John F.L.S. Watson
Poachers and Poaching
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.
VII.
HOW THE WORLD IS FERTILISED
In approaching the subject of the geographical distribution of animals and plants, one is struck with the marvellous methods which nature adopts for the dispersal of her types. If the seeds of forest trees were merely shed to the ground immediately beneath, they would be in an environment precisely the least likely to further the reproduction of their kind. Instead of this, many of the seeds of forest trees are furnished with wings, an adaptation which allows them to be easily wafted by the wind, and thus fits them for wide dispersal. It is only by possessing some such advantage as this that certain species could survive at all. It is true that acorns and other kindred fruits do not possess this advantage, but then they are largely fed upon by birds, and birds, as will presently be shown, are an admirable means of dispersal. The crop of a wood-pigeon, which burst when the bird fell to the ground when shot, was found to contain sixty-seven acorns, besides a number of beech mast and leaves of clover. In this connection imagine the possible rate of multiplication which would follow the accidental dissemination of a single head of red poppy. If left undisturbed it would, under ordinarily favourable circumstances, ripen forty thousand seeds, each capable of producing a successor. It has been stated by a competent authority that one red poppy could produce plants enough in less than seven years to occupy every inch of the thirty and odd million acres of the United Kingdom.
Ocean currents have not unfrequently been the means of connecting the floras of different continents, and seeds and fruit are sometimes picked up on the western coasts of Britain which have been wafted across the whole Atlantic Ocean. It is also known that certain birds of long and sustained powers of flight cross the Atlantic unaided, and what this may possibly mean will presently be shown. Even land animals are known to cross straits between island and island upon rafts—drift-wood or bits of floating bark.
A quaint instance of transportation of fish spawn is given by an old writer. Izaak Walton believed that pike were bred from pickerel-weed; though he seems to have had some suspicion of this piece of unnatural history, and qualifies his statement by saying that if it is not so "they are brought into some ponds some such other ways as is past man's finding out." But one of his contemporaries attacks this heterodoxy, and "propounds a rational conjecture of the heron-shaw." He thinks it quite likely that while fishing the heron might "lap some spawn about her legs", in regard to adhering to the segs and bull-rushes near the shallows, as myself and others without curiosity, have observed. And this slimy substance adhering to her legs, and she mounting the air for another station, in all probability mounts with her. When note, the next pond she haply arrives at, possibly she may leave the spawn behind her, an observation now known to be strictly accurate. Herons are not the only birds which are aids to dispersal. Although the feet of birds are generally clean, Darwin in one case removed sixty-one grains, and in another twenty-two grains, of dry argillaceous earth from the foot of a partridge, and in the earth there was a pebble as large as the seed of a vetch. The same naturalist had sent to him by a friend the leg of a woodcock, with a little cake of dry earth attached to the shank, and weighing only nine grains; this contained seeds of the toad-rush, which not only germinated but flowered. But perhaps the most interesting case of all was that of a red-legged partridge forwarded by Professor Newton. This had been wounded, and was unable to fly; and a ball of hard earth adhered to it, weighing six and a half ounces. The earth had been kept for three years, but when broken and watered, and placed under a bell-glass, no fewer than eighty-two plants sprang from it.
American passenger pigeons are frequently captured in the State of New York with their crops still filled with the undigested grains of rice that, according to Mr. Howard Saunders, must have been taken in the distant fields of Georgia and South Carolina, apparently proving that the birds had passed over the intervening space within a few hours. It is known that at certain seasons thousands of these beautiful pigeons are killed, not only by man, but by predatory animals and birds; and their long migratory journeys as a possible means of dispersal becomes at once evident. As bearing on this particular subject, Darwin has proved that the hard seeds of fruit pass uninjured through even the digestive organs of a turkey. In the course of two months he picked up in his garden twelve kinds of seeds out of the excrement of small birds which seemed perfect, and some of them germinated. The crops of birds do not secrete gastric juice, and consequently do not in the least injure germination. Darwin forced many kinds of seeds into the stomachs of dead fish, and then gave them to fishing eagles, storks, and pelicans in the Zoological Gardens. The birds, after long intervals, either ejected the seeds in pellets or passed them; after which several kinds still retained the power of germination. In the tropics countless swarms of locusts sometimes suddenly make their appearance, and as suddenly vanish. They cover every leaf-bearing thing, and occasionally denude whole districts of their greenery. So great are their powers of flight that they have been seen at sea nearly four hundred miles from nearest land. In Natal the farmers, rightly or wrongly, believe that the locusts introduce injurious seeds upon their grass lands, and the following would seem to show that their belief is well founded. A Mr. Weale, who was in their way of thinking, collected a packet of dried pellets and sent them to England. When closely examined under the microscope they revealed a number of tiny seeds from which plants of seven kinds of grasses were ultimately raised.
In comparatively few years a small island in mid ocean had quite an important addition to its flora, merely from the fact that the grave of an officer was dug with a spade that had been used in England. The seeds from which these sprang were embedded in the dry earth adhering to the spade. Floating driftwood is quite an important means of dispersal, as can easily be understood; and the natives of some of the coral islands in the Pacific procure stones for their tools solely from the roots of drifted trees, the stones being a valuable royal tax. In this connection Darwin made the following interesting experiments. He found that when irregularly-shaped stones were embedded in the roots of trees, small parcels of earth were frequently enclosed in their interstices or behind them, so perfectly that not a particle could be washed away during the longest transport. Out of one small portion of earth thus completely enclosed by the roots of an oak about fifty years old three dicotyledonous plants germinated. It is well known that in many cases a few days' immersion in sea-water is sufficient to kill seeds, but a number taken out of the crop of a pigeon which had floated on the water for thirty days nearly all germinated. Other aids to dispersal already referred to are wading birds, which frequent the muddy edges of ponds, and, if suddenly flushed, would be the most likely to have muddy feet. "Birds of this order wander more than those of any other, and they are occasionally found on the most remote and barren islands of the open ocean; they would not be likely to alight on the surface of the sea, so that any dirt on their feet would not be washed off; and when gaining the land they would be sure to fly to their natural fresh-water haunts. I do not believe," says Darwin, "that botanists are aware how charged the mud of ponds is with seeds; I have tried several little experiments, but will here only give the most striking case. I took in February three tablespoonfuls of mud from three different points, beneath water, on the edge of a little pond; this mud when dried weighed only six and three-quarter ounces. I kept it covered up in my studio for six months, pulling up and counting each plant as it grew. The plants were of many kinds, and were altogether five hundred and thirty-seven in number; and yet the viscid mud was all contained in a breakfast cup. Considering these facts, I think it would be an inexplicable circumstance if water birds did not transport plants to unstocked ponds and streams, situate at very distant points. The same agency may have come into play with the eggs of some of the smaller fresh-water animals."
The manner in which the ubiquitous brown rat obtrudes itself everywhere is only paralleled by the like qualities in the British sparrow. Our weeds have migrated to the colonies, and certain kinds have almost overrun them. In New Zealand the common dock is now widely disseminated, the original seeds being sold by a lively British tar as those of the tobacco plant.
