Concealed by conspicuousness: distractive prey markings and backgrounds

High-contrast markings, called distractive or dazzle markings, have been suggested to draw and hold the attention of a viewer, thus hindering detection or recognition of revealing prey characteristics, such as the body outline. We tested this hypothesis in a predation experiment with blue tits (Cyanistes caeruleus) and artificial prey. We also tested whether this idea can be extrapolated to the background appearance and whether high-contrast markings in the background would improve prey concealment. We compared search times for a high-contrast range prey (HC-P) and a low-contrast range prey (LC-P) in a high-contrast range background (HC-B) and a low-contrast range background (LC-B). The HC-P was more difficult to detect in both backgrounds, although it did not match the LC-B. Also, both prey types were more difficult to find in the HC-B than in the LC-B, in spite of the mismatch of the LC-P. In addition, the HC-P was more difficult to detect, in both backgrounds, when compared with a generalist prey, not mismatching either background. Thus, we conclude that distractive prey pattern markings and selection of microhabitats with distractive features may provide an effective way to improve camouflage. Importantly, high-contrast markings, both as part of the prey coloration and in the background, can indeed increase prey concealment.     

Behaviourally mediated crypsis in two nocturnal moths with contrasting appearance

The natural resting orientations of several species of nocturnal moth on tree trunks were recorded over a three-month period in eastern Ontario, Canada. Moths from certain genera exhibited resting orientation distributions that differed significantly from random, whereas others did not. In particular, Catocala spp. collectively tended to orient vertically, whereas subfamily Larentiinae representatives showed a variety of orientations that did not differ significantly from random. To understand why different moth species adopted different orientations, we presented human subjects with a computer-based detection task of finding and ‘attacking’ Catocala cerogama and Euphyia intermediata target images at different orientations when superimposed on images of sugar maple (Acer saccharum) trees. For both C. cerogama and E. intermediata, orientation had a significant effect on survivorship, although the effect was more pronounced in C. cerogama. When the tree background images were flipped horizontally the optimal orientation changed accordingly, indicating that the detection rates were dependent on the interaction between certain directional appearance features of the moth and its background. Collectively, our results suggest that the contrasting wing patterns of the moths are involved in background matching, and that the moths are able to improve their crypsis through appropriate behavioural orientation.     

Empirical tests of the role of disruptive coloration in reducing detectability

Disruptive patterning is a potentially universal camouflage technique that is thought to enhance concealment by rendering the detection of body shapes more difficult. In a recent series of field experiments, artificial moths with markings that extended to the edges of their 'wings' survived at higher rates than moths with the same edge patterns inwardly displaced. While this result seemingly indicates a benefit to obscuring edges, it is possible that the higher density markings of the inwardly displaced patterns concomitantly reduced their extent of background matching. Likewise, it has been suggested that the mealworm baits placed on the artificial moths could have created differential contrasts with different moth patterns. To address these concerns, we conducted controlled trials in which human subjects searched for computer-generated moth images presented against images of oak trees. Moths with edge-extended disruptive markings survived at higher rates, and took longer to find, than all other moth types, whether presented sequentially or simultaneously. However, moths with no edge markings and reduced interior pattern density survived better than their high-density counterparts, indicating that background matching may have played a so-far unrecognized role in the earlier experiments. Our disruptively patterned non-background-matching moths also had the lowest overall survivorship, indicating that disruptive coloration alone may not provide significant protection from predators. Collectively, our results provide independent support for the survival value of disruptive markings and demonstrate that there are common features in human and avian perception of camouflage.     

Great tits (Parus major) searching for artificial prey: implications for cryptic coloration and symmetry

It has been suggested that bilateral symmetry may impose a costfor animals relying on camouflage because symmetric color patternsmight increase the risk of detection. We tested the effect ofsymmetry on crypsis, carrying out a predation experiment withgreat tits (Parus major) and black-and-white–patterned,artificial prey items and background. First, we found that detectiontime was significantly longer for a highly cryptic, asymmetricpattern based on a random sample of the background than forits symmetric variants. Second, we were able to arrange theelements of a prey pattern in a way that the resulting asymmetricpattern was highly cryptic and, furthermore, its symmetric variantwas highly cryptic as well. We conclude that symmetry may imposea substantial cost on cryptic patterns, but this cost variesamong patterns. This suggests that for prey, which predatorstypically view from an angle exposing their symmetry, selectionfor pattern asymmetry may be less important and selection fordecreased detectability cost of symmetry may be more importantthan previously thought. This may help to understand the existenceof so many prey with cryptic, symmetric color patterns.     

Coincident disruptive coloration

Even if an animal matches its surroundings perfectly in colour and texture, any mismatch between the spatial phase of its pattern and that of the background, or shadow created by its three-dimensional relief, is potentially revealing. Nevertheless, for camouflage to be fully broken, the shape must be recognizable. Disruptive coloration acts against object recognition by the use of high-contrast internal colour boundaries to break up shape and form. As well as the general outline, characteristic features such as eyes and limbs must also be concealed; this can be achieved by having the colour patterns on different, but adjacent, body parts aligned to match each other (i.e. in phase). Such 'coincident disruptive coloration' ensures that there is no phase disjunction where body parts meet, and causes different sections of the body to blend perceptually. We tested this theory using field experiments with predation by wild birds on artificial moth-like targets, whose wings and (edible pastry) bodies had colour patterns that were variously coincident or not. We also carried out an experiment with humans searching for analogous targets on a computer screen. Both experiments show that coincident disruptive coloration is an effective mechanism for concealing an otherwise revealing body form.     

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.     

Disruptive camouflage impairs object recognition

Whether hiding from predators, or avoiding battlefield casualties, camouflage is widely employed to prevent detection. Disruptive coloration is a seemingly well-known camouflage mechanism proposed to function by breaking up an object''s salient features (for example their characteristic outline), rendering objects more difficult to recognize. However, while a wide range of animals are thought to evade detection using disruptive patterns, there is no direct experimental evidence that disruptive coloration impairs recognition. Using humans searching for computer-generated moth targets, we demonstrate that the number of edge-intersecting patches on a target reduces the likelihood of it being detected, even at the expense of reduced background matching. Crucially, eye-tracking data show that targets with more edge-intersecting patches were looked at for longer periods prior to attack, and passed-over more frequently during search tasks. We therefore show directly that edge patches enhance survivorship by impairing recognition, confirming that disruptive coloration is a distinct camouflage strategy, not simply an artefact of background matching.     

Background choice as an anti-predator strategy: the roles of background matching and visual complexity in the habitat choice of the least killifish

Because background matching improves concealment, prey animals have traditionally been expected to prefer parts of the habitat that match their visual appearance. However, empirical support for this is scarce. Moreover, this idea has recently been challenged by an alternative hypothesis: visual complexity of the background impedes prey detection, and hence prey could instead prefer complex parts of the habitat. We used the least killifish to test, with and without predation threat, for the importance of the visual similarity between the fish and the background, and the level of visual complexity of the background. We observed their choice between backgrounds patterned with elements based on the longitudinal black stripe of the fish. Predation risk was important under some circumstances, and induced a preference for a background of matching horizontal stripes compared with mismatching vertical stripes. Interestingly, females under predation threat showed a preference for a complex background of randomly oriented and overlapping stripes compared with matching stripes, whereas males did not discriminate between these two. Additionally, males showed a preference for matching stripes compared with complex shapes, whereas females did not discriminate between these backgrounds. We conclude that matching is important in the choice for safe habitat, but some aspects of visual complexity may override or act together with background matching.     

动物的伪装方式

: 伪装是动物防御性体色最重要的功能之一,能减少被捕食者检测和识别的风险。本文综述了隐蔽、乔装、运动炫和运动伪装等4种伪装方式的研究进展,并指出当前研究中存在的一些问题,以期为动物伪装进化的研究提供参考。     

Spots and stripes: ecology and colour pattern evolution in butterflyfishes

The incredible diversity of colour patterns in coral reef fishes has intrigued biologists for centuries. Yet, despite the many proposed explanations for this diversity in coloration, definitive tests of the role of ecological factors in shaping the evolution of particular colour pattern traits are absent. Patterns such as spots and eyespots (spots surrounded by concentric rings of contrasting colour) have often been assumed to function for predator defence by mimicking predators'' enemies'' eyes, deflecting attacks or intimidating predators, but the evolutionary processes underlying these functions have never been addressed. Striped body patterns have been suggested to serve for both social communication and predator defence, but the impact of ecological constraints remains unclear. We conducted the first comparative analysis of colour pattern diversity in butterflyfishes (Family: Chaetodontidae), fishes with conspicuous spots, eyespots and wide variation in coloration. Using a dated molecular phylogeny of 95 species (approx. 75% of the family), we tested whether spots and eyespots have evolved characteristics that are consistent with their proposed defensive function and whether the presence of spots and body stripes is linked with species'' body length, dietary complexity, habitat diversity or social behaviour. Contrary to our expectations, spots and eyespots appeared relatively recently in butterflyfish evolution and are highly evolutionarily labile, suggesting that they are unlikely to have played an important part in the evolutionary history of the group. Striped body patterns showed correlated evolution with a number of ecological factors including habitat type, sociality and dietary complexity. Our findings question the prevailing view that eyespots are an evolutionary response to predation pressure, providing a valuable counter example to the role of these markings as revealed in other taxa.     

The effects of pattern symmetry on detection of disruptive and background-matching coloration

Two, logically distinct but sometimes compatible, mechanismsof camouflage are background-matching and disruptive coloration.In the former, an animal's coloration comprises a random sampleof the background, and so target–background discriminationis impeded. In the latter, object or feature recognition iscompromised by placing bold, high-contrast colors so that theybreak up the prey's body into apparently unconnected objects.Recent experimental evidence for the utility of disruptive colors,above and beyond that conferred by background matching, hasbeen based on artificial prey with patterns lacking a planeof symmetry. However, it is plausible that the bilateral symmetrypresent in natural prey may compromise the efficiency of disruptivecoloration, on account of the potency of symmetry as a cue invisual search. In this study, we tested this prediction in thefield, by tracking the "survival" under bird predation of artificialmothlike targets placed on oak trees. These had background-matchingcolor patches placed either disruptively or nondisruptivelyand with or without bilateral symmetry. We found that symmetryreduced the effectiveness of both nondisruptive and disruptivebackground-matching coloration to a similar degree so that thenegative effects of symmetry on concealment are no greater fordisruptive than nondisruptive patterns.     

Revisiting Abbott Thayer: non-scientific reflections about camouflage in art,war and zoology

This paper reviews the achievements of Abbott Handerson Thayer (1849–1921), an American painter and naturalist whose pioneering writings on animal camouflage addressed shared concerns among artists, zoologists and military tacticians. It discusses his beliefs about camouflage (both natural and military) in the context of his training as an artist, with particular emphasis on three of his major ideas: countershading, ruptive (or disruptive) coloration and background picturing.     

Can't tell the caterpillars from the trees: countershading enhances survival in a woodland

Perception of the body's outline and three-dimensional shape arises from visual cues such as shading, contour, perspective and texture. When a uniformly coloured prey animal is illuminated from above by sunlight, a shadow may be cast on the body, generating a brightness contrast between the dorsal and ventral surfaces. For animals such as caterpillars, which live among flat leaves, a difference in reflectance over the body surface may degrade the degree of background matching and provide cues to shape from shading. This may make otherwise cryptic prey more conspicuous to visually hunting predators. Cryptically coloured prey are expected to match their substrate in colour, pattern and texture (though disruptive patterning is an exception), but they may also abolish self-shadowing and therefore either reduce shape cues or maintain their degree of background matching through countershading: a gradation of pigment on the body of an animal so that the surface closest to illumination is darker. In this study, we report the results from a series of field experiments where artificial prey resembling lepidopteran larvae were presented on the upper surfaces of beech tree branches so that they could be viewed by free-living birds. We demonstrate that countershading is superior to uniform coloration in terms of reducing attack by free-living predators. This result persisted even when we fixed prey to the underside of branches, simulating the resting position of many tree-living caterpillars. Our experiments provide the first demonstration, in an ecologically valid visual context, that shadowing on bodies (such as lepidopteran larvae) provides cues that visually hunting predators use to detect potential prey species, and that countershading counterbalances shadowing to enhance cryptic protection.     

Animal camouflage: compromise or specialize in a 2 patch-type environment?

Many animals possess camouflage markings that reduce the riskof detection by visually hunting predators. A key aspect ofcamouflage involves mimicking the background against which theanimal is viewed. However, most animals experience a wide varietyof backgrounds and cannot change their external appearance tomatch each selectively. We investigate whether such animalsshould adopt camouflage specialized with respect to one backgroundor adopt a compromise between the attributes of multiple backgrounds.We do this using a model consisting of predators that hunt preyin patches of 2 different types, where prey adopt the camouflagethat minimizes individual risk of predation. We show that theoptimal strategy of the prey is affected by a number of factors,including the relative frequencies of the patch types, the traveltime of predators between patches, the mean prey number in eachpatch type, and the trade-off function between the levels ofcrypsis in the patch types. We find evidence that both specialistand compromise strategies of prey camouflage are favored underdifferent model parameters, indicating that optimal concealmentmay not be as straightforward as previously thought.