196 CALIFORNIA ACADEMY OP SCIENCES. 



are colored upon the upper part of the body some 

 mottled shade of brown or dun, which blends wonder- 

 fully with the ground upon which they alight. The 

 perfection of protection of the colors of the nighthawk 

 and whip-poor-will which sleep in exposed places during 

 a large part of the day, is a source of wonder to every 

 country boy. Most of the smaller flycatchers are so ob- 

 scurely clad and blend so completely with the branches 

 upon which they alight, that in walking through the 

 forest the observer frequently knows them simply as 

 riKV, et pra'tera, nihil. The horned lark as it squats upon 

 the plain is often nothing but a song in the air, and 

 defies the closest scrutiny. Most of the sparrows, in the 

 general style of their dress — Zonotrichia, Spizella, Mel- 

 ospiza, Peucsea and Passerella, are colored harmoniously 

 with their environment. The buff and olive green of 

 most of the vireos make them very difficult to detect, 

 even when singing close at hand. So also with the 

 wrens, titmice and thrashers. 



It will be noticed that species habitually found near 

 the ground are generally colored brown, while species 

 found among the trees are either greenish or olive, as 

 with so many of the vireos, warblers, etc., or gray, the 

 colors thus blending either with the leaves or branches. 

 I would suggest that there is great probability that the 

 habits of birds have been more or less determined by 

 their colors. If, for example, the natural color of the 

 pigment of a group of birds was olive green or gray, 

 those individuals which formed the habit of living 

 among the trees would survive, those frequenting the 

 ground, being more conspicuous, would perish. Still 

 more probable is it that, other things being equal, the 

 brown birds which got up among the trees would be de- 

 stroyed, while those which remained near the ground 

 would live. 



