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FIG. 1. SUCCESSIVE MOVEMENTS OF A GULL, MADE BY AN OBSERVER FOLLOWING
THE LINE OF ITS FLIGHT.
TRANSLATED FROM LA NATURE
MRS. F. M. C. HOLLEY
MONG the unexplained things of The sparrow gives the impression of a
nature that man has been living force which raises itself quickly fretting his brain over to little and Alies with rapid beatings of the wings purpose as yet, is the fact that to traverse only a few yards or to raise
some birds have the power to itself to a slight elevation. The pigeon holds themselves in the air without being rises with the same facility, but its beatdependent upon the beating of their ings are less rapid and are produced with wings. Direct observation of birds and much more regularity; its flight, more the character of their flight has estab- ample than that of the sparrow, gives the lished the fact that birds of a certain impression that it belongs to a more size do not fly exclusively by beating powerful bird, capable of sustaining its their wings; they soar in the air. It may course a longer time. be said that this kind of movement is But a new element appears in the general with birds above the weight of pigeon's flight—the facility, of which it four and one-half pounds, as if nature frequently makes use, of suspending the had not known how to enable large birds beating of its wings in order to glide to use the same kind of flight as small through the air. In ordinary weather ones.
with a moderate wind it holds itself thus How, under these conditions can we when from a high point it wishes to hope that man, surpassing nature, should descend to the earth; it half folds back be able to make a beating of wings that its wings and lets itself fall in a concave will lift not merely four and one-half curve which may become ascending. This pounds but his own weight?
practice is frequently followed by swalWorks on the flight of birds, under- lows, swifts and hawks, which use the taken during the past few years are very momentum gained during the fall in numerous, and it is becoming difficult to order to mount again. During this fall find one's way amidst the contradictions, and this automatic ascension, there is no uncertainties and obscurities which one expenditure of force necessary on the meets. However a certain number of part of the bird, which benefits by this facts have within this time been ascer- rest in order longer to continue its flight. tained by the experimental method which It is in this way that swallows succeed in have often been corroborated by careful ploughing through the air, almost withcalculations,
out stopping, from morning until evening.
The kite, the sparrow and the buzzard the wind for their movement. Simple practice the kind of fight called the observation permits us to establish among sailing Aight, but the true kings of the birds some clearly defined classes: air are the eagles, the vultures and the First, birds exclusively rowers; second, condors which travel through space with- birds practicing the rowing flight and out a single beating of the wings like soaring flight; third, birds practicing living aeroplanes, capable even of re- rowing and sailing; fourth, birds pracmaining immovable, as though fastened ticing only sailing fight. in the sky.
Are these distinctions, which are Even superficial observation enables based only on the different variety of one to ascertain that the same bird may methods for accomplishing the action of have different modes of fight and that flying, dependent upon the construction the different species fly in different ways. of the wing, and are there found in the
Two kinds of flying are in fact ad- wings of a bird such modifications that mitted; that obtained exclusively by the we may without hesitation attribute to beating of the wings, the flight by row them the special character of the flight? ing, as it may be called, and the soaring Observers have always replied in the flight, during which the bird keeps its affirmative, after having proved that the wings extended in the course of its form of the wings is essentially variable progress through the air. There are two and adapted to the kind of flying; but it different modes of soaring flight; soaring is modern research which has scienflight properly so called, which is only tifically established this dependence. .
There exist two well defined types of wings among which, evidently, all the gradations are observed, but the distinction is easy. It is sufficient indeed, to glance at the two figures five and six in order to discover that the hawk's wing is stretched to a point, while the eagle's is rounded. This is due to the length of the quili feathers which diminishes from the first one to the last in
temporary and accessory to rowing flight, and sailing flight, which is the normal mode of locomotion for large birds capable of remaining entire days in the air by
The point of the wing carried forward.
the hawk's wing, while in the eagle's have a more ample Aight, possess narwing the longest feather is the sixth. rower wings which, in addition, facilitate Besides, the rowing wing is homogeneous their veerings. The wing stretches in on its posterior side, whilst the sailing proportion as the bird, from being a wing is jagged. This last peculiarity is rower, becomes a sailer. But here again due to the special conformation of the one finds some broad and some narrow primary feathers which, instead of pre- wings. The latter, provided for work senting the form of
in violent winds, a knife as do the
belong to sea birds, rowing feathers,
such as the petrel become narrow at
and frigate birds; the middle of their
the others have length while the
been given to the quill loses some of
great birds of prey its rigidity. There
in order that they results a certain
may take advansuppleness of the
tage of the least edge of the sailing
breath of wind wing which, during Fig. 4. APPEARANCE OF A Bird That Soars Slowly. and may cover flight, becomes con
enough space to vex and appears in
find their prey. dented by reason of the divergence and Now, how does the bird use its wings the bending of the feathers. This atti- in order to keep itself up and to proceed tude is striking in figure ten, and it is pre- through the air ? Flying always comcisely this lack of rigidity which renders prises three phases or periods; the desailing birds unfit for rowing flight. parture, the flight, properly so called, and
Besides these characteristics, based for lastly the alighting. We are going to the most part on the structure of the study these three phases in each one of wing, one may again examine the rela- the groups of birds that we have detion of the two dimensions, length and scribed: rowers, half sailers, and sailbreadth. According to the French Mou- ers. illard, who was one of the most careful The average species of small size, beobservers, the rowers all have short longing to the rowing group, take their
wings but the start after a hop
Fig. 6. THE SAILING WING pigeon, which bodies vertically so *
Fig.'5. THE ROWING WING
OF A FALCON,
OF AN EAGLE.
as to permit at the first a flapping of wings. When these birds rest on an elevated support, it is sufficient for them to let themselves fall in order to acquire the start or indispensable spring for the action of the wings.
The necessary effort for Aight is considerable, but it diminishes rapidly in proportion as the speed of the bird approaches the normal condition. One gains an understanding of this by
Fig. 7. THE FRIGATE Bird-ONE OF THE STRONGEST OF FLYERS. appreciating the speed and amplitude of the flapping of the wings; in the sea gull the amplitude components—the vertical and the horiattains one hundred to one hundred and zontal; the first serving to raise the wing ten degrees at the departure and lowers and the other, directed with a contrary from thirty degrees to forty degrees in motion, consequently slackens the speed normal flying; in the partridge the ex- of the bird. When to the relative wind penditure of force is so depressing that there is added the absolute wind,—that the little cries that this bird makes at the is, when the bird fies against the wind, moment of its flight are attributed to the result is still more defined, and this fatigue.
explains why many rowing birds try During the fight the raising of the always to take their flight with the beak wing is obtained only by the action of toward the wind. the middle pectoral muscle which has no All authors are agreed in defining other function and acts intermittently; soaring as a word which signifies that but this would be insufficient if nature kind of flight which a bird executes withdid not aid by an artifice to reduce the out flapping the wings, and with the resistance of the air to its lowest value. wings more or less extended. Soaring It has been discovered, in short, that, thus understood comprises two different during the first flappings, the wings are forms: soaring flight properly so called, like the slats of open Venetian blinds. for which the bird utilizes the speed The feathers meet the air edgewise. acquired during a course of beating the This arrangement, which offers a mini- wings or by a fall from an elevated point, mum of resistance to the passage through and sailing flight, in which the bird has the air, is caused by an automatic pivot essential need of the assistance of the ing of the feathers, due to a very com- wind. plicated disposition of their elastic liga- The bird that soars may be compared ments. In proportion as the bird gains to a kite that one draws behind him speed the raising of the wing is caused while running and which rises and by an increasingly weaker action of the keeps itself up if the air is calm. All the middle pectoral muscle, and it becomes rowers of medium size, herons, storks, entirely passive
buzzards, sea gulls when the motion is
and hawks, practice normal. It is in
this kind of flying, deed, the relative
and it is always wind produced by
easy to observe the the speed of the
periods during bird which acts on
which they suspend the convex face of
the flapping of their the wing. Here Fig. 8. APPEARANCE OF A Bird THAT GLIDES
wings, and continue
RAPIDLY. again we find two
The point of the wing is carried backward, their course, hold
possible from an elevated starting point, it is necessary to fall one yard in order to traverse eight yards. A bird which would soar to the height of 1,000 yards would thus be able to land without fatigue at a distance of 8,000 yards.
Among soaring birds the sustaining qualities commence to gain on the propelling qualities; the concavity of the wing becom
ing no longer necessary Fig. 9. THE STORK IN Soaring Flight.
except at the moment of the
flappings, is assured only ing their wings extended almost without by the elasticity of the last quill feathers losing any speed; then a few vigorous opposed to the rigidity of the first; bestrokes of the wings will quickly start sides, the surface of the wing is reduced them again on their way. Such flying is and the tip gains a considerable developa gliding over the air, and the great forcement. Thus there is produced a narrow acquired during the period of the beating wing with a convex edge which is at of the wings is utilized by the bird for once an excellent organ of propulsion taking support on the air and for con and a very good soarer, qualities indistinuing its course either while rising, pensable for assuring to these birds their remaining at the same height, or de- busy existence in the pursuit of very scending. According as its passage fol- fugutive prey. lows the one or the other of these direc- Clearly then this condition, pushed to tions the speed diminishes rapidly, the extreme, will lead to flight by sailing, slowly, or increases. The bird which practiced only by birds which are no presents most frequently these different longed rowers and which borrow the modes of flying is the falcon in hunting necessary energy for their movement When from a great height it perceives from another source than their muscles. its prey, it lets itself fall almost vertically Among the large sailing birds only the in such a manner as to return and attack sustaining qualities exist; no more conits victim from beneath ; if it fails, it sets cavity of the wing, no more convexity or its wings and its body with the purpose predominance of the tip, but large flat of utilizing the enormous force acquired wings provided with extremely supple during the fall to mount again to a feathers with slight spread of the tip. height when it commences again this The form of the wing itself is modified; manoeuvre and continues these duckings, the enlargement of the surface is obwithout interruption, and consequently tained not by increasing the span, which without fatigue, until the prey is cap- would be inconvenient for the start, but tured.
by filling up the angle at the end of the The pigeon also offers us frequent ex- wing which from being pointed becomes amples of soaring. When, perched on a rectangular. roof, it wishes to descend to the ground. These are actual observations, and it lets itself fall vertically then, reducing although denied by authors who have its speed by flapping its wings or, if it never witnessed this kind of flying, Aight has some space before it, it lets itself by sailing, are today definitely admitted, glide following a parabolic curve which and no longer does any one deny that, places it gently on the ground.
in the large bird, the propelling and susBy observation of different soaring taining powers are obtained, simply by birds and by experiments performed with the reaction of the air in motion, by the soaring machines it has been shown that, wind alone. The agreement ceases when for the bird wishing to land as far as there is a question of explaining the