WHITE BLACKBIRDS AND OTHER FREAKS. 117 



always so. Caged birds sometimes turn dark in moulting, 

 and then moult back again. A robin that was black in 

 infancy afterward acquired white wings and a white tail; 

 while another that was caged for six years was normally 

 colored for the first two years, on the third showed some 

 white and some black feathers, on the fourth, white wings 

 and tail and a black breast, with red under the wings and a 

 white belly. The fifth year it was normally colored, and the 

 last year it was red below and black above, with white wings 

 and tail. 



The " color phases " already mentioned form another class of 

 oddities. No one knows the reason, but among certain groups 

 of birds it is common or usual for individuals to be some of 

 one color, some of another, all their lives. They look like 

 entirely different species of birds, and yet scientists agree that" 

 they are not. This is a very common freak among some of 

 the sea-birds, especially the jaegers and the shearwaters, in 

 which the light and dark phases are well recognized. In one 

 genus of owls, and in one or two of the heron kind, something 

 like it occurs. Of two little screech owls from the same nest, 

 one will sometimes be gray and the other reddish brown, and 

 so far as is known they will keep their color all their lives. 

 This phenomenon is sometimes called dichromatism or double 

 coloring. In one of the little bitterns a supposed black di- 

 chromatism has been discovered, while in the reddish egret a 

 white dichromatism has been known for many years. The 

 young of certain herons are white, while the old birds are very 

 dark colored ; but this is not called dichromatism, because the 

 color depends upon the age of the bird. However, among the 

 reddish egrets specimens are frequently seen which are white 

 all their life. It is not albinism, because the white is always 

 pure white, and the iris is not pink, but white. The dark 



