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 plain 

 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. bilineata) as distinguished from the the supraloral 

 white spot in other species, is a discriminative mark 

 apparently. The evolution of the black throat-patch 

 may be traced from the sage sparrow ( 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^EA. 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 



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



