Bird flight

“ The slow, ungainly bird is transformed into a swift and brilliant creature, beaded with globules of quicksilver where the air clings to the close feathers, and flying through the clear and waveless depths with arrowy speed, and powers of turning far greater than in any known form of aërial flight. The rapid and steady strokes of the wings are exactly similar to those of the air birds, whilst its feet float straight out level with the body, unused for propulsion, or even as rudders, and as little needed in its progress as those of a wild duck on the wing. ”

“ And then, in the second place, many of these feathers are most useful in flight. Without them, indeed, a bird could not fly at all. If we want to keep a tame bird from escaping, we have only to clip its wings, and then it can no longer raise itself into the air. But it is not only the feathers of the wings that are used in flight; those of the tail are employed as well, for they assist in flight, especially in checking speed, and serve as a rudder, enabling the bird to steer its way through the air.
Now birds are divided into orders and tribes and families, just as the mammals are. ”

“ I can only account for this magnificent flight, beginning so laboriously, by supposing that the bubble space under the skin becomes inflated with an air lighter than atmospheric air, enabling a body so heavy with wings disproportionately short to float with such ease and evident enjoyment at the vast heights to which the bird ascends. The heavenward flight of a large bird is always a magnificent spectacle ”

“ Every one has noticed a second type of bird flight—soaring. It is this flight which is exactly imitated in a glider. An aeroplane differs from a soaring bird only in that it carries with it a producer of forward impetus—the [Pg 13] propeller—so that the soaring flight may last indefinitely: whereas a soaring bird gradually loses speed and descends.
In a Meteoric Shower
A third and rare type of bird flight has been called sailing. The bird faces the wind, and with wings outspread and their forward edge elevated rises while being forced backward under the action of the breeze. ”

“ Both the soaring and the sailing of birds show them to be proficient in the use of factors employed in aerial transportation that only recently have become understood and imitated by aeronautical engineers. The use of ascending currents of air, employed by all soaring birds, and easily demonstrated by observing the gulls that glide -79- hour after hour along the windward side of a ship, are now utilized by man in his operation of gliders. Moreover, the whole structure of a bird renders it the most perfect machine for extensive flight that the world has ever known. ”

“ Flight, because of the rarity of the air, is infinitely more rapid than either walking, running, or swimming. The flying animal receives support from the air by increasing the size of its travelling surfaces, which act after the manner of twisted inclined planes or kites. When an insect, a bat, or a bird is launched in space, its weight (from the tendency of all bodies to fall vertically downwards) presses upon the inclined planes or kites formed by the wings in such a manner as to become converted directly into a propelling, and indirectly into a buoying or supporting power. ”

“ It is the form and flight of the bird alone that has given man at last the mastery of the atmosphere. Without the bird as a living model we have not the slightest reason to believe that he could have ever learned the mechanism of flight. Now it is the flight of the bird, studied under the American sky, that has given the [Pg 152] nations the war engine that will perhaps rule the destiny of the human race henceforth. The form of the bird will fly before our autumn-brown American armies as they cross the sea—leading them as the symbol of their victory. ”

“ From the moment it rises until it alights again there is no cessation in the rapid vibration of the wings; but, like a ball thrown by the hand, the bird flies straight away with extraordinary violence until the impelling force is spent, when it slopes gradually towards the earth, the distance it is able to accomplish at a flight being from 800 to 1500 yards. This flight it can repeat when driven up again as many as three times, after which the bird can rise no more. ”

“ But, as a matter of fact, the air in which a bird flies is never stationary, as I propose to show; it is always moving either up or down, and soaring birds, by a very delicate sense of feeling, always take advantage of a rising column. If a bird finds itself in a column of air which is descending, it is necessary for it to work its wings very rapidly in order to prevent a descent to the earth.
I have often observed the flight of hawks and eagles. They seem to glide through the air with hardly any movement of their wings. ”

“ Another method, occasionally used, is to descend with the wings about two-thirds open, causing a loud roaring noise due to the wind passing through the separated primaries, and in this case the bird alights directly with spread wings and tail.
The "joint flight" is shared by both sexes and is normal in character, both birds (but especially the male) calling quickly as when rising for the ceremonial flight. The female is generally slightly in front of the male on these occasions. ”

“ This behaviour is expressed in a peculiar flight. The bird rises high in the air, circles round with slowly beating wings above the marsh, and utters a call which, as far as my experience goes, is characteristic of the performance. The air is often full of individuals circling thus even beyond the confines of the marsh, for a male does not limit its flight to a space immediately above its territory; but nevertheless careful observation will show how unerringly each one returns to its own position on the breeding ground, no matter how extensive the aerial excursion may have been. ”

“ In subaquatic flight the long axis of the body of the bird, and the short axis of the wings are inclined slightly downwards and make a backward angle with the surface of the water. The wing acts more or less efficiently in every direction, as the tail of the fish does. The difference noted in the direction of the down stroke in flying and diving, is rendered imperative by the fact that a bird which flies in the air is heavier than the medium it navigates, and must be supported by the wings ”

“ Each flight of starlings seems to have its leader whose orders are instantly obeyed, for every bird in the whole flock swerves, and wheels, and turns at the same moment—a maneuver seen equally in the vast migratory flocks of red-winged blackbirds which gather in autumn on every American marsh and are [260] gradually spreading inland. ”

“ The bird, let loose in eastern skies, [1]
When hastening fondly home,
Ne'er stoops to earth her wing, nor flies
Where idle warblers roam.
But high she shoots thro' air and light,
Above all low delay,
Where nothing earthly bounds her flight,
Nor shadow dims her way. ”

“ Among mammals there are Flying Phalangers, Flying Lemurs, and more besides, all attaining to great skill as parachutists, and illustrating the endeavour to master the air which man has realised in a way of his own.
The power of flight brings obvious advantages. A bird feeding [Pg 88] on the ground is able to evade the stalking carnivore by suddenly rising into the air; food and water can be followed rapidly and to great distances; the eggs or the young can be placed in safe situations; and birds in their migrations have made a brilliant conquest both of time and space. ”

“ The two will then often take wing and fly for a while together, sometimes over the sea, but more often in a series of wide circles round and about their home. They are masters of flight, and, after two or three flaps, will glide for long distances without an effort, alternately rising and sinking, varying their direction by a turn of the head or, as it seems, by presenting the broad surface of their wings to the different points of the compass, and sweeping either with or against the wind, apparently with equal ease. ”

“ In flight the wings are for the most part constantly quivered, with a quick and somewhat tremulous motion, but sometimes the bird will glide with them outstretched, and not moving, just over the ground, before it alights, or make a steep-down descent holding them set in this manner, and so settle. There is also a trick or mannerism of flight which is graceful, and may be of a nuptial character. Rising to a certain height on quivering wings, they sink down, holding them extended and motionless. ”

“ It is quite possible that birds can see the air itself by some arrangement of the lenses of their eyes which may either enable them to see the fine dust particles or to so polarise the light that the direction of its vibrations can be determined and the course of flight so changed that an air lane favourable to the path of the bird can be followed and by following out one stream lane among many, which has an upward trend sufficient to counteract the falling tendency, the bird can remain at an equal elevation. ”

“ This simple experiment shows that the various inclined surfaces requisite for flight are produced by the mere acts of extension and flexion in the dead bird. It is not, however, to be inferred from this circumstance that flight can be produced without voluntary movements any more than ordinary walking. The muscles, bones, ligaments, feathers, etc., are so adjusted with reference to each other that if the wing is moved at all, it must move in the proper direction—an arrangement which enables the bird to fly without thinking, just as we can walk without thinking. ”

“ It is necessary, therefore, at this stage to direct the attention of the reader somewhat fully to the subject of flight, as witnessed in the insect, bird and bat, a knowledge of natural flight preceding, and being in some sense indispensable to, a knowledge of artificial flight. The bodies of flying creatures are, as a rule, very strong, comparatively light and of an elongated form,—the bodies of birds being specially adapted for cleaving the air. ”

“ High authorities, and men who are expert aviators, tell us that the bird flies because it is able to pick out ascending air currents.
THEORIES ABOUT FLIGHT OF BIRDS.—Then we are offered the theory that the bird has an instinct which tells it just how to balance in the air when its wings are once set in motion. Frequently, what is taken for instinct, is something entirely different. ”

“ Flight is chiefly observed in the case of the birds of prey. The successful swoop of an eagle upon its prey, or the rapid determined flight of a hawk in pursuit of some other bird, is an encouragement to the observer (provided of course that the birds are seen on his right hand) to pursue untiringly any enterprise in which he is engaged, and is a promise of success and profit therein. In Scyros I once pointed out to my guide a large hawk chasing a flock of pigeons, which he at once hailed as a good omen and watched carefully as long as it was in sight ”

“ For, surely, there is a difficulty in explaining how the example of one vast body of birds, soaring forth on the morning flight, should not affect every individual of the still vaster body of which they form a part—the whole occupying, it must be remembered, a small and densely packed area—and why the impulse of the flying birds to fly should, apparently, become uncontrollable in each individual of them at the same instant of time. ”

“ They assist the bird in preserving its equilibrium. Without them the bird would be just as helpless in the air as a human being and could not remain afloat.
When the wind is still, or comparatively so, a bird, having secured the desired altitude by flight at an angle, may sail or soar with no wing action beyond an occasional stroke when it desires to advance. But, in a gusty, uncertain wind it must use its wings or alight somewhere. ”

“ They can also soar to some extent, rising higher and higher on outspread wings as they sweep round and round in irregular circles—like gulls, but far less perfectly, and they have to flap the wings more often. Add to this their downward-rushing swoops, their twists, turns, tumbles, zig-zaggings, and all manner of erratic aerial evolutions, and it must be conceded that the powers of flight which they possess are beyond those with which we generally associate them in our mind. ”

“ Between two seas the sea-bird's wing makes halt,
Wind-weary; while with lifting head he waits
For breath to reinspire him from the gates
That open still toward sunrise on the vault
High-domed of morning, and in flight's default
With spreading sense of spirit anticipates
What new sea now may lure beyond the straits
His wings exulting that her winds exalt
And fill them full as sails to seaward spread,
Fulfilled with fair speed's promise. ”

“ One of the most difficult, as well as most interesting, questions in bird-migration has been, How are birds guided in their flight? By instinct, has been the usual answer; but, thanks to the labors of such men as Cooke, Allen, Brewster, and Scott, the question is now better understood. Recent observations made at lighthouses and astronomical observatories go to show that many, if not most, of our smaller birds fly at very great heights while migrating—heights even as great as one to two miles. ”

“ Its flight is short and undulating, and is rarely extended to a greater distance than a quarter of a mile, as the bird frequently alights on a leafless branch, always flying a little below it and rising again just before it settles. ”