300 A HISTORY OF BIRDS 



In the Pacific Heron {Notophoyx pacified) the adult is of 

 a glossy olive green and slate colour, blackish below, relieved 

 by broad longitudinal streaks of white, and white tips to the 

 feathers of the forepart of the neck. Occasionally nearly white 

 adults are met with. From this we pass to the African white- 

 throated Reef-heron {Lepterodias gularis) wherein the adults 

 are slate coloured, and the white phase occurs with more fre- 

 quency. The nearly allied Indian Grey Reef-heron (Z. ashd) 

 is yet paler, and also develops a white phase. The Reddish 

 Egret {Dichromanassa rufd) carries us a stage further, the 

 general colour of the adult being of a light slaty grey, relieved 

 by cinnamon on the head and neck. The immature birds are 

 either bluish-grey or white. Finally, in the Blue Heron {Florida 

 ceruled) the adults are of a bluish-slate colour, while the young 

 birds are apparently always white. Frequently this white 

 plumage is retained throughout life. 



Whether the undoubted tendency to whiteness which is here 

 apparent gains intensity, and ultimately becomes a dominant 

 character, which has become favoured by selection, or whether 

 the evolution of white species has been brought about by 

 geographical isolation is a moot point, which demands further 

 investigation so far as this is possible. 



Apparently coming within the category of dimorphism are 

 the curious colour aberrations known as " hepatic phases," of 

 which good instances are furnished by the Tawny Owl and 

 the Common Cuckoo. These species respectively not infre- 

 quently develop individuals which have excited not a little 

 attention from the fact that they differ from the typical forms 

 of their respective species in that the plumage is of a peculiarly 

 red or ferruginous hue while preserving all the characteristic 

 markings belonging to that species. So far, however, it would 

 appear that such examples are immature. It should be men- 

 tioned, however, that a case is on record of an American Tufted 

 Owl {Scops asio), in confinement, which passed from the grey 

 into the red phase. Such ferruginous types are indeed among 

 the Owls by no means uncommon, and are especially frequent 

 in the Genus Scops. The Night-jar and the Common Snipe, 

 among other species, also occasionally develop these furruginous 

 types. 



The Common Snipe is further remarkable in that it occasion- 



