In the first experiment, artificial prey were presented on lawns to a range of bird species. In the second experiment, the prey were presented on green boards to individual blackbirds, Turdus merula. In both experiments countershaded prey had significantly lower levels of predation than controls. Our results show that countershading can enhance cryptic protection and has important implications for the evolutionary ecology of prey defences.