The Way of a Bird
THE flight of birds has kept mankind wondering from the beginning of days; and the wonder has crept into the literature of most countries since Solomon selected ‘the way of an eagle’ for first place in his four miracles of the world. He thought so much of it that he classed this physical wonder with spiritual wonders; and perhaps years before he wrote men felt that flight, had something angelic in it — as the mediaeval artists also persuaded us. Did not the first of great poets use ‘winged’ as his highest praise even for words?
This age-old wonder remained vague and quite failed to penetrate to the secrets of the mechanics of flight till our own times, till the first human flight in a machine heavier than air was made at Dayton, Ohio. The first flyers, especially the brothers Wright, had watched the flight of birds as studiously as ever did old Daedalus, whose son Icarus was the first (mythical) victim. Many men of science, especially in France, had attempted to investigate the mechanics of the motion, not without success; but they were all baffled — the key was not discovered. Mr. Wilbur Wright, discussing with the writer the relation of man’s flight to birds’ flight, once went so far as to say that his years of watching taught him nothing until he himself could fly. Then he began to learn a great deal from the birds, and a score of little puzzles in the manner and habit of the bigger birds were solved. But even then what he learned was as much about the air as about flight.
The essence of the new manifestation was the use of upward currents of air by creatures in control of apparatus that we call an inclined plane. The winds of heaven move heavenward, as well as horizontally between heaven and earth. Their course is also diagonal or vertical, and only those who have traffic in their conflicting motions know what uses the many angles may serve. The birds know, instinctively and through their delicate senses. For a bird is ‘subdued to what it works in.’ Quite literally birds are of the air aerial. Even their bones are partly composed of air bubbles. Mr. Wright believes that some birds create the upward current on which they float.
One of the most characteristic birds of the American continent is the buzzard. It is known to urban as well as to rural dwellers; and there is that about its style which irresistibly draws the eye. It loves to fly in short circles, not the long, difficult spirals dear to the lark, and in this it very much resembles ‘the whistling eagle,’ so called, that is the most characteristic hawk of Australia. The lark seems to climb steep golden stairs under the impulse of an ecstasy of energy inspired by song and love. It makes the long loops to overcome some of the troubles of ascent, and never for a moment limits or arrests the speed of its wing-beats. It threshes the air as a dolphin threshes the waters, cleaving the buoyant and yet resistant medium by the exercise of mere muscular power. The buzzards sometimes rise in short spirals, but thereafter revolve, preferably two or three in company, in more or less level circles, with a scarcely credible economy of effort. Their spacious wings, singularly broad at the tips in comparison with those of most birds, move lazily at long intervals. How can a creature weighing some pounds possibly support such a burden so easily? It seems to be a true theory that their circling, though it may not create, yet maintains and assists a natural upward current; and this is firm enough to support them if the plane is cunningly directed to the exact angle of the draft. How very straight upward the air may move we all can see who have watched a cumulus cloud form. As the water condenses round the cold ascending current, the cloud builds its successive stories, as in a Chinese pagoda.
The circling of the buzzards is an extreme example. They seem to float round and round and delicately tilt their angle for mere pleasure in the exercise of their art. It is my belief that they are particularly fond of flying over American towns, because the high buildings and open spaces — perhaps also the heat generated in the polished streets — assist in the formation of the upward movement of the wind. When we have perceived how a line of elm trees will throw the air upward, how a ‘pool of silence’ is formed on the leeward side, how the sound carried on the wings of this tilted wind becomes audible again only when the draft descends — when we consider such phenomena as these, it becomes a simple inference that the architecture of a town would offer stronger, higher barriers than that of the country, and therefore produce sharper variations in the pattern of the wind.
The upward draft is the secret of all the gliding flight of the long-winged birds. The albatross in its several species is the master artist, but all gulls have high skill. If we divide birds into two classes — and all classifiers have a certain affection for such dichotomy — the gulls are best taken as the representatives of the wide-winged, lightbodied gliders, and the ducks of the heavy-bodied, short-winged, strongengined flyers. The lesser or the greater albatross will glide interminably, even within a few feet of the surface of the sea. And if you watch an albatross closely you discover two things: that the neighborhood of the ship is a help; and that the rougher the sea, the longer it can pursue the ship without moving its wings. The wands may be compared with the grain of a piece of rather gnarled wood; and by subtle instinctive adaptation of the angle of the plane to the changing direction the birds can use the moving air very much as a sailing ship, which, if need be, can go a point or two into the wind. There are some who believe that the aibatross sleeps in the air, suspended high up like a balloon, which is lighter than air. The bird, of course, being heavier than air, cannot merely float; but it is at least probable that even in sleep it can subconsciously preserve its balance, and address itself to the right angle, for any continuous wind will support indefinitely an object slightly heavier than air if it is directed against a broad plane appropriately sloped. It may do much more than this, even when observers are little conscious of its strength. In Switzerland, throughout the Alps the valleys are deep and often wide at the base, narrowing and growing shallower toward their upper parts. The commonest birds are a chough-like species of crow, a family that combines many of the qualities of both gull and duck. You may again and again watch these birds sweep triumphantly upward without stirring a wing. They keep well within the chimney-flue of the valley and find there currents of a rapidity quite unsuspected by the observer watching from some plane at the side of an upper peak. Heavy though they are, they shoot upward like down or bubbles or mere feathers. Tennyson wrote better than he knew when he described the rooks as ‘blown about the windy sky.’
All airmen know that it is safer to fly high than low; as Wither wrote, in an onomatopœic line that delighted Charles Lamb: ‘The more he makes wing, he gets power.’ How well the labored monosyllables suggest the pains of climbing! Ascent is hard; but movement becomes a comparatively easy business when at any moment you can attain what speed you will by planing downward in any direction. It is the ascent that is the trouble: Superasque evadere ad auras, hoc opus, hic labor est.
C’est le premier pas qui coûte. It is at this point that the heavy shortwinged birds that spend most of their life on the ground or water greatly excel the rest. They need and have developed quite other virtues and properties. The engine matters more and the plane less. To save themselves from the commoner dangers they need first of all capacity to accelerate; and since they are not particularly fitted to use the wind, they have developed powers of defying it. It is a liberal education in power to watch a duck of almost any species or variety bore through a tempest. The bird seems to enjoy driving into the very teeth of it, like a steamer escaping from a lee shore. I have seen them on the east coast of Britain come up against a west wind of twenty to thirty miles an hour at an absolute pace somewhere near the equal of the wind they charge. Anatomically, the shortness of the wing and the weight of the body vary in rough proportion with the power of the sinews that hold the socket of the wing. The weighing of the ‘elevator’ muscles by some aeroplane pioneers brought out this point. The duck resembles the oak tree, which, defying the laws of gravity, compensates for the horizontal spread of heavy-headed boughs by the exceeding toughness of its fibre. As an engine the duck’s wing is almost incomparable, though in certain details it is excelled by the pheasant’s.
An old controversy hangs around the subject of the fastest bird. The prize used to belong, at least in the opinion of sportsmen, to that little and most typical duck, the teal. So far as I have been able to collate the evidence and compare it with personal experience, the very fastest birds belong to the classes which come between the gulls and ducks. The peregrine falcons and some of the swifts compete for the head of the list; and it is worth notice that the swifts, which people in general class with the swallow tribe, thanks to several real and obvious likenesses, are put by the classifiers as cousins of the hawks. However this may be, it remains that the ducks attain a dazzling speed and can defy the winds better than any bird that flies, though their momentum exaggerates their difficulty in changing direction. But so much depends on the engine that when it is in the least out of gear, when it is not tuned up, as happens at the early moult, they cannot fly at all; they become an animal of land or water, relapsing into the state of their primeval ancestor.
It is interesting to compare the duck as a flyer with the European partridge. The partridge too has a rather short, broad wing, slightly cupped, and is provided with very strong sinews. Being a ground bird it needs, for defense, skill in rapid acceleration. The noise a covey makes in rising is some indication of the speed and power of the wing-beat. But the species has found the ground so congenial, has learned to run so fast, that the wings have not wholly responded to the growing weight of the body. In spite of the high speed that the bird reaches, it rarely flies so far as a mile and it tires rapidly. Now and again it has been blown off the coast by a strong wind and carried across the English Channel, to fall exhausted on the shore. There is an accredited instance of the birds being picked up by hand on the south coast of England, as weary and careless of enemies as sometimes are the smaller migrants after a journey of five hundred miles and more. The partridge has affinities with another short-winged bird, the pheasant. Some few of them, as one subspecies on the west coast of Africa, have almost lost the power of flight, and escape their enemies, like the ostrich, by speed of foot; but the majority of pheasants are a good example of the short-winged, quick-flapping bird, further endowed, by the length of the tail, with a tolerably efficient plane. Often I have seen the partridge and the pheasant flushed together. For a few short yards the partridge gains, but the superior ‘stream lines’ of the pheasant soon tell, and after two hundred yards the bird with the better plane leaves the other far in the lurch.
The power of acceleration, the possession of a strong engine, implies the ability to rise at a sharp angle. We have all noticed how differently birds start their flight. That splendid flyer the rook — or, indeed, the crow or any of the corvine family — likes to hop along and lift itself as deliberately as Mr. Wright’s very first aeroplane. The snipe, which was often called in the old chronicles ‘the eccentric snipe,’ likes to face the wind, prefers to be blown upward; and quickly though it mounts at a later stage, it travels at a very slight angle for the first ten yards or so. The pheasant can perform miracles of abrupt rising, a power perhaps developed by the need of escaping from vermin. Are there any birds that can so nearly approach the vertical at the opening of a flight? They will fly through the upper branches of a high tree at the foot of which they are flushed. The mallard is perhaps a near rival. Suddenly disturbed in a small pond closely hemmed in by the trees of a wood, it will lift straight through the opening without the necessity of threading the branches of a single tree. The speed of both, though it does not appeal to the eye, is very great considering the foot-pounds that it must lift. How many sportsmen it deceives! Either pheasant or duck so flushed will escape the gun of the very elect, if they do not consciously take note of the angle. Some surprising examples of a bird’s immunity in such circumstances are found in the sporting annals. If it were a question of attaining the altitude of a hundred feet, the blackheaded gull would probably travel at least three times the distance of the route taken by the Mongolian pheasant. It is a common occurrence for a gull to be drowned in stormy weather; and the fatality is due, we may surmise, partly to the wind’s purchase on the extensive wing-surface, partly to the bird’s inability to leap out of the danger of a sudden wave.
Most of the small birds in most countries conform more nearly to the duck type. They can start quickly in any direction, but there are certain exceptions and every degree of special adaptation. The starling is a fine flyer, in spite of its weight of body. At the same time it is a great imitator of the gulls. The two qualities appear ludicrously on some reaches of the Thames in and about London. Gulls have learned to delight in the town, where they find plenty of food to pick up from the surface of the river. The starlings, having watched them with envy, have now taught themselves the same trick. But what heavy weather they make of it! Their wings move at an absurd pace. Instead of gliding at a delicate angle and taking the morsel in their stride, as it were, they flutter abruptly downward, flapping furiously, and by dint of intense muscular effort stay still just long enough to pick up the morsel; but they fail perhaps as often as they succeed.
The swallows and swifts may be said to be the only small birds in the gull division; and they have gifts very nearly peculiar to themselves. The body and skeleton have been lightened by an elaborate apparatus of air sacs, as if nature were striving to produce a craft lighter than air, a tiny airship. This form of adaptation, common in some degree to many birds, has reached its highest development in the swallows, and, accompanied by a wing of considerable length and a tail that is both rudder and plane, it gives them an ease and grace quite their own. They can glide so low as just to dip their wings in the cool water. They can turn and twist with a smoothness that hides the sharpness of the angle. The upper air or lower air is all the same to them. They are so conscious of their mastery that, tender though they are in beak and body and claw, they will chase and mob any enemy. I have many times watched them compel the retreat of a cat by diving at him so close as, you would swear, to touch his ears. The cat did not so much as attempt to strike, and soon retired utterly cowed. We have all seen them mobbing birds of prey and curvetting round them, in repeated arcs, having no trouble to keep pace, though they travel many times the distance. The point has been made by Oliver Wendell Holmes in a charming, if rather elaborate, metaphor, in which he compared their excursions with the thoughts of a nimble-witted listener to a slow preacher. He could wander pleasantly in this direction and that, yet be sure of keeping the thread of the preacher’s journey when he might wish to return.
A considerable number of the birds with which we are most familiar seem to desire to be both gulls and ducks. No pattern of flight, for example, is more distinctive than the woodpecker’s. He proceeds, as do many of the finches, in a succession of loops or festoons. At any period of active flight he ascends a little, and at every pause he is carried downward by the weight of his body. He loves to plane, but is able only to taste the pleasure of the interminable glide of the albatross. There is reason to think that the starling is progressing in the new art, is becoming more of a gull if not less of a duck.
Some few birds, such as the West African pheasant mentioned above, and perhaps too the extinct dodo of Madagascar, after acquiring wings, by slow development, have degenerated in wing-power owing to a peculiar set of local conditions; but wings were, of course, a late development in the story of evolution. The flying animals, of which there are three classes, — insects, bats, and birds, — all changed other organs into instruments of flight, and reached much the same goal by very different paths. Mechanically, and in some directions, the birds’ path has not been the best. The dragon-fly, which has a different mechanism from other insects, is certainly the most able of all the aerial acrobats. Its flight is rapid, and its power of changing direction (a point in which the ducks are peculiarly incapable) is so good that it can dart backward as well as forward. We admire the ingenious flights and sallies of the wagtails in pursuit of insects. The small species seen over English lawns and the larger seen on Australian sheep-stations have an incomparable rudder in the long, flexible tail; but how slow and clumsy is the combination of rudder and wing compared with the twin, perfectly socketed and muscled wings of the dragon-fly.
The quickest of the small birds can scarcely exceed thirteen beats a second. The insects attain to 330 (in the housefly) or 190 (in the bee), and this speed of beat means what one of the writers on games calls ‘ instantaneousness,’ a promptness of alteration in direction of which no bird is capable. Indeed, the insects’ nearest rival is the bat. Nevertheless the bird has done most with its gift of flight. It learned the art, we may presume, by gliding from the trees to which it had retreated to escape from the dangers of the ground. Anatomically, it has been demonstrated that while the bat is theoretically liable to breathlessness, like other quadrupeds, or like the man who runs or swims against the handicap of his lungs, the bird actually evades breathlessness by means of motion. The stress is on expiration, as Professor Thompson has shown, not inspiration; and the mechanism of flight, operating on the otherwise inelastic lungs, keeps the bird in breath, assures the rhythm of aeration.
The spiritual and material truth is that the bird has sublimated its whole being by attuning it. to this newborn power. No animal leads an intenser life. Its heart beats quickly. The blood that gives it animation is arterial and the temperature high. The brain is large. The senses of seeing and hearing are acute and the wits alert. Spiritually many birds have attained to monogamy. Their loves are truly lyric, to use Browning’s adjective; and between the bouts of recurrent parenthood are long spaces for the enjoyment of the free play of a wider life, for change, for the ecstasy of the migration flight.