Let me make myself clear. Suppose that in a race of savages those that had fair hair were stronger, bolder, more prolific, and more pushing than the dark-haired men. Fair hair, in some inexplicable way, always accompanied strength and the like. It is obvious that, under these conditions, the race would in time become fair-haired: the milder dark men would eventually be hustled out of existence. Fair hair would then be the outward expression of vigour: it would not be the cause of vigour, merely the accompaniment of it; nor would it be a direct product of natural selection. In the same way it is possible that among drongos nigritude is in some manner correlated with vigour. This idea is not altogether fanciful. Are there not horses of “bad colour”? Are not white “socks” a sign of weakness? Is not roan a colour indicative of strength and endurance in a horse?
May not the blackness and the forked tail of the drongo cuckoo have arisen in the same way as they arose in the king-crow? In each case it may be an accompaniment of vigour, or it may be the result of sexual selection. Mrs. Surniculus may have had similar tastes to Mrs. Dicrurus, and, since cuckoos seem to be very plastic birds, her tastes have been gratified. As another example of this plasticity I may cite Centropus phasianus—a cuckoo which is a very fair imitation of a pheasant.
On this view the resemblance is a mere chance one. The cuckoo is not an ass in a lion’s skin, but an ass that looks very like a lion. His lion-like shape was not forced upon him by natural selection. A variety of causes probably contributed to it. It was not until the resemblance had arisen and become very striking that it was directly affected by natural selection.
I am far from saying that the above is a correct explanation of the nigritude: it is all pure hypothesis. Even if it be correct, we are really very little further than we were before towards an explanation of the colours and shape of either the king-crow or the drongo cuckoo.
Why did these birds tend to grow black feathers rather than red, green, or blue ones?
This is a question which “stumps” us all.
THE EMERALD MEROPS
If I have a favourite bird it is the little green bee-eater (Merops viridis). There is no winged thing more beautiful or more alluring. More showy birds exist, more striking, more gorgeous, more magnificent creatures. With such the bee-eater does not compete. Its beauty is of another order. It is that of the moon rather than of the sun, of the violet rather than of the rose. The exquisite shades of its plumage cannot be fully appreciated unless minutely inspected. Every feather is a triumph of colouring. No description can do the bird justice. To say that its general hue is the fresh, soft green of grass in England after an April shower, that the head is covered with burnished gold, that the tail is tinted with olive, that a black collarette adorns the breast, that the bill is black, that a streak of that colour runs from the base of the beak, backwards, through the eye, which is fiery red, that the feathers below this streak are of the purest turquoise-blue, as are the feathers of the throat—to say all this is to convey no idea of the hundred shades of these colours, or the manner in which they harmonise and pass one into another. Nor is it easy for words to do justice to the shape of the bird; even a photograph fails to express the elegance of its carriage and the perfection of its proportions. Were I to string together all the superlatives that I know, I should scarcely convey an adequate impression of the grace of its movements. I can but try to make the bird recognisable, so that the reader may see its beauties for himself.
He should look out for a little green bird with a black beak, slender and curved, and a tail of which the two middle feathers are very attenuated and project a couple of inches as two black bristles beyond the other caudal feathers. The bird should be looked for on a telegraph wire or the bare branch of a tree, for the habits of bee-eaters are those of fly-catchers. The larger species prey upon bees, hence the popular name, but I doubt whether the little Merops viridis tackles an insect so large as a bee. It feeds upon smaller flying things, which it captures on the wing. As it rests on its perch its bright eyes are always on the look out for passing insects. When one comes into view, the bird sallies forth. Very beautiful is it as it sails on outstretched wings. The under surface of these is reddish bronze, so that their possessor seems to become alternately green and gold as the sun’s rays fall on the upper or lower surface of its pinions. Its long mandibles close upon its prey with a snap sufficiently loud to be audible from a distance of five or six yards. This one may frequently hear, for bee-eaters are not shy birds. They will permit a human being to approach quite near to them, as though they knew that the fulness of their beauty was apparent only on close inspection.
The little green bee-eater utters what Jerdon calls “a rather pleasant rolling whistling note,” which, if it cannot be dignified by the name of song, adds considerably to the general attractiveness of the bird. Bee-eaters are, alas! not very abundant in Madras, but, if looked for, may be seen on most days in winter. The Adyar Club grounds seem to be their favourite resort. When driving into the club at sunset I have often surprised a little company of them taking a dust bath in the middle of the road. The bath over, the little creatures take to their wings and enjoy a final flight before retiring for the night.