African Nature Notes and Reminiscences

by Frederick Courteney Selous

The highly decorative but very conspicuously coloured plumage to be seen in the males of many species of birds, especially during the breeding season, was considered by the immortal Darwin to be due to the influence of sexual selection, and whatever may be urged against the correctness of this theory, it is supported by a long array of indisputable facts.

Great, however, as is the divergence between the plumage of the males and females in many species of birds, not only during the breeding season, but in a great number of cases at all times of year, and however gaudy and conspicuous the coloration of the former may be compared with that of the latter, such conspicuous coloration never appears to be prejudicial to the life of a species, though in some cases the brighter coloured male assists the female in incubation, and it would thus appear that in all such cases the sombre coloured plumage of the female was not absolutely necessary for purposes of protection against enemies.

I therefore think that if it is admitted that bright and conspicuous colours have been evolved in living organisms through the action of the law of sexual selection, without detriment to the life of the species in which such conspicuous colours are shown, it must be conceded that a coloration harmonising with its surroundings is not a necessity of existence in all cases to all species of mammals, birds, reptiles, and insects, and that it is therefore quite possible that where living organisms agree very closely in colour with their surroundings, such harmonious coloration may have been produced by some other agency than the need for protection by colour, and I would suggest that in addition to the influence exerted in the evolution of colour in living organisms by the action of sexual selection, and the necessity for protection against enemies, a third factor has also been at work, which I will call the influence of environment.

It is worthy of remark, I think, that in hot, dry deserts, where the climatic conditions are stable, and where the general colour of the landscape is therefore very much the same all the year round, all the resident species of mammals, birds, reptiles, and insects are what is called protectively coloured, that is to say, they are all of a dull brown or greyish coloration,[1] which harmonises beautifully with their parched, dull-coloured environment. In the leucoryx, the Saharan representative of the gemsbuck of South-Western Africa, all the black markings which are so conspicuous in the latter animal have disappeared or become pale brown, whilst the general colour of the body has been bleached to a dirty white. Now, no one can persuade me that if the leucoryx were coloured exactly like its near relative the gemsbuck, it would suffer one iota more, in the open country in which it lives, from the attacks of carnivorous animals than it does at present, and I therefore believe that the faded colour of the leucoryx, as compared with that of the gemsbuck or the beisa antelope, has not been brought about in order to serve as a protection against enemies, but is directly due to the influence of its desert environment, and constant exposure to strong sunlight on treeless plains. Again, from the point of view of a carnivorous animal hunting for food by daylight and by sight, no two countries could be more alike than the open karoos of the Cape Colony and the plains in the neighbourhood of Lakes Nakuru and Elmenteita in British East Africa, where the grass is always kept very short by the large herds of game, as well as by the cattle, sheep, and goats belonging to the Masai, which pasture there. Before the advent of Europeans, the carnivorous animals inhabiting the Cape Colony were exactly the same as those found to-day in East Africa, viz. lions, leopards, chetahs, wild dogs, and hyænas. In both districts lions were once numerous, and in both zebras formed the principal food of these carnivora. But whereas Equus granti, the form of zebra found on the plains near Lake Nakuru, is the most brilliantly coloured representative of the genus to which it belongs, with jet black stripes on a pure white ground, the now extinct form of zebra—Equus quagga—which once abounded on the plains of the Cape Colony, was of a dull grey brown in ground colour, with darker brown stripes on the head, neck, and fore-part of the body alone. Now, these two races of zebras, both living on bare, open plains, could not both have been coloured in the best possible way to escape being seen by the lions which constantly preyed upon them. If, as has been contended, the juxtaposition of the black and white stripes in Grant's zebras renders these animals not only inconspicuous, but almost invisible under strong sunlight on an open plain, and is, in fact, the supreme triumph of protective coloration in large mammals, why had the quaggas of the Cape Colony become dull brown, for they also lived on open plains in strong sunlight, and needed protection from the lions every bit as much as their congeners of East Africa? Moreover, I think all naturalists and embryologists are agreed that Equus quagga was the descendant of boldly striped ancestors.

[1] The cock ostrich is, I think, the only exception to this rule, and in the case of this remarkable bird the influence of sexual selection has probably been more potent than that of a dull-coloured, monotonous environment.

To my mind the loss of stripes in the quagga was entirely due to the environment in which this species had lived for long ages; for on the karoos of the Cape Colony everything is of one dull brown colour, whether on hill or plain, and no shade is to be found anywhere, for the whole country is without trees. The air, too, is intensely hot and dry, and the rainfall scanty. In these semi-deserts of South-Western Africa, not only did the quaggas lose their black stripes, but the elands also lost the white stripes of their immediate ancestors, whilst the blesboks had already lost much of the white to be seen in the body colouring of the bonteboks, from which they are descended, and had become of a much duller colour generally. In East Africa, however, the plains are surrounded by well-wooded hills, which give some colour to the landscape, whilst the rainfall every year is heavy. If it is not the influence of their several environments which has brought about the differences between the well-striped elands and zebras of East Africa and their dull-coloured relatives that once lived in the karoos of the Cape Colony, the theory of protective coloration must be equally at fault, for in spite of the fact that in both countries both races of these animals have been hunted by lions from time immemorial on open plains, and under precisely similar conditions, they developed very different schemes of coloration.

The Barbary sheep, again, which inhabits the dry hills bordering the deserts of Northern Africa, where the vegetation is parched and scanty at all seasons of the year, and the rocks of a red brown colour, is itself of a uniform reddish brown which harmonises exactly with its surroundings, and makes it very difficult to detect when lying at rest amongst rocks. This perfect harmony of coloration with its surroundings in the Barbary sheep may have been brought about by the need of protection from enemies, but seems to me far more likely to have been caused by the influence of the colour of its environment, for its four-footed foes hunt by scent and by night far more than by sight during the daytime.

The male moufflon of Sardinia, which lives in a temperate climate where the colours of its surroundings are much brighter and more diversified than is the case in the habitat of the Barbary sheep, is a much more conspicuously coloured animal than the latter, or than the females of its own kind. As the females and young of the Sardinian moufflon, which are of a uniform brown colour, are more difficult to see than the males in their somewhat conspicuous autumn and winter coats, the latter cannot be said to be protectively coloured. Either through the influence of sexual selection or that of an environment the general colour of which varies very greatly at different seasons of the year, the male of the Sardinian moufflon becomes during autumn and winter conspicuously coloured compared with the female, without detriment, however, to the well-being of the species.

During my long sojourn in the interior of South Africa, I made large collections of butterflies. There was one species (Precis artaxia, Hewits) which always puzzled me. This handsome insect is only found in shady forests, is seldom seen flying until disturbed, and always sits on the ground amongst dead leaves. Though handsomely coloured on the upper side, when its wings are closed it closely resembles a dead leaf. It has a little tail on the lower wing which looks exactly like the stalk of a leaf, and from this tail a dark brown line runs through both wings (which on the under sides are light brown) to the apex of the upper wing. One would naturally be inclined to look upon this wonderful resemblance to a dead leaf in a butterfly sitting with closed wings on the ground amongst real dead leaves as a remarkable instance of protective form and coloration. And of course it may be that this is the correct explanation. But what enemy is this butterfly protected against? Upon hundreds of different occasions I have ridden and walked through the forests where Precis artaxia was numerous, and I have caught and preserved many specimens of these butterflies, but never once did I see a bird attempting to catch one of them. Indeed, birds of all kinds were scarce in the forests where these insects were to be found. I now think that the form and colour of the under wings of Precis artaxia have more probably been produced by the influence of its environment than by the need for protection.

During the rainy season in South Africa, the open glades in the forests bordering the rivers are gay with multitudes of brightly coloured butterflies of many different species, and after a night's rain butterflies of various kinds may often be seen settling in masses round pools of water along waggon roads. Most of these butterflies are conspicuously coloured, though they are in perfect harmony with the sunlit flowers which spring up at the time of year when they appear. I cannot, however, believe that the need for protection against birds or other enemies has had anything whatever to do with the determination of their various colours, as in all my experience (and I have been all my life a close observer of nature) I have never once seen a bird feeding upon butterflies in Africa.