Wing coverts

“ It is necessary that the wings descend further than they ascend; that the wings be convex on their upper surfaces, and concave on their under ones; and that the concave or biting surfaces be brought more violently in contact with the air during the down stroke than the convex ones during the up stroke. The greater range of the wing below than above the body, and of the posterior margin below than above a given line, may be readily made out by watching the flight of the larger birds. It is well seen in the upward flight of the lark. ”

“ Above all, an untiring and swift wing is necessary, one that does not flag in the pursuit of game desperately putting forth its utmost efforts to escape, and one that is not baffled by the tortuous course of a moth driven to bay. A beak inordinately cleft and wings of extraordinary power—such, in a word, should be the equipment of the bird whose hunting ground is the vast expanse of the open air. ”

“ The Wing acts as an Elevator, Propeller, and Sustainer, both during extension and flexion.—The wing, as has been explained, is recovered or drawn off the wind principally by the contraction of the elastic ligaments extending between the joints, so that the pinion during flexion enjoys a certain degree of repose. The time occupied in recovering is not lost so long as the wing makes an angle with the horizon and the bird is in motion, it being a matter of indifference whether the wing acts on the air, or the air on the wing, so long as the body bearing the latter is under weigh ”

“ That birds which fly with flapping wings derive their support from the air, is undoubtedly true, and that the lift produced is due, not to the form, or shape, or area of the wing, is also beyond question. The records show that every conceivable type of outlined structure is used by nature; the material and texture of the wings themselves differ to such a degree that there is absolutely no similarity; some have concaved under surfaces, and others have not; some fly with rapidly beating wings, and others with slow and measured movements ”

“ That the wings invariably strike forwards during the down and up strokes in aerial flight is proved alike by observation and experiment. If any one watches a bird rising from the ground or the water, he cannot fail to perceive that the head and body are slightly tilted upwards, and that the wings are made to descend with great vigour in a downward and forward direction. The dead natural wing and a properly constructed artificial wing act in precisely the same way. ”

“ The wing is beautifully twisted upon itself, and when it is elevated and advanced, it rolls up from the side of the bird at varying degrees of obliquity, till it makes a right angle with the body, when it presents a narrow or cutting edge to the water. The wing when fully extended, as in ordinary flight, makes, on the contrary, an angle of something like 30° with the horizon. When the wing is depressed and carried backwards,58 the angles which its under surface make with the surface of the water are gradually increased. ”

“ An artificial wing, propelled and regulated by the forces recommended, is in some respects as completely under control as the wing of the insect, bat, or bird.
Necessity for supplying the Root of Artificial Wings with Elastic Structures in imitation of the Muscles and Elastic Ligaments of Flying Animals.—Borelli, Durckheim, and Marey, who advocate the perpendicular vibration of the wing, make no allowance, so far as I am aware, for the wing leaping forward in curves during the down and up strokes. ”

“ The upper surface of the wing is convex, the lower surface concave. In flying the wings are thrown forward and downward. Flying is not a flapping of the wings up and down, and if a bird were to strike its wings backward and downward, as its manner of flight is so often pictured, it would turn a forward somersault in the air. ”

“ The Wing at all times thoroughly under control.—The wing is moveable in all parts, and can be wielded intelligently even to its extremity; a circumstance which enables the insect, bat, and bird to rise upon the air and tread it as a master—to subjugate it in fact. The wing, no doubt, abstracts an upward and onward recoil from the air, but in doing this it exercises a selective and controlling power; it seizes one current, evades another, and creates a third; it feels and paws the air as a quadruped would feel and paw a treacherous yielding surface. ”

“ In birds which glide or skim, it has appeared to me that the wing is recovered much more quickly, and the down stroke delivered more slowly, than in ordinary flight—in fact, that the rapidity with which the wing acts in an upward and downward direction is, in some instances, reversed; and this is what we should naturally expect when we recollect that in gliding, the wings require to be, for the most part, in the expanded condition. ”

“ Their plumage is of the finest order, copious, and without the slightest stain. They find great difficulty in getting on wing, and must run twenty or thirty yards along the ground with expanded wings, before they can get fairly under way. ”

“ Now, although the wings do, certainly, more or less wag the body up and down, nevertheless the body is the axis of the mill-wheel of which the wing-borders are the floats, so that even if the bird tried for the body, unless the attack came exactly from behind, the flapping wings would tend to protect it by constantly getting in the way of the bird's beak, but this would be at the expense of these delicate fabrics, which would smash themselves against it. ”

“ To meet this difficulty, the wing is so shaped that it is concave or hollow upon its lower surface, so that it gathers the air together and prevents it from escaping; while the upper surface is convex or bulging, so that the air slides off from it when the wing is moved upward. ”

“ Hence the whole mass of the bird rebounds, making a fresh leap through the air; whence it follows that flight is simply a motion composed of successive leaps accomplished through the air. And I remark that a wing can easily beat the air in a direction almost perpendicular to its plane surface, although only a single one of the corners of the humerus bone is attached to the scapula, the whole extent of its base remaining free and loose, while the greater transverse feathers are joined to the lateral skin of the thorax. ”

“ In all the wings which I have examined, whether in the insect, bat, or bird, the wing is recovered, flexed, or drawn towards the body by the action of elastic ligaments, these structures, by their mere contraction, causing the wing, when fully extended and presenting its maximum of surface, to resume its position of rest and plane of least resistance. ”

“ As he rises vertically, forcing his way in a straight line upwards, his wings almost meet above his back and again beneath the body; they are put forth to his full stroke. When his flight inclines and becomes gradually horizontal, the effort is less and the wing tips do not approach so closely. ”

“ THE DOWNWARD BEAT.—It is argued that the downward beat of the wings is so much more rapid than the upward motion, that it gets an action on the air so as to force the body upwardly. This is disposed of by the wing motion of many birds, notoriously the crow, whose lazily-flapping wings can be readily followed by the eye, and the difference in movement, if any, is not perceptible. ”

“ The wing would have much less purchase on fig. 8 than on fig. 9, provided the surfaces exposed by the latter were passive or dead surfaces. But they are not dead surfaces: they represent the spaces occupied by the rapidly vibrating wings, which are actively moving flying organs. As, moreover, the wings travel at a much higher speed than any wind that blows, they are superior to and control the wind; they enable the insect to dart through the wind in whatever direction it pleases. ”

“ The curves and the reversal thereof are necessary to give continuity of motion to the wing during its vibrations, and what is not less important, to enable the wing alternately to seize and dismiss the air.
70 In birds which skim, sail, or glide, the pinion is greatly elongated or ribbon-shaped, and the weight of the body is made to operate upon the inclined planes formed by the wings, in such a manner that the bird when it has once got fairly under weigh, is in a measure self-supporting. ”

“ In tying it to the running string between the two sticks, it is necessary so to arrange as not to impede the wing movement and not to turn over the bird in flipping it upwards. It is not the rise that must be looked to for attracting wild ones, but the natural way the bird settles after it has been flipped into the air. ”

“ Curves in the Wing of a Partridge in Flight.
The wings, when flexed and extended in flight, assume curved surfaces, which change at each instant and carve the air, as does the tail of the fish the water, into complex wave-lines; and such is the structure of the wing that these results are inevitable when it is put in motion. "The muscles, bones, ligaments, and feathers, are so adjusted with reference to each other that, if the wing is moved at all, it must move in the proper direction." The bird no more thinks of its motions in flying than we do of ours in walking ”

“ They afford an opportunity only of admiring at a distance the extraordinary agility and the stateliness likewise of their motions, the richness of their plumage, and the great propriety there was of ascribing to them ‘an expanded, quivering wing.’ Nothing certainly can be more beautiful and entertaining than such a sight! the wings, by their repeated though unwearied vibrations, equally serving them for sails and oars; while their feet, no less assisting in conveying them out of sight, are no less insensible of fatigue. ”

“ Some of their wings are neatly cut to an edge and bordered; of some the edge is lost in colour, because no line is drawn along it. Some seem to have ragged edges naturally, and look as if they had been battered. Towards the end of their lives little bits of the wing drop out, as if punched. The markings on the under wings have a tendency to run into arches, one arch above the other. The tendency to curve may be traced everywhere in things as wide apart as a flower-bird's wing and the lines on a scallop-shell. ”

“ How to apply Artificial Wings to the Air.—Borelli, Durckheim, Marey, and all the writers with whom I am acquainted, assert that the wing should be made to vibrate vertically. I believe that if the wing be in one piece it should be made to vibrate obliquely and more or less horizontally. ”

“ The wing is not one surface but a series of narrow surfaces lapping in such a manner that they unite to form one broad surface when the downward stroke is made, and with the upward stroke are separated so that the air passes between them. Greater power in the downward stroke and less resistance in the upward stroke are also secured by the curvature of the wing. ”

“ Before taking their spring they run some paces, raise themselves a little at first, and then unfold a powerful and rapid wing. In the air they form very nearly an isosceles triangle, possibly for the purpose of cutting the element with greater facility. When attacked by an eagle, or the wind is likely to break their order, they close in circles. ”

“ All wings obtain their leverage by presenting oblique surfaces to the air, the degree of obliquity gradually increasing in a direction from behind, forwards and downwards, during extension when the sudden or effective stroke is being given, and gradually decreasing in an opposite direction during flexion, or when the wing is being more slowly recovered preparatory to making a second stroke. ”

“ The flexion of the wing is most obvious when the bird is exerting itself, and may be detected in birds which skim or glide when they are rising, or when they are vigorously flapping their wings to secure the impetus necessary to the gliding movement. ”

“ Flexion of the Wing necessary to the Flight of Birds.—Considerable diversity of opinion exists as to whether birds do or do not flex their wings in flight. The discrepancy is owing to the great difficulty experienced in analysing animal movements, particularly when, as in the case of the wings, they are consecutive and rapid. My own opinion is, that the wings are flexed in flight, but that all wings are not flexed to the same extent, and that what holds true of one wing does not necessarily hold true of another. ”