No less remarkable is the performance of the Frigate-bird (Fregata), a tropical species allied to the Pelicans and Boatswain-bird, and to our own more familiar Cormorants and Gannets. It might well be called a marine Swift, having excessively short legs and small feet, and a wonderful expanse of wing. As with the Swifts, of course most of its time is spent on the wing; the feet are only useful for supporting the body when ashore, they are never used for walking, at any rate, for more than a few steps. The wings afford the only means of locomotion. Our knowledge of these birds when under the stress of sexual excitement we owe to Dr. C. W. Andrews, who had the good fortune to study the species known as the Great Frigate-bird (Fregata aquila) during his task of surveying Christmas Island (Indian Ocean).

“About the beginning of January,” he remarks, “the adult males begin to acquire a remarkable pouch of scarlet skin beneath the throat; this they can inflate till it is nearly as large as the rest of the body, and a dozen or more of these birds sitting on a tree with outspread, drooping wings and this great scarlet bladder under their heads are a most remarkable sight. When a hen bird approaches the tree the males utter a peculiar cry, a sort of ‘wow-wow-wow-wow,’ and clatter their beaks like castanets, at the same time shaking their wings. When they take to flight the air is allowed to escape from the pouch, but occasionally they might be seen flying with it partly inflated.”

Here again there can be no doubt about the purpose, or perhaps one should say the stimulus, of this strange performance. This pouch, I have been enabled to ascertain from dissection, is not formed by inflating the gullet, but, as in the case of the Prairie-hen, by the enlargement of the air-sacs of the neck.

These air-sacs, which are present in all birds, are only enlarged to further the ends of sexual display in a few species, and, curiously enough, these are in no way related one to another. The Adjutant storks, it may be remarked in this connection, have used the air-sacs which are fed by the nasal system instead of those fed by the lungs, as in all the species so far described. When deflated this pouch forms a quite inconspicuous conical swelling in front of the neck; under the stimulus of excitement, it awakens as it were into activity, and is suddenly transformed into a great red or red-and-black bag, encircling the neck and projecting far downwards in front of it, only to be deflated an instant later with a speed which leaves one gasping.

The specialization of the air-sacs, that is to say their transformation to perform new functions subservient to the ends of sexual activities, is not exclusively confined to display. In at least one instance an air-sac has been specially developed to act as a voice resonator. This is furnished by the Emu, wherein the wind-pipe, near the middle of its length and on its anterior aspect, has a number of incomplete rings forming a long slit. The lining of the windpipe escapes from this slit in a hernia-like pouch, and takes up a position beneath the skin. Even when inflated this pouch gives no very obvious sign of its existence, but it serves to produce a curious hollow, drumming sound, like the boom of a big drum softly beaten. But why it should have been developed, when the Ostrich and the Cassowary produce similar but louder “music” without any special apparatus whatever, is a mystery. At least one species of Cassowary can emit a roar which would do credit to a lion.

In the males of all healthy animals the periodic stimulus to reproduction finds expression in more or less striking eccentricity of conduct. Sometimes, as the foregoing instances have shown, this has been exaggerated by the development of long, resplendent plumes: sometimes by brilliant coloration, displayed either by the plumage or by bare areas of skin, or by both, while in not a few cases attitudes, to our eyes grotesque and made still more so by the aid of inflatable pouches, are the outward and visible sign of the raging fires within. For the completion of this chapter yet other instances of this kind must be cited, instances which reveal a further elaboration of some of the more striking of these tricks of posturing; or which concern the growth of the aggressive instincts, which are proclaimed by the development of armature often of a very formidable character. As the sequel shows, however, there are no hard and fast dividing lines between these several modes of expression.

That remarkable bird, the Ruff (Machetes pugnax), now, alas! no longer to be met with in our fens, exhibits a curiously composite character in the phases of its love display.

Preparations for this are begun in the early spring by the assumption of what is called a “nuptial dress,” which is worn only by the male, and which contrasts in a very conspicuous manner with the plumage worn during the rest of the year. The most striking features of this dress are the great, erectile, Elizabethan ruff which encircles the neck immediately behind the head, and the long, tongue-shaped “ears” which surmount the head itself. These exhibit a most remarkable diversity in their coloration, and it is no exaggeration to say that no two are ever alike. Red, cream-colour, buff, black, white; spotted, streaked, freckled and barred are the only descriptions that can be applied to them, for the combinations of their hues and patterns seem infinite. Having grasped this fact, the eye next turns to the colouring of the rest of the body, and it will be found that here too is the same diversity, though less conspicuously so; and finally it will be noticed that at this time the feathers around the base of the beak have been replaced by yellow or orange-coloured papillæ. The females also now wear a dress differing from that of the so-called “winter plumage,” but it does not present any very striking features nor any form of ornamentation comparable to that of the males.

The Ruff is a polygamous bird, which, in its display, presents some curious and puzzling features, one of which consists of a sort of tournament between rival males. At the break of day the performers, selecting such eminences as the fen-lands afford, assemble apparently to display their finery, for a couple of males will often stand facing one another with frills erected and beaks touching the ground, silent and immovable, for perhaps half a minute. Sooner or later, however, they will commence to spar, and this presently leads to blows, during which one of the combatants will attempt to seize the other by the wings. However, no damage seems to be inflicted during such encounters, which are by no means aimless or profitless, for during such bouts the weaker, less vigorous birds are driven from the field, and the victor in consequence wins for himself a larger harem.

When the actual pairing time arrives the parade of the frills begins again. The amorous instincts, it is important to notice, are awakened earlier in the males, so that by the time the females have attained to a like condition the least mettlesome males have been driven off. What follows is not the selection by the females of the finest performers so much as a process of sorting out, whereby the females discover and cleave to those males which are readiest for mating. This display succeeds in revealing both the most mettlesome males and the most amorous females, who, however, would seem to require great persistence and much demonstration on the part of the males before they can be finally aroused to the pitch necessary for pairing. Again and again a male may be seen to approach an apparently very unconcerned female, and then to crouch down before her with his beak pressed to the ground and his frill and “ears” set off to their fullest. For some seconds he will remain lost in apparent contemplation, then with a dazed, far-off, expression he will look up, to find, as often as not, that she is still apparently feeding, quite unmoved by his protestations; or that she has even flown off and left him. Pursuit speedily follows, and the performance is repeated until at last she too catches the flame of passion and permits, or rather invites, the final act of sexual congress.

Though these birds on occasion will fight, and savagely, they cannot inflict serious damage on one another by reason of the relative feebleness of their beaks and legs, which are but ill-adapted for violent measures. Inasmuch as the Ruff is a polygamous species, these bloodless battles have a peculiar interest. They show that the preponderance of females, which polygamy implies, is not, as is commonly supposed to be the case, due to a high death-rate among the males by fighting. The same is true of the Wydah-birds, and their kin, the only polygamous species among the Passeres.

In this connection it is to be remarked that fighting, of a more or less sanguinary character, is apparently universal among birds, the conflicts being waged not so much in the way of squabbles for the possession of females as for the acquisition and retention of territory and all that this entails during the breeding season and, to a much less extent, in the defence of the eggs and young. But to this point we must return. For the moment it will be more profitable to focus attention on the character of this fighting. In the first place, it is by no means necessary that the combatants should be armed. The “dove of peace” at this time of the year appears in a new and not always pleasing light, for not only will he fight his neighbours, but he does not always show that gentleness towards his wife with which tradition has credited him. The little Humming-bird would seem to be as little capable of fighting as a bird could be, yet few are more pugnacious. The naturalist Gosse tells of a pair which had torn one another’s tongues out in their blind fury; and everybody knows that Robins and Tits fight savagely to preserve their chosen haunts from invasion by their neighbours. In some birds this pugnacity has become an overmastering passion. Some of the Quails, and a species of Rail (Gallicrex cristatus), a near relation of the Moorhen, are commonly kept by the natives of the East, as our forefathers kept Fighting-cocks, for the sake of seeing them fight one another. Yet, save in the case of the Fighting-cock, neither of these birds possesses any aggressive weapons.

Among the game-birds, however, powerful armature, in the shape of long, pointed, spurs on the legs are met with. In the Jungle-fowls and Pheasants only a single pair are found on each leg, but in other species, as in the Francolins, there are several pairs, and these birds, it is instructive to notice, are notorious for the ferocity of their encounters. It is said that in the Indian Swamp-Francolin (Francolinus gularis) nearly every individual is marked by scars and wounds received in duels with rivals.

Certain members of the Plover-tribe, and certain Anserine birds, have developed spurs of a very formidable character on the wings. Among the Plover-tribe the best example of such armoured species is the Egyptian Spur-winged Plover (Hoplopterus). This bird, after the fashion of its unarmoured relatives, such as the Common Lapwing, fights by turning suddenly in the air and striking with the wings. In the case of the formidably armed Egyptian bird the result is often fatal; but with our Lapwing a fatal result is rare, since but slightly swollen knobs take the place of spurs. In Hoplopterus and in the Jacana this spur arises from the base of the thumb, but in the Spur-winged Goose (Plectropterus) it is borne by one of the wrist bones (the radial) while in the aberrant Geese-like birds (Palamedea and Chauna) there are two spurs on each wring, one at each end of the metacarpus. That these weapons have come into being in response to need seems a very natural conclusion, but it is one which presents many difficulties when more closely examined. The wing spurs, differing widely in their nature as they do, in one case borne on a carpal bone, in others on the metacarpus, seem rather to owe their origin to fortuitous variations which have become, so to speak, adopted by selection, than to a response to the oft-repeated stimuli incidental to fighting. The latter explanation is Lamarckian and to-day finds favour with but few. The stimulus theory seems to be effectually discounted by the existence of the spurs on the legs of gallinaceous birds. That these owe their origin to impacts, or blows, seems more than doubtful: and one can hardly see how they could have served any useful purpose until they had attained a sufficient length to serve as weapons. Even if we suppose that the spurs of, say, the Jungle-fowl or the Francolin have been derived from tuberosities such as are found on the legs of the French Partridge (Caccabis rufa), we should still lack evidence that the use of the legs in fighting caused the origin of the tuberosities.

There is yet another puzzling feature in regard to the armature of the wings, and one which may yet help to a better understanding of the puzzles presented by spurs. A Jacana, one of the Plovers, has the radius broadened or flattened out from its middle onwards to form a flat plate or blade, but the use thereof is unknown. It may possibly serve as a weapon of offence, enabling the bird to beat its rivals with its wings, but from the nature of the structure, and of the effect such a use of the forearm would have upon the hand, it seems doubtful whether it serves any aggressive function. If used at all in fighting it is probably during fights in mid-air, when, after the fashion pursued by the Spur-winged Plover, and even in the case of our own Lapwing, a blow is struck by the uppermost bird at its rival, and often with fatal effect. It is significant to remark, by the way, that in the Lapwing a tubercle answers to the spur of Hoplopterus just as the tubercles of the French Partridge (Caccabis) answer to the spur of the Jungle-fowl or Pheasant: but the flattened radius of the wing of the Metopidius jacana has no parallel.

With birds, as with men, there must always remain the ability to appeal to force when some important end cannot otherwise be gained. The species which adopts the crazy tactics of the Quaker is doomed to extinction, sooner or later. The foregoing instances display force, as we may say, aggressively. But even the peacefully disposed birds can fight when aroused.

Reference has already been made to dancing in this chapter; but so far no very striking instances thereof as a form of sexual display have been cited. The subject has been deferred because this peculiar type of activity is not always directly associated with the furor amantium.

With some species, which, it should be remarked, also lack distinctive colouring, the erotic state is manifested apparently not so much by the display of expanded wings and tail as by frenzied dances. The Jacanas, aberrant members of the Plover tribe resident in South America, are expert performers, displaying moreover a curious spontaneity during such outbursts. A flock will be apparently sedulously feeding when suddenly and with quick, excited gestures all will cluster together in a group and go through a singular and pretty performance, holding their wings outstretched and agitated, some with a fluttering and others with more leisurely movement, like that of a butterfly sunning itself. The performance over, all scatter and feed again.. The Honourable Walter Rothschild, in his “Avi-fauna of Laysan” tells us of the stately Albatross, which breeds, or rather bred there—for the Japanese display a singular callousness in regard to animal life where commercial interests are concerned in thousands: “First they stand face to face, then they begin nodding and bowing vigorously, then rub their bills together with a whistling cry. After this they begin shaking their heads and snapping their bills with marvellous rapidity, occasionally lifting one wing, straightening themselves out and blowing out their breasts; then they put their bills under the wing or toss them in the air with a groaning scream, and walk round each other often for fifteen minutes at a time.”

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.

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.

CHAPTER VII

THE SEXUAL SELECTION THEORY AS APPLIED TO BIRDS

Where the Rôle of the Sexes is reversed—Polygamy and how it is brought about—Coloration and Courtship—Instinctive Actions—The Importance of Landed Possessions—The Meaning of “Display”—The Springs of “Behaviour”—A New Light on the Wild-duck—The “Display” of the Great-crested Grebe—Some Neglected Factors.

The significance of the varied behaviour of birds—more especially of the males—during the period of reproductive activity must now be more minutely analysed. But before this analysis can be profitably begun, it will be necessary to recall the fact that there are several cases known wherein the rôle of the sexes is largely reversed. Herein the females do the “courting,” and fight one another as rivals for the males; while the males perform the duties of incubation and brooding, and feeding the young. This is really very remarkable, and demands more attention than it has yet received.

What factors have brought about this curious reversal? In any search for an explanation it must be borne in mind that in all such cases polyandry is the rule, and in all such cases the female is larger and more vividly coloured than the male. Here, then, we have exactly the opposite to what obtains in cases of polygamy. What is the reason for this preponderance of males? Why is it that when the males are in excess of the females the latter should be the more brilliantly coloured and the more amorous? These questions at present are unanswerable. When polygamy obtains it seems always to be assumed that it is explained by the excessive pugnacity of the males, which, after fierce contests for the mastery, take forcible possession of as many females as may be captured and held in durance; the same argument seems never to have been applied when polyandry obtains. There can be no doubt but that it applies in neither case.

When polygamy obtains, as we have already pointed out, the females are not seized and captured by the males, they are not victims of a lecherous lord. On the contrary, they seek the males, and the intensity of the desire to satisfy their natural cravings extinguishes any feeling of jealousy.

The same interpretation must obtain where the numerical values of the sexes is reversed. Failure to appreciate this accounts for one of the many futile suggestions made for the suppression of the rabbit plague in Australia, which was that large hauls of these pests should be made by netting, and that the females should be slain and the males released. This, it was held, would lead to the speedy reduction of the latter, which would kill one another in their fights for the remaining females. The plan was impracticable, but the suggestion demonstrated the prevalent belief as to the attitude of the male in this respect. Had it been well founded, surely polyandrous species, whether of birds or beasts, would never have existed; for, by the reduction of the males, monogamy would speedily have been restored. How, then, are we to explain polyandry? How are we to explain the fact, as it seems to be the fact, that the excess of males has brought about such a complete reversal in behaviour—the males, instead of the females, requiring the aphrodisiac? The solution of this problem probably lies with the physiologist. We now know that the problem of sex does not rest merely in the complete development of the primary sexual organs; we know that fertile unions do not depend merely on the act of pairing, but on the functional activity of those ancillary glands already referred to. And it may well be that some change in the character of the secretions has not only altered the numerical values of the sexes, but reversed the normal rôle of coloration and behaviour. That is to say, neither polygamy nor polyandry among the lower animals, at any rate, has been brought about or is maintained by the excessive death-rate due to combats for possession of mates, but must be explained as demonstrating inherent changes in the germ-plasm, disturbing the relative proportions of the sexes and correlated with a profound transformation, not only in the behaviour of the sexes during the period of reproductive activity, but also in their physical characteristics.

The action of the primary sexual glands and of the ancillary glands has, then, to be allowed for in all attempts to interpret behaviour in sexual matters. No less so must this be the case in regard to the development of coloration and other forms of ornament, and the genesis of weapons of offence. But at present we are, in this direction, dealing with an unknown quantity. The recognition of this, however, should not deter us from attempting to solve the riddle of sex from the phenomena which have so far been surveyed.

To-day the interpretation which holds the field is Darwin’s theory of “Sexual Selection.” But this was framed rather to account for the existence of conspicuous secondary sexual characters—the antlers of Deer, the train of the Peacock, and so on; it did not take cognizance of the unarmed, and the soberly-clad individuals. But whatever shortcomings we may discover, real or imaginary, in this theory, we must never forget that he had not only to analyse and present his facts, but he had first to collect them. This, in his case, was a more laborious task than most people seem to suppose. Our criticisms to-day are based, not so much on the revelations of new facts, as on the harvests of his gleaning. Yet when all is said and done, the theory of “Sexual Selection” remains, though perhaps in a new setting.

To attempt to epitomize this theory is to essay a very difficult task. But, in a condensed form, it may be said to be a theory which accounts for the development of secondary sexual characters, on the one hand through the agency of conquest by battle, whereby rival males strive for the possession of one or more females, who have no choice in the matter, or who may deliberately elect to follow the victor: and on the other by display of conspicuous ornamentation, or of more or less grotesque antics, or of some form of music, using this term in a very wide sense. Wherever display is the agent, however, its purpose seems to be to win the affections of the female to whom such attentions are addressed. She is supposed to elect to mate with the finest performers of a number of suitors. In this way, it is assumed, the intensity of the display, whatever its nature, has been gradually increased.

Wallace strongly opposed this, contending that it assumed too much, that it assumed a common and uniform standard of perfection shared by all the females concerned in the selection, which is indeed assuming too much. But his own theory was no more satisfactory. Indeed it was very much less so, for he contended that these various exaggerations of colour and form are to be regarded simply as evidences of a superabundant vitality, though there is no evidence that “superabundant vitality,” if it exists, is a transmissible character.

The revised version of the Sexual Selection theory advanced in these pages is largely inspired by the work of Mr. H. Eliot Howard who, in his Monograph on the British Warblers, has not only added very materially to our knowledge of the life-histories of these birds, during the reproductive period, but has also done much—both in the direction of destructive, and constructive criticism, of generally accepted conceptions on this head—to set us on the right track for further research.

A study of his work leaves one with the conviction that, while these birds exhibit what we may call a nascent intelligence, their actions, on the whole, may be described as instinctive, or congenitally definite. That is to say, they follow one another in definite sequence. Hence we must regard each new phase in the chain of events appertaining to the reproductive cycle, as following one another in a definite sequence, so that any break therein throws the orderly performance of the necessary acts out of gear. There is no realization of what reproduction means, no deliberate striving to achieve that end. Each new phase brings its own set of associations and sets a new train of actions in motion, which are performed mechanically. For instance, these Warblers, like hosts of other species under similar circumstances, are scrupulously careful to remove the fæces of their young from the nest; thereby preserving it in a sanitary condition. It is certain that any neglect to do this would speedily end in the death of the young. This act is “instinctive”; it is not performed because the parents have evolved any views on sanitation, and any strain in whom this instinct was defective would speedily become eliminated. Mr. Howard has demonstrated the mechanical character of this sanitary measure by placing leaves in nests of young. The parents, having fed their offspring, at once seized upon the leaf and commenced to dispose of it after their usual fashion, first by trying to swallow it and then by carrying it away. They did not, evidently, realize the difference between the texture of the leaf and the milk-white, jelly-like envelope which always encloses the fæcal matter of the nestling. We shall probably never know how this most vitally important instinct came into being; nor can we hope to discover what chain of happenings begot the instinct, which each parent displays, to gently stimulate the cloacal lips of their offspring in order to induce the discharge of the fæces when this does not immediately follow the stimulus of swallowing food.

We cannot credit these birds with notions on the importance of the regular discharge of the evacuations. Equally mysterious is the development of the envelope enclosing the fæcal matter. This is jelly-like in substance, and of considerable thickness, and is enclosed within a very delicate skin or pellicle, enabling one to lift the whole in the fingers without soiling them. How and where it is formed should not long evade discovery. But how it has come to be is another matter. We can, at any rate, vaguely account for responses of the organism to internal stimuli reacting directly on the individual, but here is an elaborate mechanism evolved in response to extra-personal needs: and which cannot be regarded as of exactly the same configuration as the instinct to feed the young.

A return must be made to the nature of the early phases in the procession of the reproductive instincts. Mr. Howard’s study of the Warblers seems to show conclusively that these first manifest themselves in an overmastering desire to seize upon territory large enough to ensure an abundance of food for the offspring that are yet to be. To this end the males arrive from their far-distant winter quarters at least a week in advance of the females. Since each returns approximately to the scene of last year’s nursery, the arrivals are fairly distributed at the first; but nevertheless this distribution inevitably brings a conflict of interests between one or more males, perchance young birds about to start in life, and having therefore no definite objective. But whatever the reason, the competition is there. The strongest male remains in possession, and immediately commences to express the ecstasy of feeling which possesses him in continuous outbursts of song. Such, doubtless, answer to the bellowing of the male stag. They advertise the presence of a male to the female, who, as she arrives, would seem to be already stirred by the rising storm of sexual desire, for having once discovered a male in possession of the all-necessary site for the nest, and the equally necessary domain, each settles down to conjugal bliss: within twenty-four hours the task of building has begun. There is evidently here no sexual selection in Darwin’s sense: no choice from among a number of males of the individual which most excites desire within her; but the mating of the most mettlesome, most virile males has been determined before her arrival and by a double sieve. In the first place, the duller-witted birds fail to secure suitable territory, and in the second, the territory, having been taken, must be held by force, so that only the strongest males remain to mate when the females eventually arrive. So far as one can see, selection is less exacting in the case of the females, which apparently need do little more than respond to the advances of the males.