68 THE FLIGHT OF BIRDS. 
The Ostrich has no keel, and is incapable of flight. 
The Hoatzin, that cfious 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 
Fia. 18. 
Breastbones of (1) Guillemot—actual length of keel 54 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. 
