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 many 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 animals 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.
The book
Approach
Adaptive Coloration in Animals is a 500-page book, in its first edition. It was published by Methuen (in London) and Oxford University Press (in New York) in 1940. It is full of detailed observations of types of camouflage and other uses of colour in animals, and illustrated by the author with clear drawings and photographs. There is a coloured frontispiece showing eight of Cott's paintings of tropical amphibians. The book has 48 monotone plates and several illustrations.Cott, 1940. Title page.
Cott's method is to provide a large number of examples, illustrated with his own drawings or photographs, showing animals from different groups including fish, reptiles, birds and insects, especially butterflies. The examples are chosen to illustrate specific adaptations. For example, the fish Chaetodon capistratus is described as follows:Cott, 1940. pp. 372-373.
Cott was well aware that he was publishing in wartime. There are, as Julian Huxley remarks in his 'Introduction', references throughout the book to the human analogues of animal camouflage and concealment. For example, in the section on 'Adaptive Silence', the kestrel is said to "practise dive-bombing attacks", or "after the fashion of a fighter 'plane" to fly down other birds, while "Owls have solved the problem of the silent air-raid"; Cott spends the rest of that paragraph on the "method which has recently been rediscovered and put into practice" of shutting off a bomber's engines and "gliding noiselessly down towards their victims" at Barcelona in the Spanish Civil War.Cott, 1940. p. 144. In the concluding chapter, Cott explicitly states "The innumerable visible devices used ... in peacetime and in wartime ... are merely rediscovered ... applications of colour that have already reached a high ... degree of specialization and perfection.. in the animal world", mentioning predator-prey relationships, sexual selection and signalling to rivals. He then compares the "hunting disguises put on ... as a means of approaching, ambushing or alluring game, and the sniping suits, concealed machine-gun posts, and booby traps" with the camouflage of animal predators; and similarly he compares "protective disguises" with the "photographer's hide and the gunner's observation post." In the same section, Cott compares intentionally visible signs with animal warning colours: "The policeman's white gloves have their parallel in the white stripes or spots of nocturnal skunks and carabids. The Automobile Association has adopted a system of coloration [black and yellow] whose copyright belongs by priority to wasps and salamanders."Cott, 1940. p. 436.
Structure The book addresses its subject under three main headings: concealment, advertisement, and disguise.
Part I: Concealment
The methods by which concealment is attained in nature
Cott sets out his view that we have to be re-taught how to see, mentioning Ruskin's "innocence of the eye". He argues that camouflage should, and in animals actually does, use four mechanisms: colour resemblance, obliterative shading (i.e. countershading, the graded shading which conceals self-shadowing of the lower body), disruptive coloration, and shadow elimination.
Chapter 1. General colour resemblance. Cott gives many examples such as a table of 16 species of green tropical tree-snakes.
Chapter 2. Variable colour resemblance. Caterpillars and pupae (as in Poulton's famous experiment) are coloured to match their environment. Mountain hares change colour in winter; many fish, cephalopods, frogs, and crustacea can change colour rapidly.
Chapter 3. Obliterative shading. Following the artist and amateur naturalist Abbott Handerson Thayer, Cott explains countershading with diagrams, photographs of models and examples of real animals. He shows how helpful it would be for military camouflage with drawings of gun barrels.
Chapter 4. Disruptive coloration. Cott argues with diagrams, drawings, photographs and examples that animals are often extremely effectively disruptively patterned. He analyses the component effects of disruption, including "differential blending" and "maximum disruptive contrast". Cott's figure 7 is a set of nine drawings, arranged as a 3x3 table. On the left is an animal's outline in grey tone against a differently coloured background. In the centre, the same animals are now disruptively patterned against the same plain backgrounds. On the right, the disruptively patterned animals are shown against realistic broken backgrounds containing vegetation or rocks. Cott explains
Cott goes on to explain that the right-hand drawing shows the effect "of broken surroundings in further blending and confusing the picture", observing that this is the closest to what is seen in nature. His readers are invited to look first at the right-hand images to gain an idea of the power of "these optical devices" as camouflage, putting off the moment when the animal is actually recognised.Cott, 1940. p. 53.
Chapter 5. Coincident disruptive coloration.
Animals such as frogs are patterned so that when they are at rest with legs tucked in, their outline is powerfully disrupted with markings that seem to flow across body and leg boundaries. Eyes too are often hidden in stripes or eye masks.
Chapter 6. Concealment Of the shadow. Cast shadows give away even well-camouflaged animals. Many animals therefore take care to minimise shadow, by lying down, with flattened bodies, or with fringes. Some hawkmoth caterpillars have false shadow patterns to suggest they are parts of other objects.
The function of concealing coloration in nature
Chapter 7. Concealment in defence, mainly as illustrated by birds. Cott considers how effective camouflage is as an adaptation, such as in incubation and rest (sleep) in birds. For instance nightjars are nocturnal, and rest, well camouflaged, on the ground during the day.
Chapter 8. Concealment In offence. Cott describes the care that predators take when approaching prey, minimizing visible movement and scent, the use of cover for ambush, and "adaptive silence".
Chapter 9. Objections and evidence bearing on the theory of concealing coloration. In this chapter Cott discusses various objections to the adaptive (evolutionary) nature of camouflage, and provides evidence to dismiss them. Some are "based upon such obvious fallacies that they hardly deserve serious consideration."
Chapter 10. The effectiveness of concealing coloration. Cott describes simple experiments such as that fish that have changed colour to match a pale background survived better (64% to 42%) on such a background than fish which had not. He also quotes some anecdotal observations on wild animals with similar but not quantified results.
Part II: Advertisement The methods by which conspicuousness is attained in nature
Chapter 1. The appearance and behaviour of aposematic animals. Animals that are genuinely distasteful (aposematic) boldly advertise themselves in black, white, red, and yellow. They are often "sluggish", not running from predators; gregarious; and diurnal, since warning displays only work if they can be seen "by potential enemies".Cott, 1940. p. 203.
Chapter 2. Warning displays. Aposematic animals often have (honest) threat displays; edible prey sometimes have (bluffing) startle displays. For example the frilled lizard, Chlamydosaurus kingii, is illustrated in a drawing by Cott, with its tail raised over the body, stretched up on all four legs, mouth wide open, and frills out both sides of the head, making it a startling sight.
Chapter 3. Adventitious warning coloration. Some marine animals select aposematic materials as coverings, not only as camouflage. Some birds nest near wasps' nests.
Warning coloration in relation to prey Chapter 4. The nature and function of warning coloration, as illustrated by the mammalia. Prey like porcupines have warning colours, make noise, and attack predators (even leopards).
Chapter 5. The Protective Attributes Of Aposematic Animals In General. Evidence is given that conspicuous animals such as caterpillars really are distasteful. Animals with actual poisons are discussed, and how these are secreted, used in bites and stings, or kept to make the animal bitter tasting.
Chapter 6. The relation between warning colours and distasteful attributes. Various kinds of evidence are presented for aposematism.
Chapter 7. The effectiveness of protective attributes associated with warning colours. Experimental evidence is presented that insects with warning colours are rejected by predators.
Warning coloration in reference to predatory enemies Chapter 8. Experimental evidence that vertebrate enemies learn by experience. Experiments by Cott show that toads learn to avoid eating stinging bees.
Chapter 9. Evidence of selective feeding by vertebrate enemies in a state of nature. Evidence from wild birds and toads demonstrates preferences for particular prey.
Part III: Disguise
Special protective and aggressive resemblance
Chapter 1. Special resemblance to particular objects. Cott describes leaf-like fish, chameleons, and insects, and other mimetic forms of camouflage. A liana-like snake near Para (a haunt of Henry Walter Bates in Naturalist on the River Amazons) 160 times as long as it was thick is called "a revelation in the art of aggressive resemblance".
Chapter 2. Adaptive behaviour in relation to special cryptic resemblance.