Animal coloration

“ There is one other point regarding the protection afforded by colour to large mammals against carnivorous foes which I think has not been sufficiently considered by naturalists, and that is, that no matter how well the colour of an animal may harmonise with its surroundings as long as it remains perfectly still, as soon as it moves "it jumps to the eyes," as the French say, no matter what its colour may be. What is called protective coloration to be effective must be motionless. Movement, even very slight movement, at once destroys its efficacy. ”

“ The very frequent superiority of the male bird or insect in brightness or intensity of colour, even when the general coloration is the same in both sexes, now seems to me to be, primarily, due to the greater vigour and activity and the higher vitality of the male. The colours of an animal usually fade during disease or weakness, while robust health and vigour adds to their intensity. ”

“ We need not repeat the fabulous stories told about these color-changes: the facts which can be strictly verified by direct observation are wonderful enough without the adornments of imagination. These changes of color range from whity-yellow, through yellow, bright and dark green, to dull black; and these diversities of coloration may affect the entire surface of the animal, or one or other of its sides, or may appear only in spots. When the chameleon is asleep, and not exposed to the direct rays of the sun, its color is a whity-yellow ”

“ Now green is a very rare colour among mammals, and there ought therefore to be some special reason for its development in the Sloths. And, as a matter of fact, the means by which this coloration is produced is one of the most marvellous phenomena in the whole animal kingdom—so marvellous, indeed, that it is at first almost impossible to believe that it is true. ”

“ The examples given above show how natural selection may lead to the evolution of distinctive forms of coloration which are advantageous to the Fish either for concealment, aggression, or protection, and in conclusion it may be pointed out that by the same cause colour may be eliminated or its development checked if in any way harmful to the animal ”

“ No one has yet shown any principles which will better explain the great color scheme of the animal world, and until such explanation is forthcoming I believe it will not be wise for us to discard the idea of protective coloration. ”

“ We have further the dusky hue of creatures that haunt the night, such as mice, moles, and bats; and the gorgeous tints of fishes that swim among the coral reefs. These local color adaptations of animals are of great use to them, either enabling them to escape the notice of their enemies or to come upon their prey with the least risk of being detected. Certain groups of animals have a local color-adaptation, and may be noticed under the heading of Protective Coloration ”

“ Now in domesticated animals there is great variation in colouring, but not in the majority of wild species. What the causes are that operate in the painting of the skin of an animal no one can say, any more than one can say how particular spots are arranged on the petal of a flower or the wing of a butterfly. ”

“ These causes of coloration may be superposed and combined in a thousand ways. When birds are under the influence of physiological excitations like those of rage or love, the flow of blood contributes to enliven the color of the bare parts to the point of greatly modifying it. The bright, metallic tints of the peacock and the humming-bird are due to phenomena of interference and to the presence of a dark pigment combined; the green tint of the lizard to the association of a yellow pigment and blue-reflecting iridocytes. ”

“ Any competent observer of big game must be struck by the fact that in the great majority of the species the coloration is not concealing, and that in many it has a highly revealing quality. Moreover, if the spotted or striped young represent the ancestral coloration, and if, as seems probable, the spots and stripes have, on the whole, some slight concealing value, it is evident that in the life history of most of these large mammals, both among those that prey and those that are preyed on, concealing coloration has not been a survival factor ”

“ Warning Coloration and Mimicry
The colors of a great many animals, including a considerable percentage of American butterflies and their larvae, have been commonly explained by the theory of warning colors. According to this theory animals which [Pg 34] were for any reason not edible by birds and mammals have developed various striking combinations of color such as black and yellow, red and black, or black and white, in order to advertise to their foes their inedible qualities. ”

“ We took it for granted above that birds and mammals could discriminate between the red or yellow berry and the green foliage in whose midst it grows. Indeed, were other proof wanting, we should be justified in concluding that animals generally are possessed of a sense for the discrimination of color, from the mere fact that all those fruits and flowers which depend for their dispersion or fertilization upon animal agency are brightly tinted, while all those which depend upon the wind, or other insentient energies, are green or dull-brown in hue. ”

“ But in the eyes of all other creatures colour does make a marked difference in the impression which they convey to us, though the reason for this difference is obscure. Light-coloured eyes of any shade seem to detract strangely from the depth and significance of animal expression. The usual tint in these light-coloured eyes of animals is a bright golden yellow. ”

“ Bird enemies come from above rather than below, and it will be noticed that the modifications referred to all have reference to the upper plumage. Protective colouring, having for its object the preservation of the species which adopt it, will be found to enter more or less into the economy of every animal and bird and insect in a state of nature; and therefore it will be seen that there is a general harmony between the colours of an animal and those of its habitation, of which fact almost every living natural object furnishes evidence. ”

“ A thing still more astonishing is, that many animals in countries covered with snow become white in winter, and are said to change their colour again in the warmer months, as bears, hares, and partridges. Our domesticated animals lose their natural colours, and break into great variety, as horses, dogs, pigeons. The final cause of these colours is easily understood, as they serve some purposes of the animal, but the efficient cause would seem almost beyond conjecture. ”

“ Alluring coloration.—A few animals show what is called alluring coloration; that is, they display a color pattern so arranged as to resemble or mimic a flower or other lure, and thus entice to them other animals, their natural prey. Certain Brazilian fly-catching birds have a brilliantly colored crest which can be displayed in the shape of a flower-cup. The insects attracted by the false flower furnish the bird with food. ”

“ The puff-adder in this way forms a sort of horrid trap set in the woods which may be altogether unperceived till it shuts with a sudden spring upon its prey.
But that the main function of coloring is protection may be decided from the simplest observation of animal life in any part of the world. Even among the larger animals, which one might suppose independent of subterfuge and whose appearance anywhere but in their native haunts suggests a very opposite theory, the harmony of color with environment is always more or less striking. ”

“ Thus, for example, the action of light on the surface of the wings when in the resting posture may well inhibit the production of vivid pigment owing to some inherent physiological idiosyncrasy. But any individuals which lack this inhibiting factor—as some species which, though resting, are brightly coloured, appear to do—will be eliminated, if they live in an environment harbouring eliminating factors, which the exceptions to the rule we must suppose do not. But on this interpretation the fundamental factor in the determination of the coloration is the action of light. ”

“ Many very striking facts can be adduced in support of this theory, and no doubt it is of advantage to most species of mammals, birds, reptiles, and insects to harmonise in colour with their surroundings; but there are many instances in nature, especially amongst birds and insects, where a very striking and conspicuous coloration does not appear to have been prejudicial to the life of a species. ”

“ In the Mammals this pigment is always brown, and the varying tints of the hairs—black, brown, tawny, cream-colour or white—depends upon the amount of pigment and its disposition in the pith, combined with differences in the density of the envelope. In some cases, as about the mouth, eyes, and ears of the Cat, long sensitive hairs are connected with the terminations of nerves, which help the animal to feel its way. There are no marked colour differences in the fur of the sexes, such as we find in the plumage of Birds ”

“ Again, color in block or in variegation is not positive evidence of disease in animal life. The white Caucasian is as healthy as the negro, the copper-colored Malay as the red Indian. The horse, ox, and hog run through white and red to black both in solid and party-color, and all are equally healthy; so with the rabbit, dog, cat, and others of our domestic animals. In wild animals, birds, reptiles, fishes, and insects, it is the same, so that mere difference in color or combinations of color are not prima facie evidence of disease. ”

“ But if the colours of animals do really, in the various instances already adduced, serve for their concealment and preservation, then white or any other conspicuous colour must be hurtful, and must in most cases shorten an animal’s life. ”

“ It is, I believe, the general opinion of modern naturalists that, putting aside cases where brilliant colours may have been produced amongst birds and insects by the action of the law of sexual selection, the coloration of all living organisms is protective, "serving," as that distinguished naturalist Mr. Alfred Russel Wallace puts it, when discussing the [Pg 3] subject of the coloration of mammals, "to conceal herbivorous species from their enemies, and enabling carnivorous animals to approach their prey unperceived." ”

“ The examples now given lead us to the conclusion that colours acquired for the purpose of serving as a danger-signal to enemies are very widespread in nature, and, with the corresponding colours of the species which mimic them, furnish us with a rational explanation of a considerable portion of the coloration of animals which is outside the limits of those colours that have been acquired for either protection or recognition. ”

“ With the exception of blue, all colours are well represented; but the consideration of one or two facts seems to show that colour plays little part in their lives. Apart from the fact that to our eyes, at any rate, these gorgeous hues would be invisible in the depths, it is difficult to imagine that each of these gaily-coloured creatures can live amongst surroundings of its own hue. Again, it is characteristic that the colour is uniform. There is a marked absence of those stripes, bands, spots, or shading which play so large a part in the protective coloration of animals exposed to light. ”

“ It is well known that the color of most animals is adapted by Nature to the general tint of the country which they inhabit. Thus, having no contrast, the animal matches with surrounding objects, and is difficult to be distinguished. ”

“ Plumage color, like hair color, varies greatly among domesticated animals. This diversity is, no doubt, in part due to the striking nature of color variations, but chiefly to the fact that the requisite variations are afforded in abundance. The principal color varieties, in poultry as in other domesticated animals, are melanism, xanthism, and albinism. ”

“ Protective coloration, in some of its varied forms, has not improbably modified the appearance of one-half of the animals living on the globe. The white of arctic animals, the yellowish tints of the desert forms, the dusky hues of crepuscular and nocturnal species, the transparent or bluish tints of oceanic creatures, represent a vast host in themselves; but we have an equally numerous body whose tints are adapted to tropical foliage, to the bark of trees, or to the soil or dead leaves on or among which they habitually live. ”

“ The chief difficulties which remain, after accounting for protective coloration, are, first, the extraordinary differences between the tints and plumage of male and female in many birds; and, secondly, the conspicuous colours of certain creatures by which the attention of their enemies must necessarily be attracted. ”

“ When free, in health, and at ease, it is of a beautiful green; some parts excepted, where the skin being thicker and more rough, produces gradations of brown, red, or light grey. When the animal is provoked in open air, and well fed, it becomes a blue green, but when feeble, or deprived of free air, the prevailing tint is yellow green. Under other circumstances, and especially at the approach of one of its own species, no matter of which sex, or when surrounded and teased by a number of insects thrown upon him, he then almost in a moment takes alternately the three different tints of green. ”

“ It therefore seems possible that assimilative colouration may have been a first and a very general consequent in animal development; and that the subsequent protective resemblance acquired by numerous living creatures through the process of natural selection, when life had advanced to the competitive stage, is far too frequently used as an explanation for whole series of uniform phenomena in colouration, which have probably survived unaltered from remote antiquity. ”