THE BIRD IN THE AIR. 89 



into a more or less vertical position, according to the angle at 

 which he wants to ascend; if he wishes to glide down, he just 

 lets himself fall forward. The straighter the body is held the 

 straighter up the bird goes. The straighter it is held the more 

 directly he descends. 



If you should ever see a game bird " tower " you will notice 

 how erect the body is. I know no flight among our American 

 birds so nearly vertical as the towering of the ruffed grouse, 

 but it is an exhibition not often seen unless one is with a gun- 

 ner, as the birds seldom or never tower unless wounded in the 

 head. 



We have already described the forward movement of the 

 bird in studying the stroke. Let us notice again the peculiar 

 folding of the upraised wing and the rolling secondaries which 

 spill the air and make the work of lifting the wing both quick 

 and easy. 



Speed in flight is attained in two ways by the shape of the 

 wings, and by the quickness with which they are moved. A 

 small-winged bird may fly very fast by moving its wings with 

 great rapidity, and a large-winged bird may be a slow flyer if 

 it move its wings very slowly. But if two birds move their 

 wings the same number of times a minute,*that one will fly 

 the faster which has the longer wings, because it has the 

 greater leverage on the air. We shall notice too that all swift- 

 flying birds haxe very strong' primaries, and the stronger flyers 

 have also very long primaries. Long wings, long primaries, 

 strong primaries, make the work easier for the bird. 



Very swift birds one may expect to find with narrow wings. 

 The reason is that the wings are levers and their length and 

 strength give them their efficiency without regard to their 

 width. So the swifts and swallows and terns have very long, 

 narrow wings. Birds with wings both wide and long must 



