No. 573] 



:>r>7 



and so not much developed. It is noticeable that white 

 patches in the wing are often of such a nature that they 

 are concealed through the folding of the wings when the 

 bird is at rest. This accords with my belief that while 

 in flight the bird is unavoidably conspicuous by reason 

 of its motion, and that white patches showing at such 

 times add little or nothing to the disadvantage. In the 

 hairy and the downy woodpeckers (Dn/nlmtes), a white 

 stripe down the back is developed as part of the pattern, 

 and no doubt as in many mammals, marks the separation 

 between the pigment areas of opposite sides. Centrifugal 

 pigmentation is seen in some species as the kittiwake in 

 which the outer primaries are black. 



The side patches are commonly continuous with those 

 of the shoulders, and when ventrally restricted, give a 

 white abdomen. Their median separation dorsally, is 

 seen in the hairy and downy woodpeckers as above noted. 

 I have not studied any special developments of these 

 areas, and they are commonly small. 



The Rump Patches. — In birds as in mammals the two 

 rump patches pigment the posterior extremity of the 

 body. Their ultimate centers are dorsal and so close to- 

 gether that it is much less common for them to be sepa- 

 rated medially than to be restricted laterally. With a 

 slight areal reduction, a separation takes place between 

 them and the side patches dorsally, so that a white area 

 on the rump results. Often this white area represents 

 doubtless a slight restriction of both sets of pigment 

 patches which by drawing farther apart increase the 

 white area along the lower part of the back. In the 

 domestic pigeon much variation may be found, from a 

 condition in which the lower back is wholly pigmented 

 to one in which it is mostly white. The primary break 

 which causes this white patch has been much developed 

 in many groups of birds as a particular mark in the 

 pattern. In many species it is simply of a paler hue than 

 the surrounding parts as in the yellow-rumped warbler 

 (Dendroica coronata) or the pine grosbeak (Pinicola). 



