A GAY DECEIVER
THE drongo cuckoo (Surniculus lugubris) is a bird of which I know practically nothing, I doubt whether I have ever seen it in the flesh. It is, of course, quite unnecessary to apologise for discoursing upon a subject of which one's knowledge is admittedly nil. In this superficial age the most successful writers are those most ignorant of their subject. When you know only one or two facts it is quite easy to parade them properly, to set them forth to best advantage. They are so few and far between that there is no danger of their jostling one another or be¬wildering the reader. Then, if you are conversant only with one side of a question, you are able to lay down the law so forcibly, and the public likes having the law laid down for it, it does not mind how crude, how absurd, how impossible one's sentiments are so long as one is cocksure of them and is not afraid to say so.
My lack of knowledge of the habits of the drongo cuckoo is, however, not my chief reason for desiring to write about it. I wish to discuss the bird because natural selectionists frequently cite it as bearing striking testimony to the truth of their theory, whereas it seems to me that it does just the opposite. Surniculus lugubris is, so far as I am able to judge, an uncompromising opponent of those zoologists who pin their faith to the all-sufficiency of natural selection to account for evolution in the organic world.
The drongo cuckoo is as like the king-crow as one pea is to another. This bird, says Blanford, " is remarkable for its extraordinary resemblance in structure and colourisation to a drongo or king-crow (Dicrurus). The plumage is almost entirely black, and the tail forked owing to the lateral rectrices being turned outwards." Blanford further declares that the bird, owing to its remarkable likeness to the king-crow, is apt to be overlooked.
This being so, it is quite unnecessary for me to describe the drongo cuckoo ; it is the image of a king-crow. But stay, perhaps there are some who do not know this last bird by sight. Such should make its acquaintance. They will find it sitting on the next telegraph wire they pass -: a sprightly black bird, much smaller than the crow (with which it has no connection), possessing a long, forked tail. Every now and again it makes little sallies into the air after the " circling gnat," or anything else insectivorous that presents itself. When you see such a bird you may safely bet on its being a king-crow; the off-chance of its proving a drongo cuckoo may be neglected by all but the ultra-cautious.
Not much is known of the habits of this cuckoo; but what we do know shows that, sometimes, at any rate, it makes the king-crow act as its nursemaid. Mr. Davison saw two king-crows feeding a young Surniculus. The consequence is that every book on natural history trots out our friend the drongo cuckoo as an example of mimicry. The mimicry is, of course, unconscious: it is said to be the result of the action of natural selection.
King-crows are, as every one knows, exceedingly pugnacious birds ; at the nesting season both cock and hen are little furies, who guard the nursery most carefully and will not allow a strange species to so much as perch in the tree in which it is placed.
It is thus obvious that the cuckoo who elects to victimise a king-crow is undertaking a "big thing," yet this is what Surniculus does. It accomplishes its aim by trickery; it becomes a gay deceiver, disguising itself like its dupe. Now I readily admit that the disguise may be of the utmost use to the Surniculus; I can well understand that natural selection will seize hold of the disguise when once it has been donned and possibly perfect it; but I cannot see how natural selection can have originated the disguise as such.
The drongo cuckoo may be called an ass in a lion's skin, or a lion in an ass's skin, whichever way one looks at things. When once the skin has been assumed natural selection may modify it so as better to fit the wearer; but more than this it cannot do.
I do not pretend to know the colour of the last common ancestor of all the cuckoos, but I do not believe that the colour was black. What, then, caused Surniculus lugubris to become black and assume a king-crowlike tail ?
A black feather or two, even if coupled with some lengthening of the tail, would in no way assist the cuckoo in placing its egg in the drongo's nest. Suppose an ass were to borrow the caudal appendage of the king of the forest, pin it on behind him, and then advance among his fellows with loud brays, would any donkey of average intelligence be misled by the feeble attempt at disguise ? I think not. Much less would a king-crow be deceived by a few black feathers in the plumage of a cuckoo.
I do not believe that natural selection has any direct connection with the nigritude of the drongo cuckoo. It is my opinion that, so far as the struggle for existence is concerned, it matters little to an animal what its colour be. Every creature has to be some colour: what that actual colour is must depend upon a great many factors ; among these we may name the metabolic changes that go on inside the animal, its hereditary tendencies, sexual selection, and natural selection. Is it natural selection that has caused the king-crow to be black ? I trow not.
The drongo is black because it is built that way; its tendency is to produce black feathers. Just as some men tend to put on flesh, so also some species of birds tend to grow black plumage. In the case of the king-crow sexual selection has possibly contributed to the bird's nigritude. It is possible that black is a colour that appeals to king-crow ladies. " So neat, you know ; a bird always looks well in black, and a forked tail gives him such an air of distinction."
As the hen drongo is a bird capable of looking after herself, even when incubating, there is no necessity for her to be protectively coloured. As I have repeatedly declared, one ounce of good solid pugnacity is a better weapon in the struggle for existence than many pounds of protective colouration.
Again, in the case of king-crows nigritude may be an expression of vigour, the outward and visible sign of strength.
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.