Birds in Flight

by W. P. Pycraft

Sketches of Ducks in flight 1922

1. 1a.		Scaup.
2.		Goldeneye.
3. 4.		Pochard.
5. to 10.		Mallard.

Whether the legs are carried drawn close up beneath the breast, or thrust backwards under the tail, the purpose of this disposal is the same—to prevent any interference with the “stream-lines” of the body which would impede flight.

On the matter of the speed of flight there seems to be much misconception. Gätke, the German ornithologist, gravely asserted that the little Arctic blue-throat—one of our rarer British birds—could leave its winter resort in Africa in the dusk of evening, and arrive at Heligoland—where he spent so many years studying bird migration—nine hours later. That is to say it could travel 1,600 geographical miles in a single night, at the astounding velocity of 180 miles an hour! According to another estimate of his, curlews, godwits, and plovers crossed from Heligoland to the oyster-beds lying to the eastward, a known distance of rather more than four English miles, in one minute; or at the rate of over 240 miles an hour. Against such extravagant estimates it is hardly necessary to bring rebutting evidence. But if any be demanded it may be furnished by the carrier pigeon, which has been known to maintain a speed of 55 miles an hour for four hours in succession: and it is extremely unlikely that this is much, if at all, exceeded by any wild bird during long-distance flights.

That our spring and autumn migrants must possess wonderful powers of endurance is beyond question. And it is equally certain that thousands must perish by the way. By this means is the standard of flight maintained—the weak perish. Even the minimum standard of efficiency for the survival of such an ordeal must be a high one.

Few of us see anything of these marvellous migration flights. For, in the first place, they are generally performed at night, and at a great height, often beyond the range of human vision. Only as they approach land, and their destination, do they descend. American naturalists have made some interesting observations by directing a telescope against the sky. Thus, Mr. Frank Chapman, by turning his instrument towards the full moon, has seen birds passing at night at an altitude, according to his computation, of five miles: while the late Mr. W. E. D. Scott saw, through an astronomical telescope at Princeton, New Jersey, great numbers of birds passing across the face of the moon—warblers, finches, and woodpeckers among them. Mr. Chapman again, on another occasion, saw no less than 262 birds pass over the field of his telescope at a height of from 1,500 to 15,000 feet: and the most remarkable thing of all was the fact that the lowest birds were flying upwards, as if they had risen from the immediate neighbourhood and were seeking the proper elevation to continue their flight.

As has already been remarked, when nearing their destination migrating birds descend, though still many miles from land. Should a gale be raging they fly so low that they barely top the waves. And this, apparently, to escape, so far as is possible, the force of the wind. Larks, starlings, thrushes, and other small birds, can sometimes be seen during daylight crossing the North Sea in their thousands. At such times many will often afford themselves a brief rest in the rigging of ships, homeward bound, but the main host hurry on. The beautiful golden crested wren, our smallest British migrant, is one of these. A glance at our charming coloured plate will show at once that the wing is not that of a bird of strong flight. There is no more interesting experience to the bird-lover than that of watching the tired travellers drop earthwards, as they leave the dreadful sea behind them.

With all birds yet retaining the power of flight there is always a liberal “margin of safety” in regard to the wing area. That is to say this is always in excess of the minimum area necessary to make flight possible. This much, indeed, is manifest from the fact that the eagle can bear off a victim equalling himself in weight. Should he miscalculate, he can always drop his burden, or lessen its weight by eating part of it on the spot. Not so the osprey, or the sea-eagle, which have been known to plunge down and drive their talons into fishes too large to be raised. Unable to release their grip, death, by drowning, has inevitably followed.