Countershading

Countershading, or Thayer's law, is a method of camouflage in which an animal's coloration is darker on the 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 predators and prey, and has occurred since at least the Cretaceous period.

When light falls from above on a uniformly coloured three-dimensional object such as a sphere, it makes the upper side appear lighter and the underside darker, grading from one to the other. This pattern of light and shade makes the object appear solid, and therefore easier to detect. The classical form of countershading, discovered in 1909 by the artist Abbott Handerson Thayer, works by counterbalancing the effects of self-shadowing, again typically with grading from dark to light. In theory this could be useful for military camouflage, but in practice it has rarely been applied, despite the best efforts of Thayer and, later, in the Second World War, of the zoologist Hugh Cott.

The precise function of various patterns of animal coloration that have been called countershading has been debated by zoologists such as Hannah Rowland (2009), with the suggestion that there may be multiple functions including flattening and background matching when viewed from the side; background matching when viewed from above or below, implying separate colour schemes for the top and bottom surfaces; outline obliteration from above; and a variety of other largely untested non-camouflage theories. A related mechanism, counter-illumination, adds the creation of light by bioluminescence or lamps to match the actual brightness of a background. Counter-illumination camouflage is common in marine organisms such as squid. It has been studied up to the prototype stage for military use in ships and aircraft, but it too has rarely or never been used in warfare.

The reverse of countershading, with the belly pigmented darker than the back, enhances contrast and so makes animals more conspicuous. It is found in animals that can defend themselves, such as skunks. The pattern is used both in startle or deimatic displays and as a signal to warn off experienced predators. However, animals that habitually live upside-down but lack strong defences, such as the Nile catfish and the Luna moth caterpillar, have upside-down countershading for camouflage.

Tiburón
Many animals, such as this grey reef shark, are countershaded.
Thayer Concealing-Coloration Plate XII - Luna Caterpillar a) in position b) inverted
Illustration from the artist Abbot Thayer's 1909 book on camouflage of a Luna caterpillar Actias luna
a) in position b) inverted.

Early research

Thayers ships
Thayer's 1902 patent application. He failed to convince the US Navy.

The English zoologist Edward Bagnall Poulton, author of The Colours of Animals (1890) discovered the countershading of various insects, including the pupa or chrysalis of the purple emperor butterfly, Apatura iris,[1] the caterpillar larvae of the brimstone moth, Opisthograptis luteolata [a] and of the peppered moth, Biston betularia.[b][2][3] However he did not use the term countershading, nor did he suggest that the effect occurred widely.[4]

White fowl lacking countershading
Thayer's "White fowl, lacking counter-shading, against a flat white cloth."
Abbott thayer countershading
A 1917 photograph of a countershading study by Thayer, who became obsessed by the mistaken idea that all animals are countershaded.[5] The model on the left is conventionally camouflaged and visible, whereas another on the right is so carefully countershaded that it is effectively invisible.[6]

The New Hampshire artist Abbott Handerson Thayer was one of the first to study and write about countershading. In his 1909 book Concealing-Coloration in the Animal Kingdom, he correctly described and illustrated countershading with photographs and paintings, but wrongly claimed that almost all animals are countershaded.[7] For this reason countershading is sometimes called Thayer's law. Thayer wrote:

Animals are painted by Nature darkest on those parts which tend to be most lighted by the sky's light, and vice versa. ... the fact that a vast majority of creatures of the whole animal kingdom wear this gradation, developed to an exquisitely minute degree, and are famous for being hard to see in their homes, speaks for itself.

— Thayer[8]

Thayer observed and painted a number of examples, including the Luna moth caterpillar Actias luna, both in its habitual upside-down feeding position, where its countershading makes it appear flat, and artificially inverted from that position, where sunlight and its inverted countershading combine to make it appear heavily shaded and therefore solid.[9] Thayer obtained a patent in 1902 to paint warships, both submarines and surface ships, using countershading,[10] but failed to convince the US Navy to adopt his ideas.[11]

Hugh Bamford Cott in his 1940 book Adaptive Coloration in Animals described many instances of countershading, following Thayer in general approach[12] but criticising Thayer's excessive claim ("He says 'All patterns and colors whatsoever of all animals that ever prey or are preyed upon are under certain normal circumstances obliterative.'") that effectively all animals are camouflaged with countershading. Cott called this "Thayer straining the theory to a fantastic extreme".[13]

Both Thayer and Cott included in their books photographs of a non-countershaded white cockerel against a white background, to make the point that in Thayer's words "a monochrome object can not be 'obliterated', no matter what its background"[14] or in Cott's words "Colour resemblance alone is not sufficient to afford concealment".[15] Cott explained that

Contrary to what might have been expected by any one lacking in artistic perception, the bird appears highly conspicuous, the back looking lighter, and the breast darker, than the background, although in actual fact, back, background and breast are all pure white."[16]

Application

In animals

Darga117
Ibexes are effectively flattened by countershading, making them nearly invisible against a desert background. There are three in the image.

Countershading is observed in a wide range of animal groups, both terrestrial, such as deer, and marine, such as sharks.[17] It is the basis of camouflage in both predators and prey.[18] It is used alongside other forms of camouflage including colour matching and disruptive coloration.[18] Among predatory fish, the gray snapper, Lutianus griseus, is effectively flattened by its countershading, while it hunts an "almost invisible" prey, the hardhead fish, Atherina laticeps which swims over greyish sands.[19] Other countershaded marine animals include blue shark, herring, and dolphin; while fish such as the mackerel and sergeant fish are both countershaded and patterned with stripes or spots.[20]

It tones the canvas on which are painted the Leopard's spots, the Tiger's stripes ... It is the dress almost universally worn by rodents... It is the essential uniform adopted by Conies, Asses, Antelopes, Deer ... It is repeated extensively among the marsupials ... It provides a basic livery for the great majority of snakes, lizards, and amphibians. Among insects it reaches a fine state of perfection in different caterpillars and grasshoppers. ... It is, however, in rivers, and in the surface waters of the sea, that countershading reaches its maximum development and significance.

— Hugh Cott[18]

Countershading existed in marine reptiles in the Cretaceous period. Fossilised skin pigmented with dark-coloured eumelanin reveals that both leatherback turtles and mosasaurs had dark backs and light bellies.[21] The ornithischian dinosaur Psittacosaurus similarly appears to have been countershaded, implying that its predators detected their prey by deducing shape from shading. Modelling suggests further that the dinosaur was optimally countershaded for a closed habitat such as a forest.[22]

A related mechanism: counter-illumination

Another form of animal camouflage uses bioluminescence to increase the average brightness of an animal to match the brightness of the background.[23] This is called counter-illumination. It is common in mid-water pelagic fish and invertebrates especially squid. It makes the counter-illuminated animal practically invisible to predators viewing it from below.[24] As such, counter-illumination camouflage can be seen as an extension beyond what countershading can achieve. Where countershading only paints out shadows, counter-illumination can add in actual lights, permitting effective camouflage in changing conditions, including where the background is bright enough to make an animal that is not counter-illuminated appear as a shadow.[25]

Military

Countershaded Rail-mounted Gun Camouflaged by Hugh Cott 1940
Countershaded rail-mounted guns camouflaged by Hugh Cott (above) and in conventional style (below), August 1940. The British authorities agreed Cott's countershading worked, but refused to adopt it.[26]

Countershading, like counter-illumination, has rarely been applied in practice for military camouflage, though not because military authorities were unaware of it. Both Abbott Thayer in the First World War and Hugh Cott in the Second World War proposed countershading to their countries' armed forces. They each demonstrated the effectiveness of countershading, without succeeding in persuading their armed forces to adopt the technique, though they influenced military adoption of camouflage in general.[11]

Cott was a protege of John Graham Kerr who had quarrelled with Norman Wilkinson in the First World War about dazzle camouflage for ships. Wilkinson remained influential in 1939 as an inspector of camouflage, so a political argument developed. Cott was invited to camouflage a 12-inch rail-mounted gun, alongside a similar gun camouflaged conventionally. Cott carefully combined disruptive contrast to break up the gun barrel's outlines with countershading to flatten out its appearance as a solid cylinder. The guns were then photographed from the air from various angles, and in Peter Forbes's view "the results were remarkable."[27] Cott's gun is "invisible except to the most minute scrutiny by someone who knows exactly where to look and what to look for. The other gun is always highly visible." The authorities hesitated, appearing to be embarrassed by the evidence that Cott was right, and argued that countershading would be too difficult to use as an expert zoologist would be needed to supervise every installation. Cott was posted to the Middle East, and Kerr unsuccessfully intervened, pleading for guns to be painted Cott's way and Cott to be brought home.[26]

Sherman Firefly 9-08-2008 15-05-43
A preserved Sherman Firefly (2008); its gun barrel is painted with a pattern that combines countershading and outline disruption to disguise its length.

The Australian zoologist William Dakin in his 1941 book The Art of Camouflage followed Thayer in describing countershading in some detail, and the book was reprinted as a military handbook in 1942. Dakin photographed model birds, much as Thayer and Cott had done, and argued that the shoulders and arms of battledress should be countershaded.[28]

Countershading was described in the US War Department's 1943 Principles of Camouflage, where after four paragraphs of theory and one on its use in nature, the advice given is[29]

Upper surfaces should be painted and textured so as to conform to the color and tone of the surrounding country (background) and the sides graded and toned from this to the white which the under surfaces and parts in shade should be painted.[29]

Focke-Wulf Fw 190D-9 outside USAF
True (graduated from dark to light) countershaded Focke-Wulf Fw 190 D-9

Inventors have continued to advocate military usage of countershading, with for example a 2005 US patent for personal camouflage including countershading in the form of "statistical countercoloring" with varying sizes of rounded dark patches on a lighter ground.[30]

Research by Ariel Tankus and Yehezkel Yeshurun investigating "camouflage breaking", the automated detection of objects such as tanks, showed that analysing images for convexity by looking for graded shadows can "break very strong camouflage, which might delude even human viewers." More precisely, images are searched for places where the gradient of brightness crosses zero, such as the line where a shadow stops becoming darker and starts to become lighter again. The technique defeated camouflage using disruption of edges, but the authors observed that animals with Thayer countershading are using "counter-measures to convexity based detectors", which implied "predators who use convexity based detectors."[31]

Function

Countershading
Countershading acts as a form of camouflage by 'painting out' the self-shadowing of the body or object. The result is a 'flat' appearance, instead of the 'solid' appearance (with visual convexity) of the body before countershading.

Hannah Rowland, reviewing countershading 100 years after Abbott Thayer, observed that countershading, which she defines as "darker pigmentation on those surfaces exposed to the most lighting" is a common but poorly understood aspect of animal coloration.[4] She noted there had been "much debate" about how countershading works.[32] She considered the evidence for Thayer's theory that this acts as camouflage "by reducing ventral shadowing", and reviewed alternative explanations for countershading.[4]

Camouflage theories of countershading, Rowland wrote, include "self-shadow concealment which results in improved background matching when viewed from the side"; "self-shadow concealment that flattens the form when viewed from the side"; "background matching when viewed from above or below"; and "body outline obliteration when viewed from above".[4] These are examined in turn below.

Flattening and background matching when viewed from the side

Eastern Gray Squirrel 800
When oriented horizontally, the countershading of the gray squirrel, Sciurus carolinensis, helps to "paint out" its ventral shadow.
Sciurus carolinensis-gotigersjf (cropped)
When oriented vertically, the gray squirrel's pale belly is conspicuous rather than camouflaged.

Cott, like Thayer, argued that countershading would make animals hard to see from the side, as they would "fade into a ghostly elusiveness".[33] Rowland notes that Cott is here reviewing Thayer's theory and "reinforcing the view that a gradation in shading would act to eliminate the effects of ventral shadowing."[4] Kiltie measured the effect of the countershading of the grey squirrel, Sciurus carolinensis, showing that when the squirrel is horizontal the self-shadowing of the belly is partly concealed, but that when the squirrel is vertical (as when climbing a tree trunk) this effect did not occur.[34]

Thayer's original argument, restated by Cott,[33] was that nature did the exact opposite with countershading that an artist did with paint when creating the illusion of solid three-dimensionality, namely counteracting the effect of shade to flatten out form. Shading is a powerful cue used by animals in different phyla to identify the shapes of objects. Research with chicks showed that they preferred to peck at grains with shadows falling below them (as if illuminated from above), so both humans and birds may make use of shading as a depth cue.[4][35]

Background matching from above or below

Scomber scombrus
The mackerel, Scomber scombrus, like many pelagic fish, is dark above, pale below, camouflaging it against the ocean depths and the bright surface.[c]

A completely different function of animal (and military vehicle) coloration is to camouflage the top and bottom surfaces differently, to match their backgrounds below and above respectively. This was noted, for example, by Frank Evers Beddard in 1892:

Among pelagic fish it is common to find the upper surface dark-coloured and the lower surface white, so that the animal is inconspicuous when seen either from above or below.

— Frank Evers Beddard[36]
Grumman F6F-5K Hellcat (G-50) AN0622498
Top/bottom countershaded[d] Grumman F6F Hellcat

Early researchers including Alfred Russel Wallace,[37] Beddard,[38] Cott[39] and Craik[40] argued that in marine animals including pelagic fish such as marlin and mackerel, as well as dolphins, sharks, and penguins the upper and lower surfaces are sharply distinct in tone, with a dark upper surface and often a nearly white lower surface. They suggested that when seen from the top, the darker dorsal surface of the animal would offer camouflage against the darkness of the deep water below. When seen from below, the lighter ventral area would similarly provide the least possible contrast with the sunlit ocean surface above.[4] There is some evidence for this in birds, where birds that catch fish at a medium depth, rather than at the surface or on the seabed, are more often coloured in this way, and the prey of these birds would see only the underside of the bird.[41] Rowland concluded that each possible role for coloration patterns lumped together as "countershading" needs to be evaluated separately, rather than just assuming it functions effectively.[4]

Outline obliteration from above

Rowland (2009) identified an additional mechanism of countershading not previously analysed, namely that a round body such as a cylinder illuminated and seen from above appears to have dark sides. Using a graphics tool, she demonstrated that this effect can be flattened out by countershading. Since predators are known to use edges to identify prey, countershading may therefore, she argues, make prey harder to detect when seen from above.[4]

Non-camouflage theories

Non-camouflage theories include protection from ultraviolet light; thermoregulation; and protection from abrasion. All three of these "plausible" theories remained largely untested in 2009, according to Rowland.[4]

Evidence

Glaucus atlanticus 1 cropped
The sea slug Glaucus atlanticus swims and is countershaded upside-down.

Despite demonstrations and examples adduced by Cott and others, little experimental evidence for the effectiveness of countershading was gathered in the century since Thayer's discovery. Experiments in 2009 using artificial prey showed that countershaded objects do have survival benefits[42] and in 2012, a study by William Allen and colleagues showed that countershading in 114 species of ruminants closely matched predictions for "self-shadow concealment", the function predicted by Poulton, Thayer and Cott.[43]

Mechanism

Evolutionary developmental biology has assembled evidence from embryology and genetics to show how evolution has acted at all scales from the whole organism down to individual genes, proteins and genetic switches. In the case of countershaded mammals with dark (often brownish) upper parts and lighter (often buff or whitish) under parts, such as in the house mouse, it is the Agouti gene which creates the difference in shading. Agouti encodes for a protein, the Agouti signalling peptide (ASP), which specifically inhibits the action of the Melanocortin 1 receptor (MC1R). In the absence of the Agouti protein, alpha-melanocyte-stimulating hormone stimulates the cells bearing MC1R, melanocytes, to produce dark eumelanin, colouring the skin and fur dark brown or black. In the presence of the Agouti protein, the same system produces the lighter-coloured, yellow or red phaeomelanin. A genetic switch active in the cells of the embryo that will become the belly skin causes the Agouti gene to become active there, creating the countershading seen in adult mammals.[44]

Reverse countershading

Honey badger
The honey badger is reverse countershaded, a form of aposematism (warning coloration).

If countershading paints out shadows, the reverse, darkening the belly and lightening the back, would maximise contrast by adding to the natural fall of light. This pattern of animal coloration is found in animals such as the skunk and honey badger with strong defences—the offensive stink of the skunk, and the sharp claws, aggressive nature and stink of the honey badger.[45] These animals do not run when under attack, but move slowly, often turning to face the danger, and giving deimatic or threat displays either to startle inexperienced predators, or as an aposematic signal, to warn off experienced ones.[46]

The caterpillar of the Luna moth, as discovered by Thayer, is in Cott's phrase "countershaded in relation to [its] attitude", i.e. shaded with a light back grading to a dark belly, as is the Nile catfish, Synodontis batensoda for the same reason: these animals (and other caterpillars including Automeris io and the eyed hawkmoth, Smerinthus ocellatus) habitually live 'upside down' with the belly uppermost. Similarly in the sea slug Glaucus atlanticus, the reverse countershading is associated with inverted habits. These animals are thus employing countershading in the usual way for camouflage.[47]

Examples in animals

Tragelaphus scriptus (male)

Bushbuck, Tragelaphus scriptus, appears almost perfectly even in tone, showing that its countershading has cancelled out its self-shading. The white spots and markings help to disrupt the 'solidity' of the animal further.

Sylvia borin (Örebro County)

Many birds, such as this garden warbler, Sylvia borin, are countershaded. The lighter belly makes the bird appear almost evenly coloured when seen from the side.

Carolina anole

The Carolina anole lizard, Anolis caroliensis, is smoothly countershaded.

Adelie Penguin2

Adelie penguins, Pygoscelis adeliae, are white below and dark above, presumably to enable them to blend with the sea surface when seen from below, and with deep water when seen from above.

Smerinthus ocellatus caterpillar on apple tree

The caterpillar larva of the eyed hawkmoth, Smerinthus ocellatus, is reverse countershaded, making it appear flat when upside-down in feeding position.

Eyed hawkmoth larvae reverse countershaded

When the eyed hawkmoth caterpillar is turned upright, as here, its countershading adds to the shading caused by sunlight, rather than "painting it out", so its body appears strongly rounded in this position.

Striped Skunk (Mephitis mephitis) DSC 0030

Striped skunk, Mephitis mephitis, has conspicuous warning coloration with reversed countershading, alerting predators to its powerfully defensive stink.

Axis axis (Nagarhole, 2010)

Chital deer, Axis axis. The animals in the background are effectively countershaded with their bodies horizontal, but the upright stag in the foreground is made conspicuous by its light belly. The spotting is disruptive.

See also

Notes

  1. ^ It was called Rumia crataegata at the time.
  2. ^ It was called Amphidasis betularia at the time.
  3. ^ The mackerel, like many other pelagic fish, is also camouflaged by silvering, and when seen from above it has a bold disruptive pattern.
  4. ^ Colours used are Non-Specular Sea Blue, Intermediate Blue, White.

References

  1. ^ Poulton, 1888.
  2. ^ Poulton, 1887.
  3. ^ Thayer, 1909. p 22.
  4. ^ a b c d e f g h i j Rowland, 2009.
  5. ^ Forbes, 2009. pp. 76–79.
  6. ^ Behrens, 2009.
  7. ^ Thayer, 1909.
  8. ^ Thayer, 1909. pp 14–15.
  9. ^ Thayer, 1909. Plate XII.
  10. ^ U.S. Patent 715,013
  11. ^ a b Goldstein, 2009, pp. 233–235.
  12. ^ Cott, 1940. pp. 35–46.
  13. ^ Cott, 1940. pp. 172–173.
  14. ^ Thayer, 1909. Caption to Figure 7.
  15. ^ Cott, 1940. Caption to Plate 7.
  16. ^ Cott, 1940. p. 35.
  17. ^ ONR, 2013.
  18. ^ a b c Cott, 1940. p. 40.
  19. ^ Cott, 1940. p37.
  20. ^ Cott, 1940. p41
  21. ^ Lindgren, Johan and Peter Sjövall, Ryan M. Carney, Per Uvdal, Johan A. Gren, Gareth Dyke, Bo Pagh Schultz, Matthew D. Shawkey, Kenneth R. Barnes, Michael J. Polcyn (February 2014). "Skin pigmentation provides evidence of convergent melanism in extinct marine reptiles". Nature. 506 (7489): 484–488. doi:10.1038/nature12899. PMID 24402224.CS1 maint: Uses authors parameter (link)
  22. ^ Vinther, Jakob; Nicholls, Robert; Lautenschlager, Stephan; Pittman, Michael; Kaye, Thomas G.; Rayfield, Emily; Mayr, Gerald; Cuthill, Innes C. (2016). "3D Camouflage in an Ornithischian Dinosaur". Current Biology. 26: 1–7. doi:10.1016/j.cub.2016.06.065. PMC 5049543.
  23. ^ Young and Roper, 1977.
  24. ^ Young and Roper, 1976.
  25. ^ Jones, 2004. p. 1151.
  26. ^ a b Forbes, 2009. pp. 142–146, 149–151, 156.
  27. ^ Forbes, 2009. p. 150.
  28. ^ Elias, 2011.
  29. ^ a b Anon, 1943.
  30. ^ Tooley, 2005.
  31. ^ Tankus and Yeshurun, 2013.
  32. ^ Rowland, 2011.
  33. ^ a b Cott, 1940. pp 36–37.
  34. ^ Kiltie, 1944.
  35. ^ Hershberger, 1970.
  36. ^ Beddard, 1892. p. 122.
  37. ^ Wallace, 1889, p 193
  38. ^ Beddard, 1895, p 115
  39. ^ Cott, 1940.
  40. ^ Craik, 1944.
  41. ^ Ruxton 2004.
  42. ^ Rowland et al, 2009.
  43. ^ Allen et al, 2012.
  44. ^ Carroll, Sean B. (2006). Endless Forms Most Beautiful. Weidenfeld and Nicolson. pp. 229–231, 237. ISBN 978-0-297-85094-6.
  45. ^ "Black, White and Stinky: Explaining Coloration in Skunks and Other Boldly Colored Animals". University of Massachusetts Amherst. 27 May 2011. Retrieved 19 June 2014.
  46. ^ Edmunds, 2008.
  47. ^ Cott, 1940. p. 43.

Bibliography

Pioneering books

General reading

  • Behrens, Roy R. (2009). Goldstein, E Bruce (ed.). Encyclopedia of Perception, Volume 1. Sage. pp. 233–235.
  • Edmunds, Malcolm (2008). "Deimatic Behavior". In Capinera, John L. (ed.). Encyclopedia of Entomology. Springer.
  • Forbes, Peter (2009). Dazzled and Deceived: Mimicry and Camouflage. Yale.
  • Rowland, Hannah M. (2011). "The history, theory and evidence for a cryptic function of countershading". In Stevens, Martin; Merilaita, Sami (eds.). Animal Camouflage: Mechanisms and Function. Cambridge University Press.
  • Ruxton, Graeme D.; Sherratt, Thomas N.; Speed, Michael P. (2004). "3. Countershading and counterillumination". Avoiding Attack: The Evolutionary Ecology of Crypsis, Warning Signals and Mimicry. Oxford University Press.

Journals

Abbott Handerson Thayer

Abbott Handerson Thayer (August 12, 1849 – May 29, 1921) 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 the major American art collections. He is perhaps best known for his 'angel' paintings, some of which use his children as models.

During the last third of his life, he worked together with his son, Gerald Handerson Thayer, on a book about protective coloration in nature, titled Concealing-Coloration in the Animal Kingdom. First published by Macmillan in 1909, then reissued in 1918, it may have had an effect on military camouflage during World War I. However it was roundly mocked by Theodore Roosevelt and others for its assumption that all animal coloration is cryptic.Thayer also influenced American art through his efforts as a teacher, training apprentices in his New Hampshire studio.

Adaptive Coloration in Animals

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.

The book's general method is to present a wide range of examples from across the animal kingdom of each type of coloration, including marine invertebrates and fishes as well as terrestrial insects, amphibians, reptiles, birds and mammals. The examples are supported by a large number of Cott's own drawings, diagrams, and photographs. This essentially descriptive natural history treatment is supplemented with accounts of experiments by Cott and others. The book had few precedents, but to some extent follows (and criticises) Abbott Handerson Thayer's 1909 Concealing-Coloration in the Animal Kingdom.

The book is divided into three parts: concealment, advertisement, and disguise. Part 1, concealment, covers the methods of camouflage, which are colour resemblance, countershading, disruptive coloration, and shadow elimination. The effectiveness of these, arguments for and against them, and experimental evidence, are described. Part 2, advertisement, covers the methods of becoming conspicuous, especially for warning displays in aposematic animals. Examples are chosen from mammals, insects, reptiles and marine animals, and empirical evidence from feeding experiments with toads is presented. Part 3, disguise, covers methods of mimicry that provide camouflage, as when animals resemble leaves or twigs, and markings and displays that help to deflect attack or to deceive predators with deimatic displays. Both Batesian mimicry and Müllerian mimicry are treated as adaptive resemblance, much like camouflage, while a chapter is devoted to the mimicry and behaviour of the cuckoo. The concluding chapter admits that the book's force is cumulative, consisting of many small steps of reasoning, and being a wartime book, compares animal to military camouflage.

Cott's textbook was at once well received, being admired both by zoologists and naturalists and among allied soldiers. Many officers carried a copy of the book with them in the field. Since the war it has formed the basis for experimental investigation of camouflage, while its breadth of coverage and accuracy have ensured that it remains frequently cited in scientific papers.

Aircraft camouflage

Aircraft camouflage is the use of camouflage on military aircraft to make them more difficult to see, whether on the ground or in the air. Given the possible backgrounds and lighting conditions, no single scheme works in every situation. A common approach has been a form of countershading, the aircraft being painted in a disruptive pattern of ground colors such as green and brown above, sky colors below. For faster and higher-flying aircraft, sky colors have sometimes been used all over, while helicopters and fixed-wing aircraft used close to the ground are often painted entirely in ground camouflage. Aircraft flying by night have often been painted black, but this actually made them appear darker than the night sky, leading to paler night camouflage schemes. There are trade-offs between camouflage and aircraft recognition markings, and between camouflage and weight. Accordingly, visible light camouflage has been dispensed with when air superiority was not threatened or when no significant aerial opposition was anticipated.

Aircraft were first camouflaged during World War I; aircraft camouflage has been widely employed since then. In World War II, disruptive camouflage became widespread for fighters and bombers, sometimes combined with countershading. Some air forces such as the German Luftwaffe varied their paint schemes to suit differing flight conditions such as the skyglow over German cities, or the sands of the Mediterranean front.

During and after World War II, the Yehudi lights project developed counter-illumination camouflage using lamps to increase the brightness of the aircraft to match the brightness of the sky. This was abandoned with improvements in radar, which seemed to render visible light camouflage redundant. However, aircraft continue to be painted in camouflage schemes; recent experiments have again explored active camouflage systems which allow colors, patterns and brightness to be changed to match the background, and some air forces have painted their fighters in digital camouflage patterns. Stealth technology, as in the Lockheed F-117 Nighthawk, aims to minimize an aircraft's radar cross-section and infrared signature, effectively providing multi-spectral camouflage at the price of reduced flying performance. Stealth may extend to avoiding or preventing vapor contrails.

Brimstone moth

The brimstone moth (Opisthograptis luteolata) is a moth of the family Geometridae. The species was first described by Carl Linnaeus in his 1758 10th edition of Systema Naturae.

Camouflage

Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see (crypsis), or by disguising them as something else (mimesis). 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. 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.

Military camouflage was spurred by the increasing range and accuracy of firearms in the 19th century. In particular the replacement of the inaccurate musket with the rifle made personal concealment in battle a survival skill. In the 20th century, military camouflage developed rapidly, especially during the First World War. On land, artists such as André Mare designed camouflage schemes and observation posts disguised as trees. At sea, merchant ships and troop carriers were painted in dazzle patterns that were highly visible, but designed to confuse enemy submarines as to the target's speed, range, and heading. During and after the Second World War, a variety of camouflage schemes were used for aircraft and for ground vehicles in different theatres of war. The use of radar since the mid-20th century has largely made camouflage for fixed-wing military aircraft obsolete.

Non-military use of camouflage includes making cell telephone towers less obtrusive and helping hunters to approach wary game animals. Patterns derived from military camouflage are frequently used in fashion clothing, exploiting their strong designs and sometimes their symbolism. Camouflage themes recur in modern art, and both figuratively and literally in science fiction and works of literature.

Concealing-Coloration in the Animal Kingdom

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.

The book, illustrated artistically by Abbott Thayer, sets out the controversial thesis that all animal coloration has the evolutionary purpose of camouflage. Thayer rejected Charles Darwin's theory of sexual selection, arguing in words and paintings that even such conspicuous animal features as the peacock's tail or the brilliant pink of flamingoes or roseate spoonbills were effective as camouflage in the right light.

The book introduced the concepts of disruptive coloration to break up an object's outlines, of masquerade, as when a butterfly mimics a leaf, and especially of countershading, where an animal's tones make it appear flat by concealing its self-shadowing.

The book was criticised by big game hunter and politician Theodore Roosevelt for its central assertion that every aspect of animal coloration is effective as camouflage. Roosevelt's detailed reply attacked the biased choice of examples to suit Abbott Thayer's thesis and the book's reliance on unsubstantiated claims in place of evidence. The book was more evenly criticised by zoologist and camouflage researcher Hugh Cott, who valued Thayer's work on countershading but regretted his overenthusiastic attempts to explain all animal coloration as camouflage. Thayer was mocked to a greater or lesser extent by other scientific reviewers.

Counter-illumination

Counter-illumination is a method of active camouflage seen in marine animals such as firefly squid and midshipman fish, and in military prototypes, producing light to match their backgrounds in both brightness and wavelength.

Marine animals of the mesopelagic (mid-water) zone tend to appear dark against the bright water surface when seen from below. They can camouflage themselves, often from predators but also from their prey, by producing light with bioluminescence photophores on their downward-facing surfaces, reducing the contrast of their silhouettes against the background. The light may be produced by the animals themselves, or by symbiotic bacteria, often Aliivibrio fischeri. Counter-illumination differs from countershading, which uses only pigments such as melanin to reduce the appearance of shadows. It is one of the dominant types of aquatic camouflage, along with transparency and silvering. All three methods make animals in open water resemble their environment.

Counter-illumination has not so far come into widespread military use, but during the Second World War it was trialled in ships in the Canadian Diffused lighting camouflage project, and in aircraft in the American Yehudi lights project.

Dazzle camouflage

Dazzle camouflage, also known as razzle dazzle (in the U.S.) or dazzle painting, was a family of ship camouflage used extensively in World War I, and to a lesser extent in World War II and afterwards. Credited to the British marine artist Norman Wilkinson, though with a rejected prior claim by the zoologist John Graham Kerr, it consisted of complex patterns of geometric shapes in contrasting colours, interrupting and intersecting each other.

Unlike other forms of camouflage, the intention of dazzle is not to conceal but to make it difficult to estimate a target's range, speed, and heading. Norman Wilkinson explained in 1919 that he had intended dazzle primarily to mislead the enemy about a ship's course and so to take up a poor firing position.Dazzle was adopted by the Admiralty in the UK, and then by the United States Navy. Each ship's dazzle pattern was unique to avoid making classes of ships instantly recognisable to the enemy. The result was that a profusion of dazzle schemes was tried, and the evidence for their success was at best mixed. So many factors were involved that it was impossible to determine which were important, and whether any of the colour schemes were effective.

Dazzle attracted the notice of artists such as Picasso, who claimed that Cubists like himself had invented it. Edward Wadsworth, who supervised the camouflaging of over 2,000 ships during the First World War, painted a series of canvases of dazzle ships after the war, based on his wartime work. Arthur Lismer similarly painted a series of dazzle ship canvases.

Dazzled and Deceived

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.

The book was well received by critics, both military historians and biologists, and won the 2011 Warwick Prize for Writing.

Disruptive coloration

Disruptive coloration (also known as disruptive camouflage or disruptive patterning) 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.

The importance of high-contrast patterns for successful disruption was predicted in general terms by the artist Abbott Thayer in 1909 and explicitly by the zoologist Hugh Cott in 1940. Later experimental research has started to confirm these predictions. Disruptive patterns work best when all their components match the background.

While background matching works best for a single background, disruptive coloration is a more effective strategy when an animal or a military vehicle may have a variety of backgrounds.

Conversely, poisonous or distasteful animals that advertise their presence with warning coloration (aposematism) use patterns that emphasize rather than disrupt their outlines. For example, skunks, salamanders and monarch butterflies all have high-contrast patterns that display their outlines.

Dun gene

The dun gene is a dilution gene that affects both red and black pigments in the coat color of a horse. The dun gene lightens most of the body while leaving the mane, tail, legs, and primitive markings the shade of the undiluted base coat color. A dun horse always has a dark dorsal stripe down the middle of its back, usually has a darker face and legs, and may have transverse striping across the shoulders or horizontal striping on the back of the forelegs. Body color depends on the underlying coat color genetics. A classic "bay dun" is a gray-gold or tan, characterized by a body color ranging from sandy yellow to reddish brown. Duns with a chestnut base may appear a light tan shade, and those with black base coloration are a steel gray. Manes, tails, primitive markings, and other dark areas are usually the shade of the undiluted base coat color. The dun gene may interact with all other coat color alleles.

Erebus ephesperis

Erebus ephesperis is a moth of the family Erebidae first described by Jacob Hübner in 1827. It is found in Asia, including India, Japan, the Korean Peninsula, China, Singapore and Borneo.

The wingspan is about 90 mm and the patterning is very obliterative, breaking the body outline with shadow like countershading.

Adults feed on fruit juice, including peach.

Glaucus atlanticus

Glaucus atlanticus (common names include the sea swallow, blue angel, blue glaucus, blue dragon, blue sea slug and blue ocean slug) is a species of small, blue sea slug, a pelagic aeolid nudibranch, a shell-less gastropod mollusk in the family Glaucidae.These sea slugs are pelagic: they float upside down by using the surface tension of the water to stay up, where they are carried along by the winds and ocean currents. Glaucus atlanticus makes use of countershading: the blue side of their body faces upwards, blending in with the blue of the water. The silver/grey side of the sea slugs faces downwards, blending in with the sunlight reflecting on the ocean's surface when viewed upwards underwater.

Glaucus atlanticus feeds on other pelagic creatures, including the Portuguese man o' war and other venomous siphonophores. This sea slug stores stinging nematocysts from the siphonophores within its own tissues as defense against predation. Humans handling the slug may receive a very painful and potentially dangerous sting.

List of camouflage methods

Camouflage is the concealment of animals or objects of military interest by any combination of methods that helps them to remain unnoticed. This includes the use of high-contrast disruptive patterns as used on military uniforms, but anything that delays recognition can be used as camouflage. Camouflage involves deception, whether by looking like the background or by resembling something else, which may be plainly visible to observers. This article lists methods used by animals and the military to escape notice.

Pangaré

Pangaré is a coat trait found in some horses that features pale hair around the eyes and muzzle and underside of the body. These pale areas can extend up to the flanks, throat and chest, behind the elbows, in front of the stifle, and up the buttock. Animals with the pangaré trait are sometimes called "mealy" or "light-pointed". The color of these lighter areas depends on the underlying color and ranges from off-white to light tan. This type of coloration is most often found in primitive breeds like the Fjord horse, Exmoor Pony, American Belgian Draft, and Haflinger. Wild equids like the Przewalski's Horse, Onager, African Wild Ass, Kiang as well as the domestic Donkey exhibit pangaré as a rule. Pangaré is thought to be a type of protective countershading.

Horse foals are often born with "foal pangaré" or light points, especially over black haired areas, which they lose when they shed their foal coats.

Dr. Phillip Sponenberg suggested that the seal brown coat color was caused by the action of pangaré on a black coat. However, seal brown horses have since tested negative for the recessive black genotype.

Chestnut horses with pangaré are sometimes called "Belgian sorrels".

Primitive markings

Primitive markings are a group of hair coat markings and qualities seen in several equine species, including horses, donkeys, and asses. In horses, they are associated with primitive breeds, though not limited to such breeds. The markings are particularly associated with the dun coat color family. All dun horses possess at least the dorsal stripe, but the presence of the other primitive markings varies. Other common markings may include horizontal striping on the legs, transverse striping across the shoulders, and lighter guard hairs along the edges of a dark mane and tail.

Shark anatomy

Shark anatomy differs from that of bony fish in a variety of ways. Variation observed within shark anatomy is a potential result of speciation and habitat variation

Sooty (gene)

A horse coat color that has the sooty trait is characterized by black or darker hairs mixed into a horse's coat, typically concentrated along the topline of the horse and less prevalent on the underparts. Sootiness is presumed to be an inherited trait, though the precise genetic mechanism, or series of mechanisms, is not well understood.

In most cases, sooty coats exhibit pronounced countershading; the dorsal region is darker than the ventral region. However, some forms seem to produce darker lower parts. The "false dorsal" or "countershading dorsal" can mimic the dorsal stripe associated with dun horses and is associated with the sooty trait. The most extensive expression of sooty produces a dark, often-dappled cast oriented down from the topline. Many horses with the sooty trait have a darker mask on the bony parts of the face.

It was once thought that the sooty trait was responsible for turning chestnut into liver chestnut, however it is not known to evenly darken the coat. The sooty trait is responsible for many dark bays and has a particularly pronounced effect on buckskins and palominos.

Although this trait has been called the "sooty gene", similar coat-darkening conditions studied in mice suggest that coat darkening is a polygenic trait. Just as in horses, the degree of sootiness in mice varies widely; some individuals have darker hairs that form a dorsal line, while others have extensive sootiness throughout. A statistical analysis of 1369 offspring of five Franches-Montagnes stallions indicated that darker shades of chestnut and bay might follow a recessive mode of inheritance.Horses without any sooty effect are termed "clear-coated."

Underwater camouflage

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.

Camouflage in large bodies of water differs markedly from camouflage on land. The environment is essentially the same on all sides. Light always falls from above, and there is generally no variable background to compare with trees and bushes. Three main camouflage methods predominate in water: transparency, reflection, and counter-illumination. Transparency and reflectivity are most important in the top 100 metres of the ocean; counter-illumination is the main method from 100 metres down to 1000 metres; while camouflage becomes less important in the dark waters below 1000 metres.

Camouflage in relatively shallow waters is more like terrestrial camouflage, where additional methods are used by many animals. For example, self-decoration is employed by decorator crabs; mimesis by animals such as the leafy sea dragon; countershading by many fish including sharks; distraction with eyespots by many fish; active camouflage through ability to change colour rapidly in fish such as the flounder, and cephalopods including octopus, cuttlefish, and squid.

Methods
In nature
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Patterns of evolution
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Vision in animals
Vision
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Evolution
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