148 ORGANIC EVOLUTION 



and their noisy, jerky flight render them very conspicuous 

 when on the wing (Plate 83, L and M}. This makes their 

 sudden disappearance upon alighting all the more startling 

 and confusing. Any one who has attempted to catch the 

 common brown, roadside grasshoppers will, I am sure, ac- 

 cept this explanation of one use of the conspicuous color 

 of their hind wings. When at rest they can be seen only 

 by the keenest attention and closest observation, but when 



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in motion they are seen by the most careless observer. The 

 sudden mental change from careless observation of the 



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brilliant color and noisy flight to the close scrutiny necessary 

 to detect these grasshoppers when quiet is very difficult, and 

 is a change one does not succeed in making without much 



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practice. 



Some birds which are in general inconspicuously colored 

 have white or some other bright color upon the wing or tail 

 feathers, which becomes visible in flight. Examples are the 

 night-hawk, the Junco, the vesper-sparrow. The night-hawk 

 is so colored as to be observed only with great difficulty 

 when at rest upon a log or upon the ground (Plate 51, A\ 

 It often lies quiet, trusting to its inconspicuousness, until one 

 nearly steps upon it. When flushed, however, it flies away 

 with a jerky, zigzag flight, showing in the most conspicuous 

 manner its clear white spots upon the wings and tail (Plate 

 82, B\ The great contrast between its conspicuousness in 

 flight and its almost invisible character when at rest renders 



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it very difficult to find when it has alighted. 



Merriam would give a similar explanation of the use of 

 the conspicuous bands seen upon the hips and tails of 

 the desert Kangaroo rats and of the white under tail of the 

 antelope, squirrel, cottontail rabbit, and some of the jack 



