68 THE FLIGHT OF BIRDS. 



The Ostrich has no keel, and is incapable of flight. 

 The Hoatzin, that curious South American bird, 

 according to all observers a most feeble flyer, has 

 the front part of the keel missing. In every case 

 the shape of the keel has its significance and is well 

 worth observing, since it indicates the style of flight. 

 The Duck and the Guillemot, having very long 

 breastbones and keels, have of course very long 

 flight muscles and a long muscle is capable of more 



Fig. 18. 



Breastbones of (1) Guillemot — actual length of keel 5k inches. 



(2) Falcon. Drawn to scale. Compare that of the Adjutant, 



a Stork famed for his soaring. 



contraction than a short one. A glance at their 

 breastbones, therefore, tells us that they are birds 

 that fly with a long stroke. A Guillemot's wings are 

 so small that a long, strong stroke is a necessity 

 for him. A Duck, during horizontal flight, does 

 not raise his wings very high, but the stroke is pro- 

 longed till the wings can strain no further downward. 



