THE NATURALIST.

Otago Witness, Issue 1934, 19 March 1891, Page 30

THE NATURALIST.

PROTECTIVE COLOURING Iff BIRDS. There comes periodically to the British Isles 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 it is observed to affect trees or shrubs bearing rosecoloured flowers, such as the blossoms of the, jink azalea, among which the birds easily escape notice. This is an instance of what is known as adaptive or protective colouration, but we need not go' abroad to observe,. The struggle for existence among plants and aoimals is a hard one, and every point gained in the direction indicated tend,s to survival. The modification in the form and" colour of insects', and the successful shifts thereby made tbelude^ theirenemies, provide the striking facts of the case. "B.irds modify and rearrange the colours "of their plumage, adapt the colouration 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 both form and colour to satisfy 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, 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 bush and dry leaves the naturalist was never able to capture, a specimen, for, however carefully he orept to the spot where the

insect had settled, he could never discover ifc until the insect suddenly started out again. But on 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 resembles a dead leaf attached to a twig. So in Great Britain 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 f titularies of our birchwoods 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. Birds afford the most numerous examples. The pencilled plumage of the snipe lying still in the brown marshes is almost impossible to detect, although the birds get up at one's feet everywhere. The same may be said of the woodcock in the leaf-strewn woods, and of the nests and eggs of both species. The egga of the wild duck assimilate to the colour of the pale green reeds, and those of the lapwing to the ploughed fields or the upland. During the breeding time of the common green plover, a person unaccustomed to bird nesting was sent up a furrow in which there were six nests, each containing eggs which were to be collected. By the time the end of the furrow was reached the collector had put his foot into one nest and failed to find the other five. The colour of red grouse conforms very nearly to that of the brown and purple heather among which they lie, as do also their richly- speckled eggs. The part- , ridge has a double protection. It is most difficult to pick out her quiet brown plumage from ithe hedge bottom so long as she remains still. She adopts the duns and browns of the dead leaves among which ehe lies. When she leaves her eggs deliberately she is careful to cover them over ; but this seems almost superfluous, for there is no great contrast between the tint of the eggs, and that of the leaves among which they lie. A hen pheasant sitting in a bracken bed- is equally difficult to detect ; and this • applies particularly to the young of all the game birds just mentioned. Tha bright dark eyes of birds and animals frequently betray their presence, those of the former being generally large and prominent. A shorteared owl on a peat moss we have mistaken for a clod of turf ; and a gaunt heron with wind-fluttered feathers for drift stuff caught in the swaying branches of the stream. Another characteristic case of "protective imitation and colouring is furnished by the nightjar or goatsucker. This large nightflying bird, half owl, half swallow, rests during the greater part of the d&y on bits of bare limestone of the fells. Its mottled grey plumage exactly corresponds with the grey of the stones ; and its eggs, in colour like its plumage, are laid upon the bare ground Without the slightest vestige of a nest, and pgain entirely resemble the stone. It will be remarked that all these birds live much upon the ground, obtaining the principal part of their food therefrom, and therefore have special need of protection. And then incubation in 'every case takes place on the ground ; and just as the' imitation of the female bird is perfect, so will the fact tell upon the survival of the', species. There is no such need for tree builders, as these for the most part are out of the reach of predatory animals. The chaffinch is by far the most abundant bird of our fields and woods ; and there is one good reason why it should be so. It invariably covers its nest on the outside with dead lichens like those of the trunk against which its nest is bnilt. Against predatory boys and birds and animals the device succeeds admirably, with the result that the chaffinch as a species flourishes vigorously. The common wren constructs her nest of moss, and places j^t-upon a mossy background, so as to present no ' sharp contrasts. Sometimes she interweaves one or two dead oak leaves, so as to render the deception ' more deceitful ; and from the number of wrens which abound, she evidently succeeds. < Starlings and sparrows and jackdaws, which build in holes of a considerable elevation, | and have therefore less need of protection, hang out straws and sticks and bits of wool and feather as impudent advertisemepts. But wheatears and such birds as build in low walls cannot afford to do this; they build neat nests, leaving no trace without. Several of our warblers" drag dead leaves to the outside 6f their nests, and a hundred others employ like ingenuities. Fish rapidly assimilate to the colour of the river-bed; and the same rule applies to animals. It is commonly known that mountain hares are brown in summer, white in winter; so are ermines, silver f6xes, ptarmigan', snow buntings, the snowy owl, Iceland falcons, and a host of other creatures. All assimilate to the general colour of the ! ground on which they, live ; and the one which assimilates most. closely is the most successful as a species.— Chambers' Journal.

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