Bird Flight 187 



as it holds them outspread while it skims over the plain, 

 perhaps using them mainly as outriggers or balancing 

 poles in its swift passage on its stilt-like legs. The penguins 

 convert their wvngs into fins while swimming through 

 the water, the feathers closely resembling scales. 



There are birds of many kinds, and therefore a great 

 variety of wings and modes of flight. Birds with short, 

 broad, rounded wings, with the under surface slightly 

 concave and the upper surface correspondingly convex, 

 usually have comparatively heavy bodies, and race 

 through the air with rapid wing-beats and rather labored 

 flight, and compass only short distances. Among the birds 

 of this kind of aerial movement may be mentioned the 

 American meadowlark, the bob-white, and the pheasant. 

 Other species propel themselves in rapid, gliding, and 

 continued flight by means of long, narrow, and pointed 

 wings, like the swifts, swallows, and goatsuckers, while 

 many others, notably herons, hawks, vultures, and eagles, 

 are distinguished by a vast alar expansion in proportion to 

 their weight, and hence are able to sustain themselves in 

 the air by sailing, with only a slight stroke at rare inter- 

 vals. Such birds as the stormy petrel and the frigate- 

 bird have wings that are broad, corvex, and of great 

 length in contrast with the lightness and small bulk of 

 their bodies, for which reason they are able to sustain 

 themselves in the air for days without rest. It is even 

 thought that some of these wonderful birds of the limitless 

 ocean sleep on the wing, though how such an hypothesis 

 could be proved it would be difficult to say. 



