158 CALIFORNIA ACADEMY OP SCIENCES. 



(Sialia arcticd), in which the belly and under tail coverts 



are white. In the following, blue is the conspicuous 



color: 



Cyanocitta. Guiraca cceritlea. 



Aphelocoma. Passerina amcena. 



Cyanocephalus cyanocephalus. Evjjhonia elegantissima . 



Dendroica ccerulea. 



It is a fact worthy of note that blue very rarely occurs 

 in limited patches or markings. There are a number 

 of species in which the general shade of color is ap- 

 proaching a clear blue, as in the blue-gray gnatcatcher 

 (Polioptila ccerulea)^ the yellow^-rumped warbler (Den- 

 droica coronata), and a number of others of the same 

 genus; but where do we find, among North American 

 birds, species with blue heads, ear coverts, throat patches, 

 wing markings, or spots in general? The green-jay 

 (Xanthoura luxuosa) with its bright blue head is a strik- 

 ing exception. 



It will not be necessary to consider green at any 

 length, for the simple reason that there are hardly any 

 species in which a pure green figures at all, the above- 

 mentioned jay and the parrots being exceptional cases. 

 The metallic greens, as in the humming birds, are prob- 

 ably not pigmental in nature, and hence must be ex- 

 cluded. As an olive green it is frequently found, how- 

 ever, but we are at present concerned only with the pure 

 colors. 



A few generalizations from the forgoing facts may 

 now be in order. It will be noticed that with a very 

 few exceptions (Buteo and Dendroica) pure color in 

 large masses occurs in small genera. Black forms are 

 scattered through various families, from the lowest to 

 the highest. White reaches the climax of its develop- 

 ment among the Falconidse and Bubonidse; red among 

 the Fringillidse and the allied Tanagridse; yellow among 



