EVOLUTION OF THE COLORS OF BIRDS. 173 



black patch, the pigment having been directed to that 

 side of the shaft by natural selection but still insisting 

 upon following the conventional route of travel. 



The Calif ornian woodpecker (Melanerpes formicivorus 

 bairdi) affords several especially fine illustrations of color 

 for effect regardless of the laws of growth. Thus at the 

 line of demarcation of the white of the froxis and the 

 scarlet of the occiput, which is quite clearly cut, nearly 

 all the feathers are literally cut in two by the color, the 

 basal half being white and the distal end scarlet. Along 

 the sides of the head many of the feathers are scarlet 

 terminally and black basally, but I fail to discover any 

 feathers at the base of the scarlet patch which are black 

 terminally. Here again 'we have an illustration of how 

 natural selection must still be limited. The scarlet was 

 able to come in upon the white pigmentless feathers or 

 the white to encroach upon the scarlet, but the black did 

 not seem able to get a foothold upon the tips of the 

 scarlet feathers in a corresponding manner. 



The throat markings are interesting as being remark- 

 ably free from hybrid feathers. This is particularly the 

 case with the feathers of the black jugular patch where 

 it meets the yellowish crescent of the throat, hybrids 

 being almost wholly absent here. They also play a very 

 subordinate role at the lower end of the throat crescent 

 where it joins the black of the breast, although some of 

 the feathers here have a narrow edging of black. The 

 red-shafted nicker (Colaptes cafer) presents some interest- 

 ing features with regard to hybrid feathers. The red 

 malar streaks, or moustaches, occupy a tolerably dis- 

 tinct pterylographical area, and are well separated from 

 the feathers of the throat by a bare tract. Accordingly 

 hybrid feathers are almost or wholly wanting on the in- 

 side edge and rare on the outside of the streak. The 

 black crescent on the breast is of especial interest be- 



