Flight (biology)

“ To tread upon the air (and this is what is really meant) is, at first sight, in the highest degree utopian; and yet there are thousands of living creatures which actually accomplish this feat. These creatures, however varied in form and structure, all fly according to one and the same principle; and this is a significant fact, as it tends to show that the air must be attacked in a particular way to ensure flight. It behoves us then at the outset to scrutinize very carefully the general configuration of flying animals, and in particular the size, shape and movements of their flying organs. ”

“ The true movements of flight, so made familiar to our brain, may in part be detected afterwards by the naked eye. Yet the speed and direction of birds’ flight in air, and the necessary distance between them and ourselves, which every beat makes greater, must always leave it something of a mystery. But the change of medium from air to water gives an added charm to flight. ”

“ 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. ”

“ THE COMMON FLY.—So many birds have been cited in support of the various flying theories that the house fly, as an example has been disregarded. We are prone to overlook the small insect, but it is, nevertheless, a sample which is just as potent to show the efficiency of wing surface as the condor or the vulture.
The fly has greater mobility than any other flying creature. By the combined action of its legs and wings it can spring eighteen inches in the tenth of a second; and when in flight can change its course instantaneously. ”

“ For we know from our modern birds that the power of flight may be to some extent gauged from the degree of development of the keel, which is simply a great ridge for the better insertion of the muscles of flight. ”

“ We all notice the first swallow almost as soon as the first cuckoo; for though the one bird’s note catches the ear, the flight of the other arrests the eye as certainly. And what a flight it is! Has it ever been computed how many hundred miles it flies every day? For hours they are on the wing, flying at the rate of a mile a minute, and always with exquisite grace. ”

“ And careful observations have placed beyond question the fact that flight is also instinctive. A swallow, for example, taken from the nest under conditions which made it practically certain that it had never yet taken wing, exhibited guided flight, and attempted to alight on a suitable ledge. Of course flight is generally a deferred instinct, and is not performed until the wings have reached a suitable state of development. ”

“ The organs of flight are developed in a very high degree. Almost the whole life of these birds is passed in the air; from earliest "morn to dewy eve," we see them careering along in their rushing flight, and, as has been truly observed, they "dash along apparently as untired when evening closes, as when they began their aerial evolutions with the first dawn of day." ”

“ Of all animal movements, flight is indisputably the finest. It may be regarded as the poetry of motion. The fact that a creature as heavy, bulk for bulk, as many solid substances, can by the unaided movements of its wings urge itself through the air with a speed little short of a cannon-ball, fills the mind with wonder. Flight (if I may be allowed the expression) is a more unstable movement than that of walking and swimming; the instability increasing as the medium to be traversed becomes less dense. ”

“ 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. ”

“ They are all good fliers, and some, from the extreme expanse of their wings, have extraordinary powers of flight. They spend a great deal of time upon the wing, some soaring far out over the ocean, or mounting to a most sublime elevation, others beating over a limited space, till the appearance of a fish beneath them arrests their attention, when they plunge down upon it, and instantly rise again into the air. ”

“ Flying is the best state of all. Even the humans do their poor [Pg 203] best to fly. Every part of me is modified for flight. My knees bend the wrong way so as to better stretch my wing-membranes. My tail serves as a rudder, and in the hollow pouch about it I can trap a beetle, ay, and carry him where I will. My sense of touch is the most delicate in all the world. I never dash myself, like blundering bird, against a wire. If you would know the secret, look at the trembling bristles on my muzzle, look at the earlets within my ears, look at the sensitive wing-membrane between my fingers. ”

“ 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 ”

“ Finally, when the wing has reached the lowest point of its depression, it is not over the mass of air which it has just set in motion, because the motion of translation of the bird continually brings it into regions where the air is at rest. All of these conditions are evidently favorable to flight, since they increase the resistance of the air, which alone furnishes to the bird its support, and the reaction to its moving wing. ”

“ The flight of a bird is a wonderful thing, my boy. He spreads those frail wings of his, and launches into the air, up, up, above trees and steeples, then on and on, being able to fly several hundred miles without resting. Some birds, when the wind aids them, cover more than a hundred miles in a single hour. ”

“ Many unscientific observers of the flight of birds have imagined that a wind or a horizontal movement of the air is all that is necessary to sustain the weight of a bird in the air after the manner of a kite. ”

“ It captures its food, eats and drinks while on the wing, and some one has said that he often wondered if it did not, at times, even sleep while flying. Its wonderful endurance and power of flight have more than once taken it across the ocean, where it has happily surprised the ornithologists of Europe. ”

“ When we take into consideration how entirely aerial is their life, and the prodigious relative force requisite to enable them to keep suspended in the air during the entire day, almost incessantly, either in rapid motion or accomplishing the most violent vibrations, we can but be amazed at the extraordinary powers of flight and endurance they manifest. ”

“ Even in this day of scientific research and astuteness, it must not be supposed that everything about the mechanics of avicular flight is understood. We may readily comprehend how a bird, without fluttering its wings, can poise in the air ”

“ If we compare air with water we find it is nearly 1000 times lighter. To meet these peculiarities the insect, bird and bat are furnished with extensive flying surfaces in the shape of wings, which they apply with singular velocity and power to the air, as levers of the third order. In this form of lever the power is applied between the fulcrum and the weight to be raised. The power is represented by the wing, the fulcrum by the air, and the weight by the body of the flying animal. ”

“ They take flight very suddenly, bursting into a thousand chirping, scolding notes, pursue each other through the air, and, after wheeling about the field for a minute or two, suddenly drop down into the grass again and are silent as before. ”

“ The fact is that there is no unique design for flight; given the power and its right use, almost anything can fly. If the sea-gull can fly, so can the duck, with a much heavier body and a much less proportion of wing. The moth can fly ”

“ In the case of birds such as those above cited, the soaring mode of flight is so extensively employed that without doubt the process of natural selection, or whatever other method Nature may employ, may be relied upon to have approximated the proportions of least resistance proper to the ordinary velocity of flight of the species. ”

“ In the case of smaller birds or insects, such as the dragon-fly cited, it is an open question to what extent the problem is modified by the exigencies of active flight, and so the evidence, as confirming or otherwise the present theory, is at the best inconclusive. ”

“ 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. ”

“ Here I have only touched upon the speed and power of flight, but the whole subject is one of the most fascinating branches of natural history. No reference has been made to the marvellous movements of birds in the air, which constitute the very poetry of motion—the stationary balancing, hovering, circling, and gliding, all of which may be observed, especially among our own birds of prey. ”

“ That walking, swimming, and flying represent integral parts of the same problem is proved by the fact that most quadrupeds swim as well as walk, and some even fly; while many marine animals walk as well as swim, and birds and insects walk, swim, and fly indiscriminately. When the land animals, properly so called, are in the habit of taking to the water or the air; or the inhabitants of the water are constantly taking to the land or the air; or the insects and birds which are more peculiarly organized for flight, spend much of their time on the land and in the water ”

“ I believe the power of flight is used chiefly, if not exclusively, as a means of escape from danger. The bird rises up when almost trodden upon, rushing into the air with a noise and violence that fill one with astonishment. It continues to rise at a decreasing angle for fifty or sixty yards, then gradually nears the earth, till, when it has got to a distance of two or three hundred yards, the violent action of the wing ceases, and the bird glides along close to the earth for some distance, and either drops down or renews its flight. ”

“ Those apparent inconsistencies in the dimensions of the body and wings are readily explained by the greater muscular development of the heavy-bodied, small-winged insects, birds and bats, and the increased power and rapidity with which the wings in them are made to oscillate. This is of the utmost importance in the science of aviation, as showing that flight may be attained by a heavy powerful animal with comparatively small wings, as well as by a lighter one with greatly enlarged wings. ”

“ How Balancing is effected in Flight, the Sound produced by the Wing, etc.—The manner in which insects, bats, and birds balance themselves in the air has hitherto, and with reason, been regarded a mystery, for it is difficult to understand how they maintain their equilibrium when the wings are beneath their bodies. ”

“ 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. ”

“ The transition from swimming to progression in the air is natural and easy. The method by which the flying-fish rises from the water is similar to that of the albatross, that prince of flying-birds, and, indeed, to perhaps all other birds, when in the act of taking flight upon the water. Momentum is obtained by rushing forward with both feet and wings. ”

“ They arrive often one by one and "seem to drop literally from the clouds," but when they actually departed it was easy to see their method. They "fly upwards and onwards, then they hesitate, fly sideways once or twice, again attempt an upward and onward flight, hesitate again, and down they come once more to earth." ”

“ The organs which support animals in the air are thus seen to be more or less dissimilar in each of the great groups of animals. They fall into three chief types: first, the parachute; secondly, the wing due to the feathers appended to the skin; and thirdly, the wing formed of membrane, supported by enormous elongation of the small bones of the back of the hand and fingers. The two types of true wings are limited to birds and bats; and no living reptile approximates to developing such an organ of flight as a wing. ”

“ Air-cells in Insects and Birds not necessary to Flight.—The boasted levity of insects, bats, and birds, concerning which so much has been written by authors in their attempts to explain flight, is delusive in the highest degree. ”