Disruptive eye mask

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Gaboon viper, its eye concealed by a disruptive mask Bitis gabonica rhinoceros.JPG
Gaboon viper, its eye concealed by a disruptive mask

Disruptive eye masks are camouflage markings that conceal the eyes of an animal from its predators or prey. They are used by prey, to avoid being seen by predators, and by predators to help them approach their prey.

Contents

The eye has a distinctive shape and dark coloration dictated by its function, and it is housed in the vulnerable head, making it a natural target for predators. It can be camouflaged by a suitable disruptive pattern arranged to run up to or through the eye, sometimes forming a camouflage eyestripe. The illusion is completed in some animals by a false eye or false head somewhere else on the body, in a form of automimicry.

Disruptive eye masks are seen on a variety of animals, both invertebrates such as grasshoppers and vertebrates, including fish, frogs, birds and snakes. Eye masks were first noticed by the American artist Abbott Handerson Thayer in 1909, and analysed extensively by the zoologist Hugh Cott in 1940. However, in 2005 the evolutionary zoologist Tim Caro could still observe that the assumption that eye masks served as camouflage had not been tested systematically.

History

Early investigators Abbott Handerson Thayer and Hugh Cott noted that active juvenile birds like this little ringed plover chick have boldly disruptive patterns that camouflage the eye. Little ringed plover - chick.jpg
Early investigators Abbott Handerson Thayer and Hugh Cott noted that active juvenile birds like this little ringed plover chick have boldly disruptive patterns that camouflage the eye.
Cott used this diagram to illustrate "the inherent conspicuousness of an eye-spot", and hence to justify the need for a disruptive eye mask. Cott's diagram illustrating the inherent conspicuousness of an eye-spot.jpg
Cott used this diagram to illustrate "the inherent conspicuousness of an eye-spot", and hence to justify the need for a disruptive eye mask.

The American artist Abbott Handerson Thayer mentioned the "masking" of the eyes of birds and mammals in his 1909 book Concealing-Coloration in the Animal Kingdom , stating that this was found mainly in birds, such as plovers, and predatory mammals. He noted that "it is very effective .. as it completely breaks the eye's otherwise conspicuous circular or oval outline. [2]

The zoologist Hugh Cott identified the value of concealing the eye in his 1940 book Adaptive Coloration in Animals . He notes the "inherent conspicuousness of an eye-spot", which "stands out from everything else, and rivets the attention", making the point with a diagram containing one small eyespot and many larger features: the eyespot immediately attracts the viewer's attention. [1] The image has been used elsewhere, for example in Tim Newark's 2007 book on camouflage, where Newark noted that Cott's image proved the point, as "the eye of a vertebrate, with its dense black pupil, stands out from the most jumbled backgrounds, as Cott's illustration demonstrates." [3] Cott argued that "no scheme of camouflage will be completely effective which does not mask or modify the appearance of the eye". [1] He mentioned, as "beautiful examples" of face patterns that achieve this, the swamp viper and the Gaboon viper. [4] In his words:

The disruptive value of a pattern lies in its tendency to hide the real form of an animal by suggesting a false form to the eye. So long as the false configuration is recognized in preference to the real one, concealment will be effected. [5]

Cott described disruptive eye masks as a special case of a coincident disruptive pattern, one that provides camouflage by joining together parts of the body to create a new appearance which contradicts the actual structures present. [6] On camouflage eyestripes, he noted that "more or less well-defined ocular bands or stripes" are found in many species of bird, including the nuthatch, snipe, whimbrel, ringed plover, and turnstone, and thought it significant that these patterns were associated with active young that leave the nest early, as in the ringed plover. He recorded that "what appear to be markings of similar significance" are found in mammals such as gemsbok, sable antelope, Grant's gazelle and vizcacha. [7]

In 1989, J. L. Cloudsley-Thompson noted that camouflage eyestripes are also found in many reptiles including slender arboreal vine snakes, numerous tropical fish such as the angelfish and garfish, and a wide variety of amphibians including the common frog. [8]

The evolutionary zoologist Tim Caro observed in 2005 that "the whole topic of disruptive coloration needs systematic analysis". [9] Caro noted that in mammals, "no systematic tests of this idea are available", but that dark patches around the eyes, which would tend to draw attention to the eye instead of camouflaging it, are associated with grassland and terrestrial carnivores as well as riparian animals, suggesting the function of reducing glare, or perhaps of aposematism. [9]

Pattern

G. W. Barlow, noting Cott's examples, analysed fish "eye-lines" in 1972, finding a relationship between angle of line and both body shape and angle of forehead. He found that fast-swimming species had longitudinal lines and long bodies; deep-bodied fish had vertical bars and the ability to turn abruptly. Many barred patterns were in his opinion "obviously an adaptation for crypsis" (camouflage). He concluded that stripes and bars were both social signals and antipredator adaptations. [10]

In 1981, Leah and Benjamin Gavish tested patterns that conceal birds' eyes using patterns and human observers. They found that patterns which allow the eye to protrude from the dark area concealed the eye best, calling this the "borderline eye effect". [11]

Some animals such as butterflyfish combine the camouflaging of the eye with an eyespot somewhere else on the body, possibly giving the impression that the animal's head is located there. [12] In 2013, Karin Kjernsmo and Sami Merilaita showed using artificial prey and predatory fish (three-spined sticklebacks) that such eyespots diverted predators' attacks from the vulnerable head. [13]

Related Research Articles

<span class="mw-page-title-main">Camouflage</span> Concealment in plain sight by any means, e.g. colour, pattern and shape

Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the battledress of a modern soldier, and the leaf-mimic katydid's wings. A third approach, motion dazzle, confuses the observer with a conspicuous pattern, making the object visible but momentarily harder to locate, as well as making general aiming easier. The majority of camouflage methods aim for crypsis, often through a general resemblance to the background, high contrast disruptive coloration, eliminating shadow, and countershading. In the open ocean, where there is no background, the principal methods of camouflage are transparency, silvering, and countershading, while the ability to produce light is among other things used for counter-illumination on the undersides of cephalopods such as squid. Some animals, such as chameleons and octopuses, are capable of actively changing their skin pattern and colours, whether for camouflage or for signalling. It is possible that some plants use camouflage to evade being eaten by herbivores.

<span class="mw-page-title-main">Anti-predator adaptation</span> Defensive feature of prey for selective advantage

Anti-predator adaptations are mechanisms developed through evolution that assist prey organisms in their constant struggle against predators. Throughout the animal kingdom, adaptations have evolved for every stage of this struggle, namely by avoiding detection, warding off attack, fighting back, or escaping when caught.

<span class="mw-page-title-main">Abbott Handerson Thayer</span> American painter (1849–1921)

Abbott Handerson Thayer was an American artist, naturalist, and teacher. As a painter of portraits, figures, animals, and landscapes, he enjoyed a certain prominence during his lifetime, and his paintings are represented in major American art collections. He is perhaps best known for his 'angel' paintings, some of which use his children as models.

<span class="mw-page-title-main">Crypsis</span> Aspect of animal behaviour and morphology

In ecology, crypsis is the ability of an animal or a plant to avoid observation or detection by other animals. It may be a predation strategy or an antipredator adaptation. Methods include camouflage, nocturnality, subterranean lifestyle and mimicry. Crypsis can involve visual, olfactory or auditory concealment. When it is visual, the term cryptic coloration, effectively a synonym for animal camouflage, is sometimes used, but many different methods of camouflage are employed by animals or plants.

<span class="mw-page-title-main">Hugh B. Cott</span> English zoologist and camouflage expert (1900–1987)

Hugh Bamford Cott was a British zoologist, an authority on both natural and military camouflage, and a scientific illustrator and photographer. Many of his field studies took place in Africa, where he was especially interested in the Nile crocodile, the evolution of pattern and colour in animals. During the Second World War, Cott worked as a camouflage expert for the British Army and helped to influence War Office policy on camouflage. His book Adaptive Coloration in Animals (1940), popular among serving soldiers, was the major textbook on camouflage in zoology of the twentieth century. After the war, he became a Fellow of Selwyn College, Cambridge. As a Fellow of the Zoological Society of London, he undertook expeditions to Africa and the Amazon to collect specimens, mainly reptiles and amphibians.

<span class="mw-page-title-main">Countershading</span> Camouflage to counteract self-shading

Countershading, or Thayer's law, is a method of camouflage in which an animal's coloration is darker on the top or upper side and lighter on the underside of the body. This pattern is found in many species of mammals, reptiles, birds, fish, and insects, both in predators and in prey.

<span class="mw-page-title-main">Eyespot (mimicry)</span> Eye-like marking used for mimicry or distraction

An eyespot is an eye-like marking. They are found in butterflies, reptiles, cats, birds and fish.

<span class="mw-page-title-main">Animal coloration</span> General appearance of an animal

Animal colouration is the general appearance of an animal resulting from the reflection or emission of light from its surfaces. Some animals are brightly coloured, while others are hard to see. In some species, such as the peafowl, the male has strong patterns, conspicuous colours and is iridescent, while the female is far less visible.

<span class="mw-page-title-main">Underwater camouflage</span> Camouflage in water, mainly by transparency, reflection, counter-illumination

Underwater camouflage is the set of methods of achieving crypsis—avoidance of observation—that allows otherwise visible aquatic organisms to remain unnoticed by other organisms such as predators or prey.

<span class="mw-page-title-main">Disruptive coloration</span> Camouflage to break up an objects outlines

Disruptive coloration is a form of camouflage that works by breaking up the outlines of an animal, soldier or military vehicle with a strongly contrasting pattern. It is often combined with other methods of crypsis including background colour matching and countershading; special cases are coincident disruptive coloration and the disruptive eye mask seen in some fishes, amphibians, and reptiles. It appears paradoxical as a way of not being seen, since disruption of outlines depends on high contrast, so the patches of colour are themselves conspicuous.

<i>Adaptive Coloration in Animals</i> 1940 textbook on camouflage, mimicry and aposematism by Hugh Cott

Adaptive Coloration in Animals is a 500-page textbook about camouflage, warning coloration and mimicry by the Cambridge zoologist Hugh Cott, first published during the Second World War in 1940; the book sold widely and made him famous.

<i>Concealing-Coloration in the Animal Kingdom</i> Book by Abbott Handerson Thayer

Concealing-Coloration in the Animal Kingdom: An Exposition of the Laws of Disguise Through Color and Pattern; Being a Summary of Abbott H. Thayer’s Discoveries is a book published ostensibly by Gerald H. Thayer in 1909, and revised in 1918, but in fact a collaboration with and completion of his father Abbott Handerson Thayer's major work.

<span class="mw-page-title-main">Deimatic behaviour</span> Bluffing display of an animal used to startle or scare a predator

Deimatic behaviour or startle display means any pattern of bluffing behaviour in an animal that lacks strong defences, such as suddenly displaying conspicuous eyespots, to scare off or momentarily distract a predator, thus giving the prey animal an opportunity to escape. The term deimatic or dymantic originates from the Greek δειματόω (deimatóo), meaning "to frighten".

<i>Animal Coloration</i> (book) 1892 book by Frank Evers Beddard

Animal Coloration, or in full Animal Coloration: An Account of the Principal Facts and Theories Relating to the Colours and Markings of Animals, is a book by the English zoologist Frank Evers Beddard, published by Swan Sonnenschein in 1892. It formed part of the ongoing debate amongst zoologists about the relevance of Charles Darwin's theory of natural selection to the observed appearance, structure, and behaviour of animals, and vice versa.

<span class="mw-page-title-main">Coloration evidence for natural selection</span> Early evidence for Darwinism from animal coloration

Animal coloration provided important early evidence for evolution by natural selection, at a time when little direct evidence was available. Three major functions of coloration were discovered in the second half of the 19th century, and subsequently used as evidence of selection: camouflage ; mimicry, both Batesian and Müllerian; and aposematism.

<span class="mw-page-title-main">Coincident disruptive coloration</span> Camouflage joining up separate parts of body

Coincident disruptive coloration or coincident disruptive patterns are patterns of disruptive coloration in animals that go beyond the usual camouflage function of breaking up the continuity of an animal's shape, to join up parts of the body that are separate. This is seen in extreme form in frogs such as Afrixalus fornasini where the camouflage pattern extends across the body, head, and all four limbs, making the animal look quite unlike a frog when at rest with the limbs tucked in.

<span class="mw-page-title-main">Distractive markings</span>

Distractive markings serve to camouflage animals or military vehicles by drawing the observer's attention away from the object as a whole, such as noticing its outline. This delays recognition. The markings necessarily have high contrast and are thus in themselves conspicuous. The mechanism therefore relies, as does camouflage as a whole, on deceiving the cognition of the observer, not in blending with the background.

<i>Dazzled and Deceived</i> Camouflage book by Peter Forbes

Dazzled and Deceived: Mimicry and Camouflage is a 2009 book on camouflage and mimicry, in nature and military usage, by the science writer and journalist Peter Forbes. It covers the history of these topics from the 19th century onwards, describing the discoveries of Henry Walter Bates, Alfred Russel Wallace and Fritz Müller, especially their studies of butterflies in the Amazon. The narrative also covers 20th-century military camouflage, begun by the painter Abbot Thayer who advocated disruptive coloration and countershading and continued in the First World War by the zoologist John Graham Kerr and the marine artist Norman Wilkinson, who developed dazzle camouflage. In the Second World War, the leading expert was Hugh Cott, who advised the British army on camouflage in the Western Desert.

In evolutionary biology, mimicry in vertebrates is mimicry by a vertebrate of some model, deceiving some other animal, the dupe. Mimicry differs from camouflage as it is meant to be seen, while animals use camouflage to remain hidden. Visual, olfactory, auditory, biochemical, and behavioral modalities of mimicry have been documented in vertebrates.

References

  1. 1 2 3 Cott 1940, p. 82.
  2. Thayer 1909, pp. 81–82.
  3. Newark, Tim (2007). Camouflage. Thames & Hudson. p. 33. ISBN   978-0-500-51347-7.
  4. Cott 1940, pp. 72–73.
  5. Cott 1940, p. 70.
  6. Cott 1940, p. 83.
  7. Cott 1940, p. 88.
  8. Cloudsley-Thompson, J. L. (1989). "Some Aspects of Camouflage in Animals (review article)" (PDF). Qatar University Science Bulletin (9): 141–158.
  9. 1 2 Caro 2005, p. 61.
  10. Barlow, G. W. (1972). "The attitude of fish eye-lines in relation to body shape and to stripes and bars". Copeia. 1972 (1): 4–12. doi:10.2307/1442777. JSTOR   1442777.
  11. Gavish, Leah; Gavish, Benjamin (1981). "Patterns that conceal a bird's eye". Zeitschrift für Tierpsychologie. 56 (3): 193–204. doi:10.1111/j.1439-0310.1981.tb01296.x.
  12. Machin, David (2014). Visual Communication. De Gruyter. p. 668. ISBN   978-3-11-025549-2.
  13. Kjernsmo, Karin; Merilaita, Sami (2013). "Eyespots divert attacks by fish". Proceedings of the Royal Society B: Biological Sciences. 280 (1766): 20131458. doi: 10.1098/rspb.2013.1458 . ISSN   0962-8452. PMC   3730605 . PMID   23864602.

Bibliography

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