332 CALIFORNIA ACADEMY OF SCIENCES. 



birds has rendered necessary the white recognition 

 marks of the wing and tail. 



FAMILY CINCLID.E. THE DIPPERS. 



GENUS CINCLUS. THE DIPPERS. 



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

 and winter plumage slightly different). 



Prevailing colors, grayish, brownish, white. 



The colors are protective, harmonizing with the rocks 

 along the mountain streams frequented by these birds. 

 The white color of the edges of the feathers on the 

 lower parts of the body in young and winter specimens 

 points to an affinity to southern forms, in which the 

 under parts are white. Thus in G. leuconotus of Colom- 

 bia and Ecuador the entire under parts, head and 

 middle of back are white. The adult of G. ardesiacus 

 of Costa Rica is very similar to G. mexicanus, but the 

 breast of the young is almost pure white. Why there 

 should be an increase in pigment toward the north in- 

 stead of the reverse, as is the rule, I cannot suggest. 



FAMILY TROGLODYTID^E. THE WRENS, THRASH- 

 ERS, ETC. 



(1) Adult male like female; young like adult, or (2) 

 young with a peculiar first plumage. 



Prevailing colors, black, white, slaty, gray, brown, 

 rufous, chestnut. 



These birds are, as a rule, not highly specialized, so 

 far as their colors are concerned, reminding one of the 

 general plan of color markings among many of the 

 sparrows. As a rule, the back is some shade of brown 

 or rufous, with the breast white, and either the breast 

 alone, or sometimes both back and breast, profusely 

 streaked or spotted. Sexual selection has had, it would 

 seem, but a subordinate part in producing this plan of 



