evolution of the colors of birds. 307 



Genus Amphispiza. Black-throated Sparrow, etc. 



(2) Adult male like female; young like some ances- 

 tral stage of the adult. 



Prevailing colors, black, white, gray, brown. 



Although the colors of this genus are decidedly 2:)lain 

 the markings are considerably specialized, the general 

 tendency of coloration being solid rather than streaked, 

 and the special markings being strongly developed. The 

 white superciliary stripe of the black-throated sparrow 

 (A. hilineata) as distinguished from the the supralaral 

 white spot in other species, is a discriminative mark 

 apparently. The evolution of the black throat-patch 

 may be traced from the sage sj^arrow (A. belli nevadr.nsis) 

 where the " sides of throat [are] marked with a series of 

 narrow dusky grayish streaks, but no continuous stripe," 

 through Bell's sparrow (A. belli) which has the '' sides 

 of throat marked with a broad continuous stripe of 

 blackish," to the Mexican forms in which we find the 

 " upper part of throat black, the point of the chin white; 

 fore-neck and lower part of throat uniform ash gray;"* 

 and finally A. bilineata is reached with the throat com- 

 pletely black in the adult but white in the young. It is 

 doubtless a directive mark, although possibly discrim- 

 inative in function. 



Genus Peuc^.a. Rufous-crowned Sparrow, etc. 



(2) Adult male like female; young like some ances- 

 tral stage of the adult. 



Prevailing colors, blackish, white, ashy, rufous, brown. 



The plan of coloration in this genus reminds one 

 greatly of Spizella, particularly in the presence of a 

 rufous crown patch in some species and the substitution 

 of streaks on the top of the head in others. The young 

 are much more decidedly streaked than the adult, there 



* Kidgway's Manual, pp. 425-426. 



