African Nature Notes and Reminiscences

by Frederick Courteney Selous

CHAPTER I

NOTES ON THE QUESTIONS OF PROTECTIVE COLORATION, RECOGNITION MARKS, AND THE INFLUENCE OF ENVIRONMENT ON LIVING ORGANISMS

Harmony of colour in nature—Theory of protective coloration—Sexual selection—Conspicuous colours not harmful—The influence of environment—The leucoryx—The Barbary sheep—The Sardinian moufflon—African butterflies—Coloration of the musk ox and caribou—Arctic hares and foxes—Coloration of mammals in the Yukon Territory—The chamois in winter—Examples of conspicuous coloration in African mammals—Colour not always protective—Carnivorous animals usually hunt by scent—Wild dogs and wolves—Wild dog and sable antelope—Sense of smell in herbivorous animals—Sight of antelopes—Experience with waterbuck—Dull sight of caribou—Demeanour of wild animals when alarmed—Small antelopes—Lions—Large antelopes—Difficulty of seeing wild animals sometimes exaggerated—Powers of sight of Bushmen—Colour not protective against animals which hunt by night and by scent—Animals in motion easy to see—Restlessness of wild animals—Lions attacking bullocks—Zebras the principal prey of lions since the disappearance of buffaloes—Appearance of zebras—Undoubtedly conspicuous animals in open country—Zebras by moonlight—Strong smell of zebras—Conspicuous antelopes in East Africa—Effect of the juxtaposition of black and white—Bold coloration of the sable antelope.

Although there are certain striking exceptions to the general rule, yet, broadly speaking, it cannot be gainsaid that living organisms are usually coloured in such a way as to make them difficult of detection by the human eye amongst their natural surroundings. Every collecting entomologist knows how closely certain species of butterflies when resting with closed wings in shady forests resemble dead leaves, or moths the bark of trees. Birds too, especially those which nest on the ground, often harmonise with their surroundings in a most marvellous way.

In the open treeless regions within the Arctic Circle, as well as on bare mountain ranges, nearly all the resident species of animals and birds turn white in winter, when their whole visible world is covered with an unbroken mantle of pure white snow, and become brown or grey during the short period of summer.

In treeless deserts again within the tropics, where the rainfall is very scanty and the climate excessively hot and dry, with intense sunlight throughout the year, all resident living organisms, mammals, birds, reptiles, and insects, are found to be of a dull coloration which harmonises in the most wonderful way with the sandy or stony soil on which they live. It is also very often the case that animals which live in forests where the foliage is not too dense to allow the sun to penetrate are spotted or striped, whilst those which live in really thick jungle or amongst deep gloomy ravines are of a uniform dark coloration.

Now a most interesting question arises as to the true causes which have brought about the extraordinary variations of colour to be seen in living organisms inhabiting different parts of the world.

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 subject of the coloration of mammals, "to conceal herbivorous species from their enemies, and enabling carnivorous animals to approach their prey unperceived."

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.