Motion dazzle and camouflage as distinct anti-predator defenses

Abstract

BackgroundCamouflage patterns that hinder detection and/or recognition by antagonists are widely studied in both human and animal contexts. Patterns of contrasting stripes that purportedly degrade an observer's ability to judge the speed and direction of moving prey ('motion dazzle') are, however, rarely investigated. This is despite motion dazzle having been fundamental to the appearance of warships in both world wars and often postulated as the selective agent leading to repeated patterns on many animals (such as zebra and many fish, snake, and invertebrate species). Such patterns often appear conspicuous, suggesting that protection while moving by motion dazzle might impair camouflage when stationary. However, the relationship between motion dazzle and camouflage is unclear because disruptive camouflage relies on high-contrast markings. In this study, we used a computer game with human subjects detecting and capturing either moving or stationary targets with different patterns, in order to provide the first empirical exploration of the interaction of these two protective coloration mechanisms.ResultsMoving targets with stripes were caught significantly less often and missed more often than targets with camouflage patterns. However, when stationary, targets with camouflage markings were captured less often and caused more false detections than those with striped patterns, which were readily detected.ConclusionsOur study provides the clearest evidence to date that some patterns inhibit the capture of moving targets, but that camouflage and motion dazzle are not complementary strategies. Therefore, the specific coloration that evolves in animals will depend on how the life history and ontogeny of each species influence the trade-off between the costs and benefits of motion dazzle and camouflage.

Paradox lost: variable colour-pattern geometry is associated with differences in movement in aposematic frogs

“…Within a single population, frogs with more elongated patterns move continuously in a given direction rather than randomly. This pattern-movement combination might create the illusion of a static pattern or a pattern with a greatly reduced speed that affects predators' abilities to track the trajectory of moving individuals and predict their attack angle [11,14]. This may be more pronounced when movements occur at a higher speed [22,23] and over longer segments [15], as in these frogs.…”

Camouflage, detection and identification of moving targets

“…Together, these effects mean that an individual target moving on its own is highly conspicuous [16]. Under stationary conditions camouflage patterns (BM and disruptive) have been found to be successful at preventing the capture of a target.…”

The function of zebra stripes

“…Predation has been the predominant factor included in a number of hypotheses for body striping in equids centering on avoiding predation through confusing predators, tricking them into misjudging the size of their prey or the speed of the prey, thereby miscalculating the final leap, by making it difficult to single out a member of the herd or through aspects of striping being a signal of individual quality tied to flight speed 10,19,21,50,51 . All indicate that stripes should have evolved in the presence of large predators, yet there was no strong congruence between striping on any part of the animal at the species or subspecies level and close sympatry with lions, except for leg stripe intensity at the species level, driven particularly by the extinct Barbary lion and extinct Altas African wild ass co-occurring in the Maghreb.…”

“…Functional hypotheses fall into five broad categories: a form of crypsis probably matching a woodland background, disrupting predatory attack, reducing thermal load, having a social function and avoiding ectoparasite attack [5][6][7] . Only two have received more than passing attention: humans find moving striped objects difficult to target accurately on a computer screen, suggesting a possible motion dazzle confusion effect [8][9][10] , and tsetse flies, stomoxys stable flies and tabanid biting flies are less likely to land on black and white striped than on uniform surfaces [11][12][13][14] .…”