272 CALIFORNIA ACADEMY OF SCIENCES. 



GENUS POLYBORUS. CARACARA. 



(2) Adult male like female; young with peculiar first 

 plumage. 



Prevailing colors, black, white, brown. 



It is difficult to suggest any use for the striking distri- 

 bution of color marks in this genus. There are three 

 species, in general much alike. The Guadalupe Island 

 form (P. lutosus) is of peculiar interest from an evolu- 

 tionary point of view. Left stranded upon this island 

 without any more powerful rival, and from its habits of 

 feeding on carrion, without any need of agressive resem- 

 blance, it has been perfectly free to develop its own life 

 history independent of the bulk of its own species or of 

 natural selection (so far as its colors are concerned). 

 Some of the points in which the island species has varied 

 from the parent form may be tabulated as follows from 

 the description in Ridgway's Manual: 



cheriway. lutosus. 



Rump white (with or without bars). Rump dull brownish buff, broad- 

 ly barred with dull brown. 



Tail white, the narrow bars grayish. Tail brownish buff, broad bars of 



grayish brown, bordered by nar- 

 rower zigzaggy lines of dusky. 



Terminal dark band 2-in. or more Terminal dark band less than 

 wide. 2-in. wide. 



GENUS PANDION. OSPREY. 



(2) Adult male similar to female; young somewhat 

 different from adult. 



Prevailing colors, brown, gray, white. 



The young differ from the adult simply in having the 

 dark feathers of the back tipped with white or buffy. 

 The coloration does not apparently serve any useful 

 purpose. 



