. The structure and life of birds . upstroke there is a further turn, and itmoves edgeways This description of themovements of the wing refers to very vigorous flight,such as we most commonly see when the bird isgetting up steam. When he has plenty of way onthere is no need for him to take these very long andexhausting strokes, unless, like the Duck, he is oneof those that seem always to fly with effort. In birdsof long flight, the wing does not rise very high ordescend very low, and it is flexed very little, if at all,when it is raised. These points can be made out if aGull is watch
. The structure and life of birds . upstroke there is a further turn, and itmoves edgeways This description of themovements of the wing refers to very vigorous flight,such as we most commonly see when the bird isgetting up steam. When he has plenty of way onthere is no need for him to take these very long andexhausting strokes, unless, like the Duck, he is oneof those that seem always to fly with effort. In birdsof long flight, the wing does not rise very high ordescend very low, and it is flexed very little, if at all,when it is raised. These points can be made out if aGull is watched when it is flying steadily. In some of1 Further details under next heading. VII FLIGHT 221 Messrs. Wyless photographs of Gulls, flying horizon-tally at some height from the sea, there is not a singleone among the large number that has its wings flexed.(See frontispiece.) Figures described by different parts of the Wing. If you take an insect (a Bluebottle, for instance, or aDrone) and hold it down, the wing tips as they vibrate. Fig. to (after Marey). Figure described by tip of Crows The backward movement neary? is largely due to the flexing, the forward movement near st to the straightening of the wing. will be seen to describe a figure of 8. If the sunlightbe made to fall upon them, it will be all the have tried painting the tips with body white, butthe rapid vibration soon dislodges the paint. It ismuch harder to discover the trajectory of a birdswing. Professor Pettigrew has strongly insisted thatit is an 8 as in the case of insects, but the lower circle 1 I have corrected the mistake by which the words rightand left have been accidentally transposed in ProfessorMareys explanation of the figure. 222 THE STRUCTURE AND LIFE OF BIRDS chap. of the 8 either does not exist, or at any rate is reducedto very small dimensions. Applying machinery tothe birds wing, Professor Marey succeeded in tracingthe figure described by the outer end of the is an ell
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