98 THE FLIGHT OF BIRDS 



comparatively big birds the Grouse and the Partridge. 

 The great concavities beneath their wings, no doubt, 

 aid them much. But the intervals of gliding, 

 depending as they do on the preliminary attainment 

 of great momentum, necessarily come at rarer 

 intervals than they do in the case of the small bird. 

 I am not speaking here of the long glides achieved 

 without loss of altitude by some large, or fairly large, 

 birds when the wind has an upward trend. That is 

 a feat of the same nature as soaring, and I reserve 

 it for another chapter. 



In another way the big and the small bird present 

 a striking contrast. The former is often the slave 

 of his own momentum, and only with difficulty and 

 effort deviates from his line of advance ; the Goose 

 and the Duck are good examples of this. The 

 Swallow, on the other hand, turns with the utmost 

 agility and ease. Some bigger birds have a wonder- 

 ful nimbleness, though, in this respect, I think, they 

 are no match for the Swallow. The Sparrow-Hawk, 

 as he pursues some coveted small bird, turns and 

 twists among the trees and bushes with great skill, 

 his long, broad tail helping him very much in steering. 

 Birds of prey must, of course, have great nimbleness, 

 great power of suddenly checking themselves or sud- 

 denly changing their course ; otherwise they would 

 be unsuccessful as hunters, and would dash themselves 

 to pieces when swooping upon some intended victim 

 that was flying not far above the ground or a tree. 

 The Lapwing turns to account his power of putting 

 on the brake and making sudden turns by dashing 

 at his enemy, alarming him, then suddenly pulling 

 up and retreating only to make another dash. The 



