EVOLUTION OP THE COLORS OP BIRDS. 333 



marking. . Allusion has already been made to the use 

 of the chestnut color of the under tail coverts of Craleo- 

 scoptes as a recognition marking (see ante, p. 203), while 

 the black cap of this genus may serve a similar purpose. 

 The white wing and tail characters are either directive 

 or discriminative marks, and are very generally present. 

 When the adult are specialized beyond the streaked 

 plumage, either by the assumption of a uniform dark 

 color or of a dark back and light under parts, the young 

 show, to a more or less marked degree, the streaked or 

 spotted plumage of the ancestral form. I am unable to 

 suggest any explanation of the barred markings so com- 

 mon on the posterior part of the body among the wrens. 



FAMILY CERTHIID^. The Creepers. 



Genus Certhia. The Creepers. 



(1) Adult male like female; young like adult. 



Psevailing colors, brown, grayish, white. 



The colors of this genus are protective in nature, the 

 back harmonizing perfectly with the trunks of the trees 

 to which the bird clings. The breast is white in accord- 

 ance with the general laws of growth. 



FAMILY PARID^. The Nuthatches and Tits. 



(1) Adult male like female; young like adult (except 

 in Auriparus). 



Prevailing colors, black, white, brown, bluish, gray, 

 yellow. 



The birds of this family are highly specialized, al- 

 though never brilliantly colored. The primitive streaked 

 pattern is almost or completely wanting even in the 

 young plumage, showing that the specialization has been 

 carried very far. Auriparus is the only genus which 

 displays any bright colors, and in this instance the yel- 

 low head is obviously the result of sexual selection. 



