Outline and surface disruption in animal camouflage.

Camouflage is an important strategy in animals to prevent predation. This includes disruptive coloration, where high-contrast markings placed at an animal's edge break up the true body shape. Successful disruption may also involve non-marginal markings found away from the body outline that create 'false edges' more salient than the true body form ('surface disruption'). However, previous work has focused on breaking up the true body outline, not on surface disruption. Furthermore, while high contrast may enhance disruption, it is untested where on the body different contrasts should be placed for maximum effect. We used artificial prey presented to wild avian predators in the field, to determine the effectiveness of surface disruption, and of different luminance contrast placed in different prey locations. Disruptive coloration was no more effective when comprising high luminance contrast per se, but its effectiveness was dramatically increased with high-contrast markings placed away from the body outline, creating effective surface disruption. A model of avian visual edge processing showed that surface disruption does not make object detection more difficult simply by creating false edges away from the true body outline, but its effect may also be based on a different visual mechanism. Our study has implications for whether animals can combine disruptive coloration with other 'conspicuous' signalling strategies.

Testing Thayer's hypothesis: can camouflage work by distraction?

One of the oldest theories of animal camouflage predicts that apparently conspicuous markings enhance concealment. Such 'distraction' marks are hypothesized to work by drawing the viewer's attention away from salient features, such as the body outline, that would otherwise reveal the animal. If distraction marks enhance concealment, then they offer a route for animals to combine camouflage markings with conspicuous signalling strategies, such as warning signals. However, the theory has never been tested and remains controversial. By using camouflaged artificial prey presented to wild avian predators, we test whether distractive markings enhance concealment. In contrast to predictions, we find that markings, both circular and irregular shapes, increase predation compared with unmarked targets. Markings became increasingly costly as their contrast against the prey increased. Our experiments failed to find any empirical support for the hypothesis that distraction markings are an important aspect of camouflage in animals.