Chapter VI: Courtship Among Birds (2)

Cranes are much given to dancing. Mr. Nelson, an American ornithologist, has described with much vigour the dancing of the Sandhill Crane in Alaska. As he lay in a “hunting-blind” he was suddenly aroused by the arrival of a crane, followed speedily by a second, uttering his loud note as he came, until he espied the first-comer on the ground, when he made a circuit and dropped close by. Both birds then joined in a series of loud rolling cries in quick succession. Suddenly, the last-comer, which seemed to be a male, wheeled his back towards the female and made a low bow, his head nearly touching the ground, and ending by a quick leap into the air. Another pirouette brought him facing his charmer, whom he greeted with a still deeper bow, his wings trailing loosely by his sides. She replied by an answering bow and hop, and then tried to outdo the other in a series of spasmodic hops and starts, mixed with a set of comically grave and ceremonious bows. The pair stood for some moments bowing right and left, when the legs appeared to become envious of the large share taken in the performance by the neck, and then would ensue a series of skilled hops and skips, like the steps of a minuet. Such antics are characteristic of the Cranes of all species, and sometimes a whole flock will join in such dances. But, it is to be noted, they are not necessarily signs of the _furor amantium_: they certainly always accompany this, but frequently they are indulged in, apparently, solely as an outlet for exuberance of feeling.

Before the theme of dancing can be dismissed the performance of a small species of perching bird, one of the South American Manakins, must be described. The natives call it the “Bailador,” or dancer. In an account of his travels in Nicaragua Mr. Nutting tells us: “I once witnessed one of the most remarkable performances it was ever my lot to see. Upon a bare twig ... at about four feet from the ground, two male ‘bailadors’ were engaged in a song and dance act that simply astonished me. The two birds were about a foot and half apart and were alternately jumping about two feet in the air and alighting exactly on the spot whence they jumped. The time was as regular as clockwork, one bird jumping up the instant the other alighted, each bird accompanying himself to the tune of to-le-do—to-le-do—to-le-do, sounding the syllable to as he crouched to spring, le while in the air, and do as he alighted. This performance was kept up without intermission for more than a minute, when the birds suddenly discovered they had an audience and made off.” Here again we have no evidence of the _furor amantium_; nor that any females were spectators of the scene.

It is important to notice that Mr. Howard, in the course of his study of the Warblers, witnessed a performance having some likeness to this on the part of three young Sedge Warblers but newly escaped from the nursery. And this not in some solitary instance, but on several occasions. Just after leaving the nest, he remarks, they are very playful, “their games sometimes taking the form of a tilting match. Three take part; two sit on convenient twigs facing one another, and the third, from the central position, might almost be called an umpire. Numbers One and Two lower their heads, each in anticipation of the other moving; one of them, call him Number One, then springs into the air and darts at Number Two: Number Two dodges and occupies the position vacated by Number One; each of them then faces round ready to continue the fray, the change of positions becoming quite rapid.” But no recurrence of these antics has been noted during the course of the adult sexual display, which is confined to posturing and displaying the outspread wings and tail. Nevertheless there can be no doubt but that such games in later life are incorporated, in the case of many species, with the love display.

That the reproductive glands have played, and still play, a by no means unimportant rôle in Evolution is shown by the history of the secondary sexual characters. Among the birds, at any rate, the early stages of physical changes belonging to this “figuration” are to be seen in various forms of posturing, which in their more elaborate developments we call “dances.” In many cases, as for example among the Warblers, the periods of sex-emotion are marked by posturing alone. But in a number of species, as has already been shown, the products of the sexual gland seem to have undergone some further elaboration which has resulted in the additional phenomena of gaudy coloration, in hypertrophied plumes, and in weapons of offence.

But not yet is the list of such sexual products exhausted, for no mention has so far been made of the development of the many wonderful devices for the production of peculiar and arresting sounds, musical and otherwise. These are of two kinds: one wherein certain feathers have been modified to produce rhythmical notes either by percussion or by vibration; the other wherein the internal organs have been modified to produce musical notes or loud, resonant cries.

Instances of the latter kind are innumerable, and as a consequence no more than one or two can be cited in these pages. The facts associated with the production of vocal, as distinct from instrumental, music are both curious and puzzling. To begin with, this music is produced by the lower end of the trachea or windpipe, which has become modified in various ways, though not so strictly in relation to the sounds produced as is commonly supposed. The anatomical details of these modifications cannot, or rather need not, be described now, save in the most general terms.

Briefly the syrinx, or organ of voice, of birds, is formed in part by the lowermost rings which form the tubular windpipe, and in part by the smaller pair of tubes which, running therefrom to the lungs, form the bronchi. These last are formed of semi-rings only, the inner wall of the tube being formed by very delicate translucent membranes. As air is forced from the lungs along the bronchi and up the windpipe, the modulation of the voice is effected by muscles which regulate the amount of air driven through the syrinx, and the height of the column in the tube; the latter being effected by muscles which alternately lengthen and shorten it.

So far so good. Next it is to be noted that this syrinx presents a great variety of modifications, or types, differing not only in plan, but also in the number and distribution of the muscles for its manipulation. The most accomplished performers are to be found among that great group of birds known as the Passeres, or perching birds, wherein the number of these muscles is never less than five pairs, and generally rises to seven. This association of musculature with performance is exactly what we should expect. In Nature, however, it is always the unexpected that happens. In the first place, the females are, so far as the dissecting-knife and the microscope can show, as well provided as the males, yet they do not sing. In the second, the Nightingale and the Crow are equally endowed, so far as we can discover, yet it is unnecessary to state that the talents which the Crow possesses are never used! More disconcerting still is the reflection that the Parrot, which is far less generously endowed by Nature in so far as singing muscles are concerned, is a much more skilful performer, inasmuch as it will reproduce with equal fidelity the human voice and the song of the Canary! The latter feat, at any rate, has been accomplished with amazing accuracy both by the little Budgerigar (_Melopsittacus undulatus_) and the Quaker Parrot (_Myopsittacus monachus_). In their wild state the Parrot family are notorious for their discordant cries. It is therefore the more remarkable that such feats should be capable of attainment. But wherefore the elaborate syrinx of the Nightingale, if the simple type seen in the Parrot is capable of the same result, and why the elaborate syrinx in the case of the Crow, which never attains to a greater perfection of vocal effort than the wild Parrot?

One speaks of the syrinx of the Parrot as of a simpler type because of its feebler musculature and the lesser complexity of its framework, but it is nevertheless a more efficient instrument, since it is capable of reproducing both the human voice and songs such as that of the Canary. This fact becomes still more remarkable when we reflect that the natural voice of the Parrot, as we have just remarked, attains to no more than a harsh screech. How is it that, capable of so much, it has achieved so little? The same question may be asked in the case of the Raven. This bird has a syrinx indistinguishable from that of the Nightingale, save in point of size; yet the Raven’s voice is never musical, nor can it be trained to such an achievement. Like the Parrot, however, it can be taught to speak, though its vocabulary is never so extensive. One would have imagined that when the syrinx of, say, the Raven, or any of the Crow tribe, was compared with that of the Nightingale or the Skylark, some structural differences, commensurate with the difference in performance, would be discovered; but such is not the case.

What interpretation are we to place on these paradoxical facts? One cannot help asking why seven pairs of muscles should have been produced by one group of birds to perform what can as easily be achieved in another by two? It is true that the more generously endowed species are musicians by birth, the others only by training. But one cannot make a silk purse out of a sow’s ear. In like manner one asks why male and female, possessing precisely similar voice-organs, should not sing equally well, but they do not. Evidently mere mechanism does not alone answer these questions.

Some, perhaps, may see in them instances of what is known as “Hypertely,” wherein the bounds of mere utility seem to be transcended. Hypertely, however, implies something more than this: it implies a shooting beyond the mark, the overdoing of a feature, where the momentum gained, from some obscure cause, keeps on being increased by cumulative inheritance: and not being checked by Natural Selection, causes the species in respect of such characters to pass beyond its congeners. Professor Lloyd Morgan’s theory of “over-production” would seem better to apply here, though in a somewhat different sense from that used by him. For in the instances just quoted there is a latent potentiality for response to new demands which the struggle for existence may make, but a potentiality varying in degree, and here selection finds its _métier_.

Yet further illustrations of secondary sexual characters, such as are concerned with vocal music, must now be considered. The discussion of these has been designedly deferred. They embrace instances of voice production more singular than any yet referred to, and if possible more difficult to interpret.

The facts first to be reviewed concern the syrinx of certain of the Anatidæ. It is noteworthy that each of the three divisions of this group—the Swans, Geese and Ducks—contains species in which either the syrinx or the windpipe has acquired some singular feature. In the surface-feeding Ducks, modifications of the syrinx are most frequently found. Commonly, as in the Mallard, this takes the form of a spherical bony case; in the diving Ducks this bony chamber has enormously increased in size. Furthermore it has conspicuously changed both in form and character: for it is now roughly trihedral in form, and its walls present large _fenestræ_ closed only by delicate membrane, suggesting that the increased size of the chamber has not been accompanied by a corresponding increase of bony tissue for its construction. Hence all that is available is used for the construction of girders to form supports for the now membranous chamber walls. Some species seem to show that this fenestration has been pushed to excess, leaving only vestiges of this singular chamber, as is shown in PI. 21. In some species the bronchi are much swollen, and the syringeal chamber has entirely disappeared: in others, as in the Merganser and Goosander, a large syringeal chamber is supplemented by dilatations of the windpipe.

GRADES OF EVOLUTION IN THE SYRINX OR ORGAN OF VOICE IN THE MALES OF SURFACE FEEDING AND DIVING-DUCKS.

1. Wigeon. 2. Common Sheldrake. 3 and 4. Red-crested Pochard. 5. Red-crested Merganser. 6 and 7. Long-tailed Duck. 8. Steller’s Eider. 9. Common Scoter.

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Save in the case of the Goosander, these peculiar structures are found only in the male, but in the species first named the male, in addition to the syringeal chamber, has two fusiform swellings in the windpipe, one above the other: in the female one of these swellings is present, but there is no syringeal box.

This box is generally, and probably correctly, regarded as a sort of musical instrument. Nevertheless the males are far less vociferous than the females which have no such voice resonator. One has only to listen to, and compare the notes of the Mallard drake and duck to discover this fact. Here, then, we seem indeed to have a case of “Hypertely.” Before, however, we build too much on this we must discover whether the sibilant sounds uttered by the males do, or do not, play an important part in arousing the sexual passions of the females.

Certain of the Swans and Cranes afford illustrations of musical instruments of an even more remarkable kind. Herein the windpipe at the base of the neck enters a large chamber formed by the absorption of the diploe sandwiched between the outer walls of the keel of the breastbone and the enlargement of the space so created until it can accommodate the tubular windpipe. This, entering the cavity in the form of a loop, runs the whole length of the keel, the upper limb of the loop finally running to the lungs. That we have here an indubitable musical instrument there can be no question, for its possessor is enabled thereby to utter loud, trumpet-like, if harsh, sounds. Here again only the males are so provided.

The profound interest of this really extraordinary association of unrelated structures has never attracted the attention it deserves. Originally, no doubt, one would have met with nothing more than a loop of the windpipe impinging against the anterior border of a normal, blade-like keel: later there would have been formed a broad shallow surface on the keel at the point of contact with the loop, and gradually the depression must have deepened till the bony chamber came into being. By what nexus of sympathy were these reciprocal responses made?

Another very singular type of looped windpipe is that wherein the trachea forms a series of coils between the body and the skin. It is surely somewhat surprising to find that precisely similar coils are met with in widely different groups of birds. Among the Passeres they occur in the Manucode: among the Plovers in the Painted Snipe (_Rhynchea rostratula_): among the game-birds in some of the Curassows, and among the Anatidæ in the aberrant Australian Black-and-White Goose (_Anseranas_).

Very little is really known of the part played by these musical instruments of the Anatidæ, nor, for the matter of that, of most of the “musicians” among birds. Of some of the game-birds more has been gleaned, and among these surely the most interesting is the love-song or “lek” of the Capercaillie. With the advent of April the cock, just before dawn, repairs to some favourite tree—used year after year—and there performs a most astonishing if unmusical serenade; with outstretched neck, drooping wings and spreading tail he gives forth a weird, uncouth kind of song, more or less divisible into three parts. He begins with a series of notes which remind one of nothing so much as the sound made by two sticks knocked together at intervals of ten to fifteen seconds, getting quicker and quicker, and changing in key till at last they become bell-like. Then follows a series of sounds like the drawing of a cork out of a bottle, and these end with bird-like twitterings. By this time, however, the singer has worked himself up to an ecstasy of fervour and passion so intense as to deaden him to all that may be passing in the outer world. During these moments no sound disturbs him, partly, apparently, because the excitement of the “song” causes a turgid condition of the blood-vessels which for the time effectually deafens him. “Sportsmen,” in Swedish and other European forests, knowing this, select such performances as affording the most favourable time for Capercaillie shooting, only cocks being selected.

A survey must now be made of some of the more remarkable cases whereby more or less musical, or rhythmical, sounds are made by instruments of percussion; or by rapid vibrations. These are in almost every instance formed by varying grades of modification in the feathers of the wings or tail. Their presence, and their use, seem natural enough until we recall the fact that many other birds without any apparatus whatever, make sounds in no way less remarkable or less penetrating. Pigeons, Nightjars and Owls, for example, can produce at will curious snapping sounds by bringing the wings smartly together over the back. The White, and Shoebilled Storks make castanets of the beak, throwing the head backwards till the point of the beak touches the back, when the jaws are set rapidly clashing one against another, producing a sound comparable to the “bones” of negro minstrels, but without the varying rhythm. As this performance is proceeding, the head and neck are slowly moved through half a circle, till the tip of the beak touches the ground, when the music ceases. As with the wing-snapping just referred to, both sexes are equally skilful performers; but while they seem to indulge in such exercises much more frequently, and with more vim during the breeding season, they will break out after this demonstrative fashion at all times of the year. But why, then, the need for the yet more elaborate contrivances which are to be met with among the Snipe, the Game-birds, and certain of the Passeres?

However, be this as it may, in a large number of species a special mechanism has been evolved to produce sounds which, as has been remarked, in other species are no less effectually made without that mechanism.

One of the simplest of the cases is that furnished by the remarkable “bleating” or “drumming” performances of many species of Snipe, generally, if not only, when sexually excited, and especially of the Common Snipe (_Gallinago cœlestis_) during its love-flights. Mounting to a great height, this bird, at such times, suddenly turns, and descends with prodigious speed, meanwhile holding the tail fully expanded. The outermost pair of feathers are, however, specially modified so that, in the first place, during this descent they stand at right angles to the long axis of the body and well apart from the rest of the tail-feathers. This alone, however, would not produce these weird sounds, which owe their origin to the fact that these particular feathers have their shafts conspicuously thickened and peculiarly curved, while the vane or web of the inner side of the feather is of great width and structurally differs from the vanes of the other feathers, whereby the vane becomes more resistant to the rush of air caused by the wings during the descent.

But in the case of these Snipe it is to be noted this curious form of musical instrument is found in both sexes, and there is little difference in the quality of the sounds produced, but the bleating of the male is said to be the more resonant.

The Common Snipe is the best performer among several different species, and it is to be noted presents, to a casual examination, no remarkable or peculiar feature whatever—the structural differences just described are only to be discovered by very patient scrutiny. But in the Pin-tailed Snipe (_Gallinago stenura_) the number of the feathers has been greatly increased, while at the same time their webs have been so reduced that the outspread tail seems to consist of little more than spines. With such a transformation one expects to find a quite exceptional performance, far surpassing that of the Common Snipe. Yet so far as observation and experiment go they effect absolutely nothing! Here again we have a case where modification of structure has passed the bounds of need and passed so far as to make the whole tail useless as a sound-producing organ!

A contrast and a parallel are afforded by some of the gallinaceous birds of South America. The Black Penelope (_Penelopina nigra_) of Guatemala, while on the wing, will, during its “love-flights,” pitch suddenly earthwards with outstretched wings, and at such times a crashing, rushing sound is produced, which has been likened to the sound of a falling tree. Yet there is nothing in the shape of the wing which will account for this. On the other hand, a near relation of this bird, the Black-wattled Guan, _Aburria_ (_Penelope_) _aburri_ has the four outermost primaries deeply incised along their inner vanes, reducing the outermost portion of the feathers to mere spines. Yet, so far as is known, this wing makes no especial noise. However, the males of certain little South American Perching-birds known as Manakins have the shafts of the secondary quills thickened to an extraordinary degree so as to form solid, horny lumps, and these, when the wings are brought together smartly over the back, produce a noise not unlike the crack of a whip, so that here again structure and function are found together. In the contradictory cases just cited where specialized parts are found which are apparently functionless, we must suppose that the habit of using them has been supplanted by some new stimulant.

The part played by musical instruments of percussion would seem to be a variable one. In some cases, and possibly in all, it may serve as an excitant, or stimulant, to the rousing of a “sex-storm”; in many, at any rate, such sounds serve as calls to the sexes when separated. This much seems to be demonstrated in the case of certain of the Woodpeckers, which in this matter differ conspicuously from any other species yet referred to, in that they have developed no special sound-producing mechanism, but make use of hollow trees which serve them as drums, the beak being used as the drumstick. This is a very noteworthy fact, for one would have supposed that here at any rate, where the production of loud and far-reaching sounds is of vital importance, the means would have been provided by some such modification of the wing-feathers as we have already seen to obtain in the case, for example, of the Manakins. More closely examined, however, this apparent failure of the organism to produce its own mechanism becomes less remarkable, for Woodpeckers are forest-dwellers and but indifferent fliers; loud sounds produced by the rapid vibration of the wings or tail, as in the case of the Snipe, in mid-air, are thus impracticable, if not impossible, and sounds produced after the fashion of the Manakins would not have sufficient carrying power.

One of the most skilled performers among the Woodpeckers is the Great Spotted Woodpecker (_Dendrocofus major_), whose weird drumming once heard will never be forgotten. These sounds are produced by blows of the beak on a branch, delivered so rapidly that the bird’s head presents but a blurred appearance. The sounds thus made vary with the resonance of the wood and can be heard at a distance of half a mile. These strange vibrating notes are most frequently heard during the courting season, and they will commonly beget a speedy response from some more or less distant part of the wood, so that their purpose is clear. They attain the same end as the bellowing of the stag or the “lek” of the Capercaillie. They are, however, to be heard at other times, as when the birds are greatly alarmed or when the nest is being robbed.