EVOLUTION OF THE COLORS OP BIRDS. 293 



shown by their incomplete development in winter, when 

 the color is yellow and much broken. Sexual intensi- 

 fication has, in this instance, been an important factor 

 in the development of the specialized colors of the male, 

 the red of summer being merely an intensification of 

 the yellow, which still persists in winter, and the black 

 an intensification of the brown. 



The ancestral bird was a brown streaked bird, lighter 

 or white on the breast. 



GENUS STURNELLA. THE MEADOW LARKS. 



(1) Male similar to female (the latter duller); young 

 similar to adult, but duller. 



Prevailing colors, black, white, brownish, grayish, 

 yellow. 



The colors of this genus suggest somewhat an affinity 

 with the orioles (Icterus). The browns and grays of the 

 back are protective in nature, harmonizing with the 

 ground, and the yellow breast and black crescent are 

 probably due, in some measure at least, to sexual selec- 

 tion, partly transferred to the female by heredity. There 

 are slight seasonal as well as sexual differences, the full 

 breeding plumage being produced by the wearing away 

 of the tips of the feathers, but the change is not a very 

 marked one. The intensification of the yellow into its 

 correlative red in the tropical representative of the genus 

 has already been mentioned (see ante, p. 156). 



GENUS ICTERUS. THE ORIOLES. 



(7) Adult males more conspicuously colored than 

 females; young generally similar to female; young male 

 (second year) intermediate between adult male and 

 female. 



Prevailing colors, black, white, yellow, orange, red, 

 brown, olive green, gray. 



This genus affords an especially good illustration of 



