462 



THE BIRDS 



hour, with the help of the wind. Racing pigeons can average 40 miles 

 an hour or more for considerable periods. Air speeds of 30-50 m.p.h. 

 can certainly be reached by many birds: swifts are said to reach 100 

 m.p.h. in still air. 



Fig. 275. Pigeons (Columba), photographed during take-off, with exposures of 

 1/825 second. A, front, and b, rear view, with wings together, c, nearly, and d, 

 quite at bottom of downstroke; note pronation and forward movement of wing. 

 E and F, wings during the upstroke; in f the primary feathers have opened; note 

 that the wing moves backwards and that the motion is faster than on the down- 

 stroke. (From photographs by Aymar.) 



19. Take-off and landing 



At the take-off the bird has to acquire sufficient forward momentum 

 to provide lift, and yet must leave the air sufficiently undisturbed for 

 subsequent beats to be effective. In many birds, especially the smaller, 

 the jump provided by the legs is adequate for the take-off (Fig. 274). 

 Large birds must run or swim rapidly to obtain sufficient speed. Eagles 

 are said to be unable to rise without a long run, and many large birds 

 nest on a cliff or tree, which gives them an up-current for the take-off. 

 Swifts usually come to rest high up and can only rise off the ground 

 with difficulty. The albatross is unable to take off from the sea surface 

 in a dead calm. 



The first beats are usually very large, beginning with the wings 

 above the back and held at such an angle as to produce a large forward 



