BIRDS 103 



occasionally tilting the wings and tail to better catch the 

 shifting breezes, uses the latter method. Most birds fly 

 mainly by strength, but the hawk, eagle, and albatross fly by 

 skill; that is, they soar on the wind without much muscular 

 effort. 



The wing of a bird is suited to its peculiar needs. Gulls, 

 hawks, and swallows, much on the wing, have large wings, 

 and chiefly soar. The robins, sparrows, blackbirds, etc., 

 which live mainly on the ground, or skulk about the bushes, or 

 flit among the trees, do not need the power of long flight. 

 They generally fly by easy stages. But they need the power 

 of rising quickly from the ground when startled. So their 

 wings are broad, rounded, and concave underneath, so as 

 to resist the air well. The quail, partridge, and sparrow 

 cause a rustling sound by the rapid fluttering of their wings 

 on starting from the ground. The humming-bird makes its 

 wings go so fast that you cannot see them, and the buzzing of 

 the wings gives it its name. Birds of long wing, like the 

 duck, gull, and albatross, cannot rise well unless they run 

 or swim quickly on the level till they get the necessary speed 

 to enable them to rise on the air. 



Strange as it may seem, because one of the chief distinc- 

 tions of birds is flight, there are some birds that have given 

 up the habit of flying, and by disuse the wings have be- 

 come rudimentary or have degenerated into organs for other 

 purposes. This degeneration is greatest in the cassowary, 

 emu, and apteryx, which have almost no wings at all. The 

 ostrich has rudimentary wings unfit for flight, but which are 

 still flapped while running. These birds depend upon their 

 legs for escape. The penguins are marine birds, chiefly 

 in arctic waters, which use their wings as flippers in swim- 



