Birds' Methods of Steering
THE flight of birds still presents several unsolved problems. How they steer, has never been fully explained. With the naked eye or, still better, with a field glass, many of them can be seen to use their tails, lowering the left or right side according to the direction in which they wish to go. Thi...
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Veröffentlicht in: | Nature (London) 1893-07, Vol.48 (1239), p.293-294 |
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Sprache: | eng |
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Zusammenfassung: | THE flight of birds still presents several unsolved problems. How they steer, has never been fully explained. With the naked eye or, still better, with a field glass, many of them can be seen to use their tails, lowering the left or right side according to the direction in which they wish to go. This use of the tail as a rudder is much practised by pigeons, jackdaws, rooks, larks, swallows, housemartins, sandmartins, and I believe, by most of our common birds. Gulls let down a foot on one side or the other, and, no doubt, many other web-footed birds do the same. Still a rook or pigeon that has lost his tail manages to steer well, the chief result of the loss being that he cannot stop suddenly, nor float upon the air, but must take rapid strokes with his wings. What other method, then, has the bird of steering? One fact that bears upon this question can be easily observed. When a bird wishes to turn to the left he moves the centre of gravity of his body and flings himself on his left side, the right wing pointing upward and the left downward. How does he throw himself into this position? Most writers say that it is by striking harder with one wing than the other. In turning to the left the right wing would give a vigorous stroke, and so raise the right side of the body more than the left. At first sight it seems as if this explanation could not be the true one, since after a hard stroke the right wing should be lower than the left, which has only given a gentle one, and yet it is the right wing that is raised. But we must not be too hasty in drawing conclusions from this. When the down stroke takes place the wings do not descend far; the body rises so that the end of the wing appears to have described a much greater arc than it has done in reality. If, then, with the right wing a much harder stroke is given than with the left, the right side of the body will at once be raised, and the whole bird will be thrown upon its left side, while the movement of the wing itself may not be enough to be perceptible. If birds are watched as they fly, one wing seems always to be at the same angle to the body as the other, so that a straight line connecting the tips of the wings would pass through the two shoulder joints, or be parallel to a line passing through them. Instantaneous photographs of birds on the wing seem to me to bear this out. One wing may point up and the other down, but that is through the swaying of the whole body to one side or the other. In spite of th |
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ISSN: | 0028-0836 1476-4687 |
DOI: | 10.1038/048293b0 |