Poachers and Poaching

by F.L.S. John Watson

VI.
ADAPTATION TO HAUNT.

The process of natural selection, tending to the survival of the fittest, would almost invariably seem to use colour as its main working factor. The exemplification of this law is, perhaps, nowhere better seen than in the colouring of animals and birds. In the keen struggle for existence, the creature which conforms most nearly to its environment is the one most likely to survive, and therefore perpetuate its characteristics. For upon the fact that the peculiarities of the parents are reproduced in their offspring depends the whole theory of evolution. This may at first suggest that the generality of animals and birds closely conform to the type of the parent stock, and that therefore there is little chance of variation. But while this is so, it is equally true that when any "sport" occurs this is tenaciously retained providing it possesses any advantages over its neighbours in the struggle for existence. In this way a new type may be set up, differing so far from the original as in time to rank as a species.

The great power of variability in animals and plants is probably not yet fully comprehended. We know, however, from Darwin's experiments how many distinct varieties in the case of pigeons have been produced from the wild blue rock, each showing profound modification, not in colour alone, but also in bone structure. Then there are those which show the development of hoods and frills, and others, again, which have within them the homing instinct to an almost incredible degree. All this, of course, has been brought about by man, mostly by selection, and it serves to show how pliable nature is. What has been done to pigeons applies to domestic animals. Given a few years, any monstrosity can be produced, however extravagant; our shorthorns and blood horses have been produced out of the very sorriest material, and now stand as the idealised types of their kind. And what man does artificially, nature is doing daily, but by slow and sure methods of her own. None but those who have dipped beneath the surface can conceive of the struggle which is going on for existence. Nature's competition is of the keenest kind; the strongest survive, the weakest go to the wall. Even an object so low in the scale of animal creation as a chrysalis assumes a red coat when it is attached to a bright brick wall, and a grey one when it affixes itself to limestone. This inherent power it has in itself, and those individuals which can most cleverly practise deceit in hiding from birds and other enemies survive and reproduce their kind.

With regard to instances of variability which come under our immediate notice, the red grouse of our moorlands as already mentioned is a striking example. There can now be no doubt that this is the "willow grouse" of the Scandinavian Peninsula. Our indigenous bird found itself in an insular position, and has changed from white to speckled red so as to conform to the colour of the heather; it has also modified the colour of its eggs to suit the changed conditions of its existence. Had it remained white, it would soon have been wiped out of existence by the peregrine and other of the large falcons. There can be no question that bird and animal or insect dons the colour and form best calculated to protect it. Whether this change is conscious to the creature that practises it is beside the main question, and hardly enters into the issue. The process is invariably slow, but if any "accidental sport" occurs which is likely to be of use, it is tenaciously retained, and progress is made at a bound.

Many of our British birds exhibit capital instances of protective colouring, and it is a somewhat striking fact that birds of sombre plumage build open nests, while the brilliantly coloured birds either have covered nests or build in holes in trees.

Returning to sexual colour, the dull summer female plumage which characterises so many ground-feeding birds is all the more remarkable as they are the mates of males for the most part distinguished by unusual brilliancy of plumage. The few exceptions to this rule are of the most interesting nature, and go eminently to prove it. In these exceptions it happens that the female birds are more brightly plumaged than the males. But the remarkable trait comes out that in nearly the whole of these cases the male sits upon the eggs. Now this fact more than any other would seem to indicate that the protection afforded by obscure colouring is directly intended to secure the bird's safety during the long and most critical period of its life. This law of protective colouring, it will be seen, most influences those species which build on the ground, and one or two examples may be adduced from our own avi-fauna, as in the case of the rare dotterel, which breeds on the fells. In winter the colouring of the sexes in this species is almost identical; but when the breeding season comes round, the female dons a well-defined and comparatively conspicuous plumage, while it is found that the dull-coloured male alone sits upon the eggs.

Mr. Wallace has pointed that the bee-eaters, mot-mots, and toucans—among the most brilliant of tropical or semi-tropical birds—all build in holes in trees. In each of these cases there is hardly any difference in the plumage of the sexes, and where this is so the above rule is almost invariable. Again, our native kingfisher affords an illustration. Woodpeckers, many of which are brightly coloured above, build in the boles of trees, and our own titmice, with their exquisite tints, construct domed nests. Visitors to the Zoological Gardens in Regent's Park will have noticed that the orange-plumaged orioles have pensile nests, which is a characteristic of the order to which they belong, most of the members of which are conspicuous. 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.

There comes periodically to this country a bird of the starling kind, known as the rose-coloured pastor. It has the back, breast, and sides of an exquisite pale pink; and it is perhaps this bright plumage which prevents it from establishing a residence here. In its continental haunts the bird is observed to affect trees or shrubs bearing rose-coloured flowers, such as the blossoms of the pink azalea, among which the birds more easily escape notice. This is an instance of what is known as adaptive or protective coloration, which we need not go abroad to observe.

The struggle for existence among plants and animals is a hard one, and every point gained in the direction tends to survival. The modification in the forms and colours of insects, and the successful shifts thereby made to elude their enemies, provide the striking facts of the case. Birds modify and rearrange the colours of their plumage, adapt the coloration of their eggs, and the structure and material of their nests, all to the same end. We know that the more highly organised flowers have changed form and colour to satisfy their insect visitors, while the insects themselves have modified their organs so as to enable them the better to visit certain flowers. In Sumatra Mr. Wallace found a large butterfly, its upper surface of a rich purple and with a broad bar of deep orange crossing each wing. The species is found in dry woods and thickets, and when on the wing is very conspicuous. Among the bush and dry leaves the naturalist was never able to capture a specimen; for, however carefully he crept to the spot where the insect had settled, he could never discover it until it suddenly started out again. But upon one occasion he was fortunate enough to note the exact spot where the butterfly settled, and, although it was lost sight of for some time, he at length discovered it close before his eyes. In its position of repose it exactly resembled a dead leaf attached to a twig.

So in our own country we may observe that the purple emperor butterfly affects certain of the brightly coloured wild geraniums, upon which, in repose it is almost impossible to detect it. The brown-spotted fritillaries of our birch woods also offer examples of this class, it being difficult to detect them against the fungus-pitted leaves of every shade of brown and dun and yellow.