The Bird Watcher in the Shetlands/Chapter 17
CHAPTER XVII
MOUTHS WITH MEANINGS
THE young kittiwake differs in appearance from the parent birds in a quite uncommon manner, for, being prettily and saliently marked, it looks like a mature gull of another species, whereas the young of other gulls, being plain brown things, suggest their juvenility on the analogy of pheasants or birds of paradise. The general colour is mauvy grey, but black, falling here and there upon it, seems striving to blot it out. Half of the wings are thus darkened, and a broad half-moon of sooty black nearly encircles the neck, looking like black velvet on the back of it, where it is by much the broadest. There is a clouded black mark, too, on either side of the head, with some nuances of black between, black tips the tail, and the beak is all black. The tout ensemble of all this is very pretty, and the young kittiwake is a pretty bird. Mauve and black velvet is the dress it comes out in, and it looks like a soft little dove. Many might admire it beyond the grown bird, but, personally, I prefer the latter.
One of these well-grown young kittiwakes has just been fed by the mother, or father—but call it the mother, it always sounds better. Being importuned by sundry little peckings at her beak, she opened it, and the young one, thrusting in its own, helped himself as though her throat were a platter. It was much the same as with the fulmar petrels. Numbers of the young have left their nests, and keep all together, standing on the rocks or floating on the sea. Others remain, and I notice that these keep flapping their wings. This must strengthen them, and have the effect of preparing Dædalus for his first flight—for it seems probable that these particular ones have not made it. But they have, though, and bang goes a provisional hypothesis! Every moment, to laugh at me, one or other of them is flying out from the ledges, whilst others are returning to them.
When one of these young kittiwakes opens its bill, it is at once apparent that the inside of its mouth is much less brilliantly coloured than it is in the parent bird, being of a pale pinkish, merely, with, perhaps, a tinge of light yellow. As for the grown bird's mouth, one can hardly exaggerate the lurid brightness of it. The whole buccal cavity, including, as I think is usual, the tongue, is of a fine rich red, or orange-red colour, carrying on that of the naked skin adjoining the mandibles outside, with which, indeed, it is continuous. It is just the same in the case of the old and young shag. The mouth of the former presents a uniform surface of splendid gamboge, whilst that of the latter is almost the natural pink, only just beginning to pass into yellow. In the young guillemot, also, the interior of the mouth is pinkish merely, whilst in the grown bird it is of a pleasing lemon or gamboge. With the fulmar petrel again, we have much the same thing, though here—and this is significant—the difference, as well as the actual colour, is less striking. These varying degrees of brilliancy of colouring in this particular region, as between the mature and immature form, must surely have some meaning, and as it goes hand-in-hand with a similar, if not, as I believe, an identical difference in the hue of the naked facial integument, as well as with the pattern and shade of the plumage, I feel persuaded that all three are governed by the same general law.
As explained by Darwin—and nothing better, that I can see, than opposition has ever been opposed to his views—the beauty of certain birds has been acquired through the principle of sexual selection, and the lesser degree of it, which we notice in the young, represents the earlier and less-finished beauty of the adult in times gone by. Of all the elements which go to make up the beauty thus acquired, colour, on the whole, plays the most conspicuous part, and nothing can be more brilliant and striking than some of the colours that I am here speaking of. The only reason, therefore, why, in their use, and the laws that have governed their acquirement, they should be thought to differ from the hues and tintings of the plumage, or of the naked outer skin—the cere or the labial region—would be their habitual, necessary concealment. If, then, it can be shown that, far from their being always concealed, they are prominently displayed during the breeding season by certain birds which possess them in a marked degree, then, as far as these birds are concerned, there ceases to be a reason for thus, in idea, separating them. Let us see, now, how far this is the case. To begin with these kittiwakes, in their courting, or rather connubial actions on the ledges—as may be seen now, but much more earlier in the year—both sexes open their bills widely, and crane about, with their heads turned toward each other, whilst at the same time uttering their shrieking, clamorous cry. The motion, however, is often continued after the cry has ceased, and this we might expect if the birds took any pleasure in the brilliant gleam of colour which each presents to, and, as it were, flashes about in front of the other. The effect of this it is not easy to exaggerate, and if it is extremely noticeable to an onlooker at some little distance, what must it be to the bird itself, who looks right into the almost scarlet cavity? We have only to think of the inside of some shells, or of a large, highly-coloured flower-cup, to understand the kind of æsthetic pleasure that may be derived from such a sight.
Similar, but much more striking, is the nuptial behaviour of the fulmar petrel. A pair of these birds lying near together, on some ledge or cranny of the rock, will, every few minutes, open their bills to the very widest extent, at the same time blowing and swelling out the skin of the throat, including that which lies between the two sides of the lower mandible, until it has a very inflated appearance. In this state they stretch their heads towards each other, and then, with languishing gestures and expression, keep moving them about from side to side, uttering whilst they do so, but by no means always, a hoarse, unlovely sort of note, like a series of hoarse coughs or grunts, as though in anger—and indeed, it is uttered in anger, too. But though these motions, with the distension of the jaws, always, as far as I have seen, accompany the note when it is uttered, yet they are often continued afterwards, and sometimes commence and end in silence, so that one has to conclude that they are themselves of importance, and may have as much, or even more, to do with the expression of the bird's feelings as the vocal utterance has.
It is difficult to give an adequate idea of the strange, lackadaisical appearance which these birds present while acting in the above-described manner. With widely-gaping bills, swelled throats, necks stretched out, and heads moving slowly all about, now up, now down, now to this side, now to that, they look sometimes "sick of love," like Solomon, and sometimes as though about to be sick indeed—in fact, on the point of vomiting. All the bird's actions are peculiar, but none more so than this wide gaping distension of the mandibles, with the full view that it offers of the whole interior cavity of the mouth. This last is not indeed brilliant, as is that of the kittiwake, but, for all that, it is very pleasing, of a delicate mauvy blue, æsthetic in its appearance, and in harmony with the soft and delicate tinting of the plumage. There is no reason to suppose that the latter beauty is unappreciated by the bird itself, when seen in the opposite sex. Why, then, should the pale mauve or blue of the inside of the mouth—this purple chamber flung open for inspection during the season of courtship or of nuptial dalliance—be not appreciated too?
The razorbill's mouth, inside, is of a conspicuous light yellow, which, when exposed suddenly to view, contrasts very forcibly with the black of the beak and upper plumage. In dalliance these birds throw the head straight up into the air, and, opening their clean-cut bills, so that one sees the gay interior like a line of bright gamboge, utter a deep guttural note, which is prolonged and has a vibratory roll in it, like the cry of the gorilla when angry—si parva licet componere magnis—as described by Du Chaillu. It is not loud, however, and so is easily lost amidst elemental sounds and the cries of other birds. The vibratory character of the note becomes more marked under the influence of excitement, and the mandibles themselves vibrate as they are opened at intervals, somewhat widely. In the midst of their duet the pair toss their heads about, catch hold of each other's beaks, and give quick little emotional nibbles at the feathers of their throats or breasts. If we can suppose that the birds are interested in each other's appearance whilst thus acting—that they admire or are sexually excited by one another—then it would be strange if the bright flashing yellow so constantly exhibited did not play its full part in producing this result. Imagine ourselves razorbills, and thus acting. Could we be bind to such revelations? I think not.
The pretty little black guillemot—the dabchick of ocean—may often be seen sitting in a niche of the cliffs, and calling to another—its mate presumably—either above or below it. The cry is, for the most part, a weak, twittering sound, but occasionally rises into a very feeble little wail or scream. All the while the bird is uttering it he keeps raising and again depressing his head and opening his beak so as to show conspicuously the inside of his mouth, which is of a very pretty rose or blush-red hue, almost as vivid as that of the feet. The beak is opened more widely than would seem to be necessary for the production of the sound, as if to show this coloration, even though, for the moment, there may be no other bird there to see it. If, however, the rosy inward complexion were in any way an attraction, it would be natural for a bird, wanting its mate, to associate the wish with the action of opening the beak, just as a lonely dove in a cage will coo and bow as to a partner. As a matter of fact, the crying bird very soon flies to the other one (or vice versâ), and, standing beside her, utters his little twitter as a greeting. She, being couched down, responds by raising her head, so that the tip of her beak touches, or nearly touches, his. Then he couches also, and sitting thus, side by side—comfy on the sheer edge of the precipice—the two turn, from time to time, their heads towards each other, open their bills, and twitter together. Every time they open them the pretty rose tapestry of the mouth-chamber must be plain to each or either, and the more so that they are vis-a-vis.
In all these four birds, therefore, we have a nuptial habit of distending the jaws, side by side with a brilliant or pleasing coloration of the region which, by such action, is exhibited. Moreover, in the case of one of them, more particularly—viz. the fulmar petrel—this distension may be unaccompanied with any note, though it always is with the odd gestures and lackadaisical expression which I have tried to describe. In other words, the beak is sometimes opened as a part of the bird's nuptial actions, and not merely with a view to the production of sound. That originally this alone would have been the motive of its being so can hardly, I suppose, be doubted, but may it not be possible that the eye has gradually come to share in a pleasure which was, at first, communicated through the ear alone, and that a process of selection, founded, perhaps, on some initial freshness of colouring, has in time produced a special kind of adornment? If this were so, we might expect that some of the birds so adorned would have the habit of opening the bill in this manner without uttering any note at all, or, at least, that they would very frequently do so. Such an instance we have in the shag, that smaller and more adorned variety of the cormorant, which is much more common on our northern coasts than the so-called common one. One of the most ordinary nuptial actions of these birds is to throw the head into the air, and open and shut the beak several times in succession; and sometimes they hold it wide open for several seconds together. Each time, as the jaws gape, a splendid surface of bright gamboge yellow is exhibited, which the human eye, at any rate, has to admire, and which exactly matches with the naked yellow skin at the base of the two mandibles on either side, where they become lost in what may be called the bird's cheek. This exterior brightly-tinted surface is continuous with the interior and much larger one, and my view is that the colour of the latter represents an extension of that of the former, by a similar process of sexual selection. There is no doubt whatever that this outward adornment largely adds to the handsome appearance of the shag, and probably those naturalists who believe in sexual selection at all will think it as much due to that agency as the crest and the sheeny green plumage. But if the closely similar colouring of the adjacent interior region is to be looked on as merely fortuitous (we escape here, thank heaven, from the all-pervading protective theory), why should the other be thought to be anything more? If the shag had not this habit of opening its mouth and thus displaying what is, in itself, so very striking, it would be difficult, I think, to accept sexual selection as an explanation even of the facial adornment, since, if the one effect were non-significant, so might the other be. As it is, I can see no reason why it should not have brought about both.
I have often watched shags thus throwing up their heads and opening and shutting their jaws at one another, and though I have generally been fairly close to them I have never heard them utter a note whilst so doing. I consider these actions—together with other still more peculiar ones, which they indulge in during the breeding season—to be of a sexual character, and, if so, this silent and oft-repeated distension of the jaws must have some kind of meaning. The large and brilliantly-coloured surface which is thus displayed supplies this meaning, as I am inclined to think.
The fact that some birds—I have not the knowledge to say how many—which do not open the beak in this way, have yet the inside of the mouth brightly or conspicuously coloured, may seem to throw doubt on the theory here advanced; but of course sexual selection is not the only power which may have produced such coloration, and the likelihood of its having done so is decreased if there is no outer facial adornment to match that within. The cuckoo is one such example, for—I speak on the strength of young ones which I have seen in the nest—the whole of its inner mouth is of a really splendid salmon colour. When approached, the nestling cuckoo assumes a most threatening attitude, alternately dilating and drawing itself in, now receding into the nest, now rising up in it as though to strike, having all the while its mouth wide open and hissing violently. Its feathers are ruffled, and altogether it has a quite terrifying aspect, to which the triangular flaming patch that seems to burst out of the centre of it—for the head is drawn right back upon the body—very largely contributes. Especially is this so when, as is mostly the case, there is considerable shadow in the recess of the nest, amidst the surrounding foliage. If it can be supposed that the large false head and painted eyes of the puss or elephant hawk-moth caterpillars have been acquired as a protection against enemies—as to which see Professor Poulton's interesting suggestion[1]—then it certainly seems to me more than possible that the flame-like throat of the young cuckoo has been developed in the same manner, pari passu with the loud, snake-like hiss and intimidating gestures. In conclusion, I would suggest that the bright or pleasingly-coloured mouth-cavity which some birds possess may have a distinct meaning, and be the product either of natural or sexual selection.
AERIAL PIRACY
- ↑ The Colours of Animals (International Scientific Series).