Camouflage, detection and identification of moving targets

Abstract

Nearly all research on camouflage has investigated its effectiveness for concealing stationary objects. However, animals have to move, and patterns that only work when the subject is static will heavily constrain behaviour. We investigated the effects of different camouflages on the three stages of predation-detection, identification and capture-in a computer-based task with humans. An initial experiment tested seven camouflage strategies on static stimuli. In line with previous literature, background-matching and disruptive patterns were found to be most successful. Experiment 2 showed that if stimuli move, an isolated moving object on a stationary background cannot avoid detection or capture regardless of the type of camouflage. Experiment 3 used an identification task and showed that while camouflage is unable to slow detection or capture, camouflaged targets are harder to identify than uncamouflaged targets when similar background objects are present. The specific details of the camouflage patterns have little impact on this effect. If one has to move, camouflage cannot impede detection; but if one is surrounded by similar targets (e.g. other animals in a herd, or moving background distractors), then camouflage can slow identification. Despite previous assumptions, motion does not entirely 'break' camouflage.

Camouflage and Perceptual Organization in the Animal Kingdom

“…Correlated motion is a strong cue to grouping, so that an otherwise highly camouflaged object is readily segregated from the background because its pattern elements share a common fate absent in otherwise identical background elements. Experiments on the detection of targets on complex backgrounds indicate that, for single targets, neither background matching nor disruptive camouflage offer any benefits (Hall et al 2013). This would explain why big cats stalking prey, and soldiers moving across open ground, move in a combination of stealthy motion interspersed with frequent pauses.…”

Escape Distance in Ground-Nesting Birds Differs with Individual Level of Camouflage

“…For cryptic animals, the degree of individual background matching should influence the decision of when to sit tight or to flee from an approaching predator. Movement has been shown to break the effects of camouflage (Stevens et al 2011;Hall et al 2013), presenting a cost to fleeing by revealing the animal's presence and location, and suggesting that camouflage and escape behaviour are likely to be linked. In situations where animals are caring for vulnerable offspring, the movement of a fleeing parent may betray the location of eggs or immobile young, such that escape decisions might also be influenced by the camouflage of offspring.…”

Disruptive colouration in reef fish: does matching the background reduce predation risk?

“…whether background matching or disruptive) are not influential in decreasing predation likelihood, as long as the pattern is at least similar to the background. It is the presence of other similarly patterned objects that increase protection (Hall et al, 2013;Stevens et al, 2011). The humbug has a body pattern similar to that of a zebra and congregates in small groups, suggesting an increased confusion effect due to the presence of similarly patterned objects (both humbug and branching coral background).…”

“…Background matching is most effective when animals are relatively stationary, as movement will often break camouflage and cause an animal to become more detectable to predatory visual systems (Hall et al, 2013;Ioannou and Krause, 2009;Julesz, 1971). Countershading is used to describe the difference in brightness between the ventral (lighter) and dorsal (darker) sides of a fish.…”