Prey pattern regularity and background complexity affect detectability of background-matching prey

We investigated how regularity of prey color pattern affects crypsis and how visual complexity of the background affects prey detection. We performed 2 predation experiments with artificial prey and backgrounds, using blue tits (Cyanistes caeruleus) as predators. In experiment 1, we found that contrary to a previous hypothesis, a pattern with repeated background-matching pattern element shapes was not easier to detect than a pattern with variable background-matching shapes. Increased background complexity with respect to shape diversity and complexity made prey detection more difficult. In experiment 2, we tested how spatial regularity of background-matching pattern elements affects crypsis. We found that spatially irregular prey with randomly placed pattern elements were harder to detect on both simple and complex backgrounds compared with spatially regular prey that had the elements aligned. Increased background element shape complexity made both prey categories harder to detect. In conclusion, our study shows that spatial regularity of prey pattern but not regularity due to invariable pattern element shapes deteriorates crypsis. Visually complex backgrounds and specifically those consisting of elements with complex shapes make detection of cryptic prey difficult.