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THE AMEBIC AN NATURALIST [Vol. XLVIII 



In others the tendency to albinism thus expressed has 

 gone farther so that a pigmentless spot is formed. This 

 white rump patch is present in many unrelated groups 

 of birds in which it has independently arisen through 

 parallel development. Thus it is seen in many of the 

 smaller petrels, in the palm swift, the flicker woodpecker, 

 the white-rumped and other sandpipers, the white- 

 rumped shrike, the European house martin and others. 

 The tail feathers are pigmented by these patches, and 

 among various species show many steps in the process 

 of pigment reduction. As in the domestic pigeon, occa- 

 sional albinistic individuals show white outer tail 

 feathers, in accordance with the rule that the first pig- 

 ment reduction takes place at those parts of the primary 

 areas that are farthest removed from the pigment centers. 

 I have seen a white outer tail feather in wild specimens 

 of song sparrows and Lincoln's sparrow and it is occa- 

 sional in other species. In others again this mark has 

 become developed and fixed as a species character. Thus 

 in the bay- winged bunting {Pocecetes gramineus) there 

 is a single white outer feather on each side, in the junco 

 {J unco hy emails) there are two. A white central tail 

 feather is much rarer, but a pure white tail is found occa- 

 sionally as in the hummingbird, Loicurin phalerata, the 

 bald eagle and certain gulls, due to the permanent reduc- 

 tion of the pigment area of the rump at this extremity. 

 I once examined an albino ruffed grouse (Bonasa) which 

 was entirely white except for a single feather among the 

 upper tail coverts at the left side of the rump. This 

 blemish in the otherwise pure white bird seemed inexpli- 

 cable to those who examined it with me, but it merely 

 represents the last remnant of the left-hand rump patch, 

 still persisting though all the other pigment centers were 

 inactive. 



It is very interesting that the white rump mark, so 

 commonly found in unrelated groups of birds, is one 

 which is conspicuous in flight only, and the same is true 

 of many of the white tail marks, such as outer white 



