Dazzle camouflage, target tracking, and the confusion effect

Dazzling damselfish: investigating motion dazzle as a defence strategy in humbug damselfish (Dascyllus aruanus)

Many animals possess high-contrast body patterns. When moving, these patterns may create confusing or conflicting visual cues that affect a predator's ability to visually target or capture them, a phenomenon called motion dazzle. The dazzle patterns may generate different forms of optical illusion that can mislead observers about the shape, speed, trajectory and range of the animal. Moreover, it is possible that the disruptive visual effects of the high contrast body patterns can be enhanced when moving against a high contrast background. In this study, we used the humbug damselfish (Dascyllus aruanus) to model the apparent motion cues of its high contrast body stripes against high contrast background gratings of different widths and orientations, from the perspective of a predator. We found with higher frequency gratings, when the background is indiscriminable to a viewer, that the humbugs may rely on the confusing motion cues created by internal stripes. With lower frequency gratings, where the background is likely perceivable by a viewer, the humbugs can rely more on confusing motion cues induced by disruption of edges from both the background and body patterning. We also assessed whether humbugs altered their behaviour in response to different backgrounds. Humbugs remained closer and moved less overall in response to backgrounds with a spatial structure similar to their own striped body pattern, possibly to stay camouflaged against the background and thus avoid revealing themselves to potential predators. At backgrounds with higher frequency gratings, humbugs moved more which may represent a greater reliance on the internal contrast of the fish's striped body pattern to generate motion dazzle. It is possible that the humbug stripes provide multiple protective strategies depending on the context and that the fish may alter their behaviour depending on the background to maximise their protection.

A framework for understanding post-detection deception in predator-prey interactions

Predators and prey exist in persistent conflict that often hinges on deception-the transmission of misleading or manipulative signals-as a means for survival. Deceptive traits are widespread across taxa and sensory systems, representing an evolutionarily successful and common strategy. Moreover, the highly conserved nature of the major sensory systems often extends these traits past single species predator-prey interactions toward a broader set of perceivers. As such, deceptive traits can provide a unique window into the capabilities, constraints and commonalities across divergent and phylogenetically-related perceivers. Researchers have studied deceptive traits for centuries, but a unified framework for categorizing different types of post-detection deception in predator-prey conflict still holds potential to inform future research. We suggest that deceptive traits can be distinguished by their effect on object formation processes. Perceptual objects are composed of physical attributes (what) and spatial (where) information. Deceptive traits that operate after object formation can therefore influence the perception and processing of either or both of these axes. We build upon previous work using a perceiver perspective approach to delineate deceptive traits by whether they closely match the sensory information of another object or create a discrepancy between perception and reality by exploiting the sensory shortcuts and perceptual biases of their perceiver. We then further divide this second category, sensory illusions, into traits that distort object characteristics along either the what or where axes, and those that create the perception of whole novel objects, integrating the what/where axes. Using predator-prey examples, we detail each step in this framework and propose future avenues for research. We suggest that this framework will help organize the many forms of deceptive traits and help generate predictions about selective forces that have driven animal form and behavior across evolutionary time.

The origin of black and white coloration of the Asian tiger mosquito Aedes albopictus (Diptera: Culicidae)

Micro- and nanostructures of the white and black scales on the tarsi of the mosquito Aedes albopictus are analysed using scanning electron microscopy, transmission electron microscopy, and fluorescence microscopy. Reflectance spectra of the white areas are measured. No clear difference is present in the morphology of micro- and nanostructures of black and white scales in SEM and TEM, but black scales contain a dark pigment. The white colour of the scales has a structural origin. The structural white produced by the micro- and nanostructures of the scales on the tarsi of Ae. albopictus appears bright and is angle-dependent, since the reflected light changes according to the angle detection and according to the tarsus orientation. The optical appearance of the scale system of Ae. albopictus has a complex nature and can be explained by the combination of several effects. Among them, multiple refraction and reflection on the micro- and nanostructures of the scales are mainly responsible for the white appearance. The results suggest that mosquito scales, in addition to their superhydrophobic function, produce structural white. The biological role of white and black patches in mate recognition and defensive behaviour in the mosquitoes of the genus Aedes is hypothesized.

Water column use by reef fishes of different color patterns

ABSTRACT Color in animals responds to selective pressures and mediates the relationship between organism and environment. Reef fishes have the amplest variety of pigment cell types. This color patterns’ variety may function as camouflage and be related to spatial use. We tested the hypothesis that the coloration of reef fish relates to water column stratum occupation. We predicted that sedentary animals connected to the background take advantage of background matching or disruptive patterns; more mobile demersal species apply disruptive coloration or motion-dazzle; and that pelagic species tend to have silvery bodies. We classified color patterns and categorized the water column stratum use for the Brazilian reef fishes in FishBase. Our analyses confirmed that irregular contrasting contour breaks, suggestive of disruptive coloration, occurs in benthic species and that silvering color was more prevalent in the pelagic stratum. Our raw data suggested a higher frequency of contrasting regular stripes, typical of motion-dazzle, in demersal species. However, the considerable uncertainty around estimates did not confirm this pattern. Reef fishes coloration is correlated to occupation of different strata in the water column. This can be interpreted as fishes being adapted to these habitats and partially explaining the richness of color patterns among them.

Motion: enhancing signals and concealing cues

Animal colour patterns remain a lively focus of evolutionary and behavioural ecology, despite the considerable conceptual and technical developments over the last four decades. Nevertheless, our current understanding of the function and efficacy of animal colour patterns remains largely shaped by a focus on stationary animals, typically in a static background. Yet, this rarely reflects the natural world: most animals are mobile in their search for food and mates, and their surrounding environment is usually dynamic. Thus, visual signalling involves not only animal colour patterns, but also the patterns of animal motion and behaviour, often in the context of a potentially dynamic background. While motion can reveal information about the signaller by attracting attention or revealing signaller attributes, motion can also be a means of concealing cues, by reducing the likelihood of detection (motion camouflage, motion masquerade and flicker-fusion effect) or the likelihood of capture following detection (motion dazzle and confusion effect). The interaction between the colour patterns of the animal and its local environment is further affected by the behaviour of the individual. Our review details how motion is intricately linked to signalling and suggests some avenues for future research.

This Review has an associated Future Leader to Watch interview with the first author.

Summary: While motion can reveal information about the signaller, motion can also be a means of concealing cues by reducing the likelihood of detection or the likelihood of capture following detection.

Do bovids evolve hindquarter markings for anti-predation?

Conspicuous coloration in animals serves many functions such as anti-predation. Anti-predation strategies include motion dazzle and flash behavior. Motion dazzle markings can reduce the probability of being preyed on because the predators misjudge their movement. In flash behavior, prey demonstrate conspicuous cue while fleeing; the predators follow them; however, the prey hide their markings and the predators assume that the prey has vanished. To investigate whether bovids use conspicuous hindquarter markings as an anti-predatory behavior, we undertook phylogenetically controlled analyses to explore under what physiological characteristics and environmental factors bovids might have this color pattern. The results suggested that rump patches and tail markings were more prevalent in bovids living in larger-sized groups, which supports the hypothesis of intraspecific communication. Moreover, we observed the occurrence of conspicuous white hindquarter markings in bovids having smaller body size and living in larger groups, suggesting a motion dazzle function. However, the feature of facultative exposing color patterns (flash markings) was not associated with body size, which was inconsistent with predictions and implied that bovids may not adopt this as an anti-predator strategy. It was concluded that species in bovids with conspicuous white hindquarter markings adopt motion dazzle as an anti-predation strategy while fleeing and escaping from being prey on.

The evolution of patterning during movement in a large-scale citizen science game

The motion dazzle hypothesis posits that high contrast geometric patterns can cause difficulties in tracking a moving target and has been argued to explain the patterning of animals such as zebras. Research to date has only tested a small number of patterns, offering equivocal support for the hypothesis. Here, we take a genetic programming approach to allow patterns to evolve based on their fitness (time taken to capture) and thus find the optimal strategy for providing protection when moving. Our ‘Dazzle Bug’ citizen science game tested over 1.5 million targets in a touch screen game at a popular visitor attraction. Surprisingly, we found that targets lost pattern elements during evolution and became closely background matching. Modelling results suggested that targets with lower motion energy were harder to catch. Our results indicate that low contrast, featureless targets offer the greatest protection against capture when in motion, challenging the motion dazzle hypothesis.

In the corner of the eye: camouflaging motion in the peripheral visual field

Most animals need to move, and motion will generally break camouflage. In many instances, most of the visual field of a predator does not fall within a high-resolution area of the retina and so, when an undetected prey moves, that motion will often be in peripheral vision. We investigate how this can be exploited by prey, through different patterns of movement, to reduce the accuracy with which the predator can locate a cryptic prey item when it subsequently orients towards a target. The same logic applies for a prey species trying to localize a predatory threat. Using human participants as surrogate predators, tasked with localizing a target on peripherally viewed computer screens, we quantify the effects of movement (duration and speed) and target pattern. We show that, while motion is certainly detrimental to camouflage, should movement be necessary, some behaviours and surface patterns reduce that cost. Our data indicate that the phenotype that minimizes localization accuracy is unpatterned, having the mean luminance of the background, does not use a startle display prior to movement, and has short (below saccadic latency), fast movements.

Cows painted with zebra-like striping can avoid biting fly attack

Experimental and comparative studies suggest that the striped coats of zebras can prevent biting fly attacks. Biting flies are serious pests of livestock that cause economic losses in animal production. We hypothesized that cows painted with black and white stripes on their body could avoid biting fly attacks and show fewer fly-repelling behaviors. Six Japanese Black cows were assigned to treatments using a 3 × 3 Latin-square design. The treatments were black-and-white painted stripes, black painted stripes, and no stripes (all-black body surface). Recorded fly-repelling behaviors were head throw, ear beat, leg stamp, skin twitch, and tail flick. Photo images of the right side of each cow were taken using a commercial digital camera after every observation and biting flies on the body and each leg were counted from the photo images. Here we show that the numbers of biting flies on Japanese Black cows painted with black-and-white stripes were significantly lower than those on non-painted cows and cows painted only with black stripes. The frequencies of fly-repelling behaviors in cows painted with black-and-white stripes were also lower than those in the non-painted and black-striped cows. These results thus suggest that painting black-and-white stripes on livestock such as cattle can prevent biting fly attacks and provide an alternative method of defending livestock against biting flies without using pesticides in animal production, thereby proposing a solution for the problem of pesticide resistance in the environment.

What makes motion dazzle markings effective against predation?

Motion dazzle markings comprise patterns such as stripes and zig-zags that are postulated to protect moving prey by making predators misjudge the prey’s speed or trajectory. Recent experiments have provided conflicting results on their effect on speed perception and attack success. We focus on motion dazzle stripes and investigate the influence of four parameters—stripe orientation, stripe contrast, target size, and target speed—on perceived speed and attack success using a common experimental paradigm involving human “predators” attacking virtual moving targets on a computer touchscreen. We found that high-contrast stripes running parallel or perpendicular to the direction of motion reduce attack success compared to conspicuous uniform targets. Surprisingly, parallel stripes induced underestimation of speed, while perpendicular stripes induced overestimation of speed in relation to uniform black, suggesting that misjudgment of speed per se is sufficient to reduce attack accuracy. Across all the experiments, we found some support for parallel stripes inducing underestimation of target speed but these stripes reduced attack success only when targets were small, moved at an intermediate speed, and had high internal contrast. We suggest that prey features (e.g., size or speed) are an important determinant of capture success and that distortion of speed perception by a color pattern does not necessarily translate to reduced capture success of the prey. Overall, our results support the idea that striped patterns in prey animals can reduce capture in motion but are effective under a limited set of conditions.

Edge-Enhanced Disruptive Camouflage Impairs Shape Discrimination

Disruptive colouration (DC) is a form of camouflage comprised of areas of pigmentation across a target's surface that form false edges, which are said to impede detection by disguising the outline of the target. In nature, many species with DC also exhibit edge enhancement (EE); light areas have lighter edges and dark areas have darker edges. EE DC has been shown to undermine not only localisation but also identification of targets, even when they are not hidden (Sharman, Moncrieff, & Lovell, 2018). We use a novel task, where participants judge which "snake" is more "wiggly," to measure shape discrimination performance for three colourations (uniform, DC, and EE DC) and two backgrounds (leafy and uniform). We show that EE DC impairs shape discrimination even when targets are not hidden in a textured background. We suggest that this mechanism may contribute to misidentification of EE DC targets.

Benefits of zebra stripes: Behaviour of tabanid flies around zebras and horses

Averting attack by biting flies is increasingly regarded as the evolutionary driver of zebra stripes, although the precise mechanism by which stripes ameliorate attack by ectoparasites is unknown. We examined the behaviour of tabanids (horse flies) in the vicinity of captive plains zebras and uniformly coloured domestic horses living on a horse farm in Britain. Observations showed that fewer tabanids landed on zebras than on horses per unit time, although rates of tabanid circling around or briefly touching zebra and horse pelage did not differ. In an experiment in which horses sequentially wore cloth coats of different colours, those wearing a striped pattern suffered far lower rates of tabanid touching and landing on coats than the same horses wearing black or white, yet there were no differences in attack rates to their naked heads. In separate, detailed video analyses, tabanids approached zebras faster and failed to decelerate before contacting zebras, and proportionately more tabanids simply touched rather than landed on zebra pelage in comparison to horses. Taken together, these findings indicate that, up close, striped surfaces prevented flies from making a controlled landing but did not influence tabanid behaviour at a distance. To counteract flies, zebras swished their tails and ran away from fly nuisance whereas horses showed higher rates of skin twitching. As a consequence of zebras’ striping, very few tabanids successfully landed on zebras and, as a result of zebras’ changeable behaviour, few stayed a long time, or probed for blood.

The key role of behaviour in animal camouflage

Animal camouflage represents one of the most important ways of preventing (or facilitating) predation. It attracted the attention of the earliest evolutionary biologists, and today remains a focus of investigation in areas ranging from evolutionary ecology, animal decision-making, optimal strategies, visual psychology, computer science, to materials science. Most work focuses on the role of animal morphology per se, and its interactions with the background in affecting detection and recognition. However, the behaviour of organisms is likely to be crucial in affecting camouflage too, through background choice, body orientation and positioning; and strategies of camouflage that require movement. A wealth of potential mechanisms may affect such behaviours, from imprinting and self-assessment to genetics, and operate at several levels (species, morph, and individual). Over many years there have been numerous studies investigating the role of behaviour in camouflage, but to date, no effort to synthesise these studies and ideas into a coherent framework. Here, we review key work on behaviour and camouflage, highlight the mechanisms involved and implications of behaviour, discuss the importance of this in a changing world, and offer suggestions for addressing the many important gaps in our understanding of this subject.

Dynamic colour change and the confusion effect against predation

The confusion effect - the decreased attack-to-kill ratio of a predator with increase in prey group size - is thought to be one of the main reasons for the evolution of group living in animals. Despite much interest, the influence of prey coloration on the confusion effect is not well understood. We hypothesized that dynamic colour change in motion (due to interference coloration or flash marks), seen widely in many group living animals, enhances the confusion effect. Utilizing a virtual tracking task with humans, we found targets that dynamically changed colour during motion were more difficult to track than targets with background matching patterns, and this effect was stronger at larger group sizes. The current study thus provides the first empirical evidence for the idea that dynamic colour change can benefit animals in a group and may explain the widespread occurrence of dynamic colorations in group-living animals.

Ecological significance of dorsal polymorphism in a Batesian mimic snake

Batesian mimicry is the process in which harmless species adopt the appearance of a dangerous, aposematic species. In some prey species, both Batesian mimetic and non-Batesian morphs coexist, presupposing that both morphs have to be evolutionarily advantageous. The viperine snake, Natrix maura, exhibits a zigzag dorsal pattern and antipredatory behavior that mimics European vipers. This snake also has a striped dorsal pattern that coexists with the zigzag pattern. We have examined whether individuals belonging to different geographically structured clades were more likely to exhibit a certain dorsal pattern, and whether the zigzag pattern has a protective function by exposing artificial snakes to predation in natural environments, in addition to comparing antipredatory behavior between zigzag and striped snakes also in natural environments. Our results indicate that the striped pattern was not geographically structured, but habitat-dependent. Aerial predators less frequently attacked zigzag plasticine models than striped or unpatterned models. We detected a shift in antipredator behavior between the 2 morphs, as Batesian mimicking N. maura responded to an approaching potential predator by remaining immobile or fleeing at shorter distances than did striped ones. We conclude that Batesian mimics maintain the cryptic and aposematic value by resembling vipers, whereas in open habitats the non-Batesian mimic has altered its antipredator behavior to maintain its fitness.

Grab my tail: evolution of dazzle stripes and colourful tails in lizards

Understanding the functions of animal coloration has been a long-standing question in evolutionary biology. For example, the widespread occurrence of striking longitudinal stripes and colourful tails in lizards begs for an explanation. Experiments have suggested that colourful tails can deflect attacks towards the tail (the 'deflection' hypothesis), which is sacrificable in most lizards, thereby increasing the chance of escape. Studies also suggest that in moving lizards, longitudinal body stripes can redirect predators' strikes towards the tail through the 'motion dazzle' effect. Despite these experimental studies, the ecological factors associated with the evolution of such striking colorations remain unexplored. Here, we investigated whether predictions from motion dazzle and attack deflection could explain the widespread occurrence of these striking marks using comparative methods and information on eco-physiological variables (caudal autotomy, diel activity, microhabitat and body temperature) potentially linked to their functioning. We found both longitudinal stripes and colourful tails are associated with diurnal activity and with the ability to lose the tail. Compared to stripeless species, striped species are more likely to be ground-dwelling and have higher body temperature, emphasizing the connection of stripes to mobility and rapid escape strategy. Colourful tails and stripes have evolved multiple times in a correlated fashion, suggesting that their functions may be linked. Overall, our results together with previous experimental studies support the notion that stripes and colourful tails in lizards may have protective functions based on deflective and motion dazzle effects.

Anuran predators overcome visual illusion: dazzle coloration does not protect moving prey

Predators everywhere impose strong selection pressures on the morphology and behavior of their prey, but the resulting antipredator adaptations vary greatly among species. Studies of adaptive coloration in prey species have generally focused on cryptic or aposematic prey, with little consideration of color patterns in palatable mobile prey. Complex color patterns have been proposed to decrease the ability of visual predators to capture moving prey (motion dazzle effect). Most support for this hypothesis, however, comes from experiments with human subjects and simulated prey. We tested the motion dazzle effect using, for the first time, natural predators (cane toads, Rhinella marina) and live prey (house crickets, Acheta domesticus) with altered color patterns. We found no support for the motion dazzle effect as striped crickets did not fare better than solid colored ones. Crickets that spent more time moving, however, were more likely to be eaten. Our results suggest that motion specialized visual predators such as toads overcome the motion dazzle effect and impose stronger selection pressure on prey behavior than on coloration. These findings emphasize the importance of sensory specializations of predators in mediating antipredator strategies.

Camouflaging moving objects: crypsis and masquerade

Motion is generally assumed to “break” camouflage. However, although camouflage cannot conceal a group of moving animals, it may impair a predator’s ability to single one out for attack, even if that discrimination is not based on a color difference. Here, we use a computer-based task in which humans had to detect the odd one out among moving objects, with “oddity” based on shape. All objects were either patterned or plain, and either matched the background or not. We show that there are advantages of matching both group-mates and the background. However, when patterned objects are on a plain background (i.e., no background matching), the advantage of being among similarly patterned distractors is only realized when the group size is larger (10 compared to 5). In a second experiment, we present a paradigm for testing how coloration interferes with target-distractor discrimination, based on an adaptive staircase procedure for establishing the threshold. We show that when the predator only has a short time for decision-making, displaying a similar pattern to the distractors and the background affords protection even when the difference in shape between target and distractors is large. We conclude that, even though motion breaks camouflage, being camouflaged could help group-living animals reduce the risk of being singled out for attack by predators.

How camouflage works

For camouflage to succeed, an individual has to pass undetected, unrecognized or untargeted, and hence it is the processing of visual information that needs to be deceived. Camouflage is therefore an adaptation to the perception and cognitive mechanisms of another animal. Although this has been acknowledged for a long time, there has been no unitary account of the link between visual perception and camouflage. Viewing camouflage as a suite of adaptations to reduce the signal-to-noise ratio provides the necessary common framework. We review the main processes in visual perception and how animal camouflage exploits these. We connect the function of established camouflage mechanisms to the analysis of primitive features, edges, surfaces, characteristic features and objects (a standard hierarchy of processing in vision science). Compared to the commonly used research approach based on established camouflage mechanisms, we argue that our approach based on perceptual processes targeted by camouflage has several important benefits: specifically, it enables the formulation of more precise hypotheses and addresses questions that cannot even be identified when investigating camouflage only through the classic approach based on the patterns themselves. It also promotes a shift from the appearance to the mechanistic function of animal coloration.This article is part of the themed issue 'Animal coloration: production, perception, function and application'.

Marginal predation: do encounter or confusion effects explain the targeting of prey group edges?

Marginal predation, also known as the edge effect, occurs when aggregations of prey are preferentially targeted on their periphery by predators and has long been established in many taxa. Two main processes have been used to explain this phenomenon, the confusion effect and the encounter rate between predators and prey group edges. However, it is unknown at what size a prey group needs to be before marginal predation is detectable and to what extent each mechanism drives the effect. We conducted 2 experiments using groups of virtual prey being preyed upon by 3-spined sticklebacks (Gasterosteus aculeatus) to address these questions. In Experiment 1, we show that group sizes do not need to be large for marginal predation to occur, with this being detectable in groups of 16 or more. In Experiment 2, we find that encounter rate is a more likely explanation for marginal predation than the confusion effect in this system. We find that while confusion does affect predatory behaviors (whether or not predators make an attack), it does not affect marginal predation. Our results suggest that marginal predation is a more common phenomenon than originally thought as it also applies to relatively small groups. Similarly, as marginal predation does not need the confusion effect to occur, it may occur in a wider range of predator–prey species pairings, for example those where the predators search for prey using nonvisual sensory modalities.

Diverted by dazzle: perceived movement direction is biased by target pattern orientation

'Motion dazzle' is the hypothesis that predators may misjudge the speed or direction of moving prey which have high-contrast patterning, such as stripes. However, there is currently little experimental evidence that such patterns cause visual illusions. Here, observers binocularly tracked a Gabor target, moving with a linear trajectory randomly chosen within 18° of the horizontal. This target then became occluded, and observers were asked to judge where they thought it would later cross a vertical line to the side. We found that internal motion of the stripes within the Gabor biased judgements as expected: Gabors with upwards internal stripe motion relative to the overall direction of motion were perceived to be crossing above Gabors with downwards internal stripe movement. However, surprisingly, we found a much stronger effect of the rigid pattern orientation. Patches with oblique stripes pointing upwards relative to the direction of motion were perceived to cross above patches with downward-pointing stripes. This effect occurred only at high speeds, suggesting that it may reflect an orientation-dependent effect in which spatial signals are used in direction judgements. These findings have implications for our understanding of motion dazzle mechanisms and how human motion and form processing interact.

Dazzle camouflage and the confusion effect: the influence of varying speed on target tracking

The formation of groups is a common strategy to avoid predation in animals, and recent research has indicated that there may be interactions between some forms of defensive coloration, notably high-contrast ‘dazzle camouflage’, and one of the proposed benefits of grouping: the confusion effect. However, research into the benefits of dazzle camouflage has largely used targets moving with constant speed. This simplification may not generalize well to real animal systems, where a number of factors influence both within- and between-individual variation in speed. Departure from the speed of your neighbours in a group may be predicted to undermine the confusion effect. This is because individual speed may become a parameter through which the observer can individuate otherwise similar targets: an ‘oddity effect’. However, dazzle camouflage patterns are thought to interfere with predator perception of speed and trajectory. The current experiment investigated the possibility that such patterns could ameliorate the oddity effect caused by within-group differences in prey speed. We found that variation in speed increased the ease with which participants could track targets in all conditions. However, we found no evidence that motion dazzle camouflage patterns reduced oddity effects based on this variation in speed, a result that may be informative about the mechanisms behind this form of defensive coloration. In addition, results from those conditions most similar to those of published studies replicated previous results, indicating that targets with stripes parallel to the direction of motion are harder to track, and that this pattern interacts with the confusion effect to a greater degree than background matching or orthogonal-to-motion striped patterns.

•

Variation in speed in groups induces the oddity effect, reducing predator confusion.

•

Dazzle camouflage does not ameliorate this oddity effect.

•

Parallel striped targets in groups are harder to track than other targets.

The confusion effect when attacking simulated three-dimensional starling flocks

The confusion effect describes the phenomenon of decreasing predator attack success with increasing prey group size. However, there is a paucity of research into the influence of this effect in coherent groups, such as flocks of European starlings (Sturnus vulgaris). Here, for the first time, we use a computer game style experiment to investigate the confusion effect in three dimensions. To date, computerized studies on the confusion effect have used two-dimensional simulations with simplistic prey movement and dynamics. Our experiment is the first investigation of the effects of flock size and density on the ability of a (human) predator to track and capture a target starling in a realistically simulated three-dimensional flock of starlings. In line with the predictions of the confusion effect, modelled starlings appear to be safer from predation in larger and denser flocks. This finding lends credence to previous suggestions that starling flocks have anti-predator benefits and, more generally, it suggests that active increases in density in animal groups in response to predation may increase the effectiveness of the confusion effect.

Contrast, contours and the confusion effect in dazzle camouflage

'Motion dazzle camouflage' is the name for the putative effects of highly conspicuous, often repetitive or complex, patterns on parameters important in prey capture, such as the perception of speed, direction and identity. Research into motion dazzle camouflage is increasing our understanding of the interactions between visual tracking, the confusion effect and defensive coloration. However, there is a paucity of research into the effects of contrast on motion dazzle camouflage: is maximal contrast a prerequisite for effectiveness? If not, this has important implications for our recognition of the phenotype and understanding of the function and mechanisms of potential motion dazzle camouflage patterns. Here we tested human participants' ability to track one moving target among many identical distractors with surface patterns designed to test the influence of these factors. In line with previous evidence, we found that targets with stripes parallel to the object direction of motion were hardest to track. However, reduction in contrast did not significantly influence this result. This finding may bring into question the utility of current definitions of motion dazzle camouflage, and means that some animal patterns, such as aposematic or mimetic stripes, may have previously unrecognized multiple functions.