260 CALIFORNIA ACADEMY OF SCIENCES. 



and the ease with which it may be killed (see Coues' Key, 

 p. 578). Natural selection has consequently had com- 

 paratively little to do with modifying its colors, except 

 in supplying the recognition marks of the tail (see ante, 

 page 204). Nor has sexual selection had a very import- 

 ant part in modifying the colors, for although the colors 

 of the male are somewhat darker and more sharply cut 

 than in the female, this may be the simple result of 

 katabolism. The colored comb over the eye is, however, 

 unquestionably the result of sexual selection. The cross 

 barrings, however, were probably originally protective 

 in their nature, harmonizing with the lights in the forest 

 or the bark of trees, but they are fast becoming obliter- 

 ated by the increase in black. This increase would 

 naturally be most marked on the back where the greatest 

 amount of light falls. Young, brown, spotted protect- 

 ively marked. The different races are geographically 

 isolated, and have become distinguished by discrimina- 

 tive marks on the tail. 



GENUS BONASA. RUFFED GROUSE. 



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

 tral stage of adult. 



Prevailing colors, brown, reddish, gray, white, black. 



Colors protective, blending with the ground. Ruff of 

 male sexual. Black and light bars of the tail probably 

 directive marks, assisting in recognition in close flight. 

 Young, spotted, mottled and barred, the latter an inher- 

 itance from the adult, the former a retention of an earlier 

 form of plumage. The different races are due to environ- 

 mental influences, being darkest in the Northwest Coast 

 region and lightest in the Rocky Mountain district. 



GENUS LAGOPUS. PTARMIGANS. 



(4) Both sexes change with the seasons, in summer 

 plumage differing slightly; young differ slightly from 

 summer plumage of adults. 



