288 CALIFORNIA ACADEMY OP SCIENCES. 



est form is found in the northwest coast region and the 

 palest varieties in the western desert region, particularly 

 of Lower California. 



The young are strikingly different from the adult in 

 colors and markings. The plumage is generally very 

 much darker, sometimes being almost black and the 

 feathers are tipped with white. From the darker and more 

 closely spotted head of the young it seems probable that 

 the ancestral bird had a black head. This has become 

 modified in the adult into a very unusual pattern on the 

 side of the head, which is doubtless a recognition mark 

 of some sort. It should be pointed out that the colors 

 of this genus hardly appear to harmonize with the law 

 of the assortment of pigment, for the special colors be- 

 ing black and yellow we should expect the generalized 

 colors to be olive green instead of brown tending toward 

 rusty or vinaceous. 



FAMILY CORVID^. The Crows, Jays, Magpies, 



ETC. 



(1) Male like female; young like adult, but colors 

 sometimes less distinct. 



Black, white and blue are the characteristic colors of 

 this specialized family. Gray is also present as a gen- 

 eralized color, and much more prevalent than brown. 

 Yellow and green occur only in one tropical genus, 

 Xanthoura. 



There is a strong melanistic tendency in this group, 

 due to the high specialization and the fact that from 

 their powerful size and gregarious habits these birds 

 have few enemies to contend with. The generalized 

 gray is due to the combination of the specialized blue 

 and black. Sexual selection has apparently been instru- 

 mental in the development of the blue pigment among 

 the jays, although it has become completely transferred 



