All the time he is thus bowing or bobbing the turtle-dove utters a deep, rolling, musical note which is continuous (or sounds so), and does not cease till he has got back into his more everyday attitude. The hen looks sometimes surprised, sometimes as though she had expected it, and sometimes, I think,—but of this I am not quite positive—she will return the little series of musical bobs. This is in tree-land; but I have seen the turtle-dove court on the ground, and he then, between his bobbings, made a curious dancing step towards the female, who retired and gave her final answer by flying away. But, besides this, these birds have another and most charming nuptial disportment. Sitting à deux in some high tree, one of them will every now and again fly out of it, mount upwards, make one or two circling sweeps around and above it, then, after remaining poised for some seconds, descend on spread wings in the most graceful manner, alighting on the same branch beside the waiting partner. This is a beautiful thing to see, and especially in the early fresh morning of a clear, lovely day. It seems then as if the bird kept flying up to greet "the early rising sun," or as rejoicing in the beauty of all things. These are the coquetries, the prettinesses of loving couples, as to which—on one side at least—what has not been said by the writers of our clumsy race! But "if the lions were sculptors"—How might a bird novelist expatiate!
Turtle-Doves: The Nuptial Flight.
Not less beautiful is the nuptial flight of the wood-pigeon. Of this, the clapping of the wings above the back is the most salient feature, a sound which is never heard during the winter or after the breeding-season is fairly over. In full flight, the bird smites its wings two or three times smartly together above the back, then, holding them extended and motionless, it seems to pause for one instant—if there can be pause in swiftest motion—before sinking and then rising and sinking again, as does a wave, or as though it rested on an aerial switchback. Then continuing his flight—recommencing, that is to say, the strokes of his wings—he may do the same when he has gone a few air-fields farther, and so "pass in music out of sight." Sometimes there will be only a single clap of the wings instead of two or three,[5] but always it is made just before the still-spreading of them, and the hanging pause in the air; for let the speed be never so great—and it hardly seems possible that it could be checked so suddenly, and why should the bird wish to check it?—yet the effect upon the eye of the wings extended and motionless after they have been pulsating so rapidly is as of a pause. This pause, or rather this rest-in-speed, as the bird, renouncing all effort, is carried swiftly and placidly onwards in a curve of the extremest beauty has a delicious effect upon one. One's spirit goes out until one seems to be with the bird oneself, hanging and sweeping as it does. Yet in this glory of motion it will often be shot by beings, in all grace and beauty and poetry of life, how infinitely its inferiors! This makes me think of Darwin's comment upon Bate's account of a humming-bird caught and killed by a huge Brazilian spider, wherein the destroyer and the victim—"one, perhaps, the loveliest, the other the most hideous in the scale of creation"[6]—are contrasted. Spiders, too, had they their Phidiases, might be idealised and made to look quite beautiful in marble, even perhaps to our eyes (what cannot genius do?) whilst to their own, of course, the spider form would be "the spider form divine."
[5] Sometimes, too, not any, the flight being the same.
[6] I quote from memory.
Wood-pigeons will also fly circling about above the trees in which they have been sitting, in rapid pursuit of each other, and whilst doing so, one or other of them may be heard to make a very pronounced swishing or beating sound with the wings, reminding one of the peewit, nightjar, and a great many other birds. Of instrumental music produced during flight, the snipe is a familiar example. Here, however, the very peculiar and highly specialised sound known as bleating or drumming is produced, not by the feathers of the wing, but by those of the tail, which have been specially modified, as we may suppose (those, at least, of us who are believers in that force), by a process of musical sexual selection. To quote Darwin: "No one was able to explain the cause until Mr Meves observed that on each side of the tail the outer feathers are peculiarly formed, having a stiff sabre-shaped shaft with the oblique barbs of unusual length, the outer webs being strongly bound together. He found that by blowing on these feathers, or by fastening them to a long thin stick and waving them rapidly through the air, he could reproduce the drumming noise made by the living bird. Both sexes are furnished with these feathers, but they are generally larger in the male than in the female, and emit a deeper note."
The possibility of reproducing the sound in the manner described seems conclusive as to the cause of it. Otherwise I should have come to the conclusion, by watching the bird, that the wings and not the tail were the agency employed.
"I have just been watching for some time a snipe continually coursing through the air and making, at intervals, the well-known drumming or bleating sound,—bleating certainly seems to me the word which best expresses its quality. The wings are constantly and quickly quivered, not only when the bird rises or flies straight forward, but also during its swift oblique descents, when one might expect that they would be held rigid in the ordinary manner. From each sweep down the bird rises and beats again upwards, but when the flight has been continued long enough the wings are pressed to the sides as the plunge to earth is made, which is also one way in which the lark descends. It is during these downward flights—but not during the descent to earth—that the sound strikes the ear. A second bird flies, to my surprise and interest, quite differently. After scudding about for some little time in a devious side-to-side pathway, less up and down, as it seems to me, than the other, it suddenly tilts itself sideways, or almost sideways—one wing pointing skywards, the other earthwards—and makes a rapid swoop down, with the wings not beating. I watch it doing this time after time, both with the naked eye and through the glasses, and each time that the swoop is made no bleating or other sound accompanies it: the flight is noiseless, like that of an ordinary bird. Two other snipes are now flying about in this latter way and chasing each other. At first—and this included a great many sweeps down—I heard no sound. Afterwards I thought I heard it faintly sometimes, but could not be sure that it was not made by another bird—a frequent difficulty in watching snipe." Again, "A snipe is standing alone 'in the melancholy marshes,' quite still, and uttering the creaky, see-sawey note. I can see the two long mandibles of the beak dividing slightly and again closing. The note is now thin and subdued, but, the bird taking flight suddenly, it becomes much accentuated. It joins two other birds in the air, and all three now sport and pursue each other about, constantly uttering this cry, but bleating only occasionally. I am lying flat on the ground, and they often fly close about and over me, the light, too, being good, it being all before 5.40, and not much after 5, perhaps, when it commenced (this was April 4th). I note that they often descend through the air without vibrating the wings, and there is then no bleating sound—this whilst quite close. I think—but am not yet quite sure—that they sometimes descend in this way uttering the cry. When they bleat, however, there is never the cry at the same time. It is impossible to tell when these birds are going to alight, as they often descend in the manner that they use when alighting, but, when almost down, skim a little just over the ground, and, rising again, continue their flight as before. Yet that they have had it in their mind to alight I feel sure, for they always do so with that particular action."
Since, then, the snipe has two ways of making his rapid descents through the air, in one of which he quivers his wings and in the other not, and since, on the latter occasion, the bleat is not heard or, if heard, only faintly, it would be natural to suppose that the sound—if not vocal—was produced by the rapidly vibrating feathers of the wing when in swift downward motion rather than by those of the tail, which should not, one would think, be affected by the difference. Also the fact of the vocal note not being uttered at the same time as the bleat might make one think that this, too, was vocal. Such arguments, however, would be at best but "poor seemings and thin likelihoods"—the last one, I believe, not supported by what we know (at least I cannot at the moment think of a bird that produces vocal and instrumental music at the same time). If the sound can really be reproduced by waving the modified feathers of the tail, then this is a demonstration.[7]