170 Jenkins, Variation in the Hairy Woodpecker. [April 



Thus not only would the bird more nearly resemble the background, 

 but the attractive feature of large white spots on black feathers would 

 be done away with. To reduce the white on the closed wing it was 

 only necessary to eliminate the spots from the exposed portions of 

 the feathers, namely the outer webs and the ends of the flight feathers 

 and coverts, for the inner web of each flight feather is covered by the 

 outer web of the preceding feather and only the distal ends of the 

 coverts are exposed. This is just what we have in the Western 

 Hairy Woodpecker wing. The spots on the outer webs of the sec- 

 ondaries are reduced to a single one at the base of each feather, 

 which is always hidden by the greater coverts. The spots on the 

 exposed parts of the greater coverts an' reduced in number and 

 size, or more commonly are entirely absent, and the spots on the 

 median coverts are either absent or reduced to a mere streak. Sev- 

 eral spots on the outer webs of the primaries still persist but they 

 are fewer in number and are much reduced in size and are con- 

 sequently very inconspicuous. 



When the bird is in flight it does not need this protective colora- 

 tion but probably does need the spots for the same purposes for 

 which they were originally developed, and we find that nearly all 

 of the spots on the parts of the wing that were unexposed when it 

 was closed, namely those on the inner webs of the flight feathers, 

 are still retained. The inner web of the secondary has lost only 

 the outermost spot, and the inner web of the primary the three 

 outer spots, but these were the smallest spots in the eastern bird 

 and of the least importance. When the bird flies, the wing is 

 thrown up as often as down, and the striking contrast of white 

 and black is about, though not entirely, as effective as before to 

 all observers except those that may be directly overhead. 



Thus we have the least possible contrasting shades on the bird 

 at rest combined with the greatest possible contrasts on the 

 bird in flight, and given that the contrast in flight is of use to 

 the bird, then this combination is an advantage and was devel- 

 oped as such. 



Could this theory be absolutely proven we would still have to 

 explain why all of the Hairy Woodpeckers have not developed in 

 like manner. If we draw a geographical line between light and 

 heavily spotted forms this line would in part coincide with the geo- 

 graphical line between the Arid West and Humid East. But I 



