146 AFRICAN GAME ANIMALS 



of small birds. In temperate North America two of the most 

 abundant small birds are the song-sparrow and the junco, 

 each in various forms; their ranges are largely the same; 

 their habits are alike as regards taking cover, etc.; one is 

 streaked and spotted, one is of a slate-like unicolor, with a 

 white belly; they are strikingly contrasted in coloration — as 

 much as are the cock and hen ostrich; and yet they are 

 equally successful in life. The same is true as regards in- 

 digo buntings and field-sparrows, seaside and sharp-tail 

 finches, towhees, catbirds, mockers, and thrushes. As 

 regards the great majority of mammals and birds, it is evi- 

 dent that natural selection, using concealing coloration as a 

 survival factor, has had nothing whatever to do with pro- 

 ducing their patterns and tints; and where it has worked 

 at all — and in many, probably in most, species it has had 

 no effect whatever — it has only been by setting wide limits 

 beyond which the variation cannot go. In all these cases 

 countershading has but little effect and cannot possibly be 

 a survival factor. 



There remain the numerous cases, especially numerous 

 among young mammals and birds, where the coloration 

 has an undoubted concealing value, probably sufficient to 

 make it a survival factor. Although numerous, these cases 

 are far outnumbered by the others already discussed. In 

 most of these cases it is probable that natural selection has 

 kept the coloration concealing, but it is improbable that it 

 has produced either the exact pattern or the exact tint. In 

 a few of these cases countershading helps the concealing 

 quality of the coloration; but it usually ceases to act when 

 the animals have most need of concealment, and crouch to 

 avoid notice. The probabilities are overwhelming that it 



