PARROT ABNORMALITIES 339 



fore no doubt, like human beings similarly afflicted, 

 probably have bad sight, so that they are unfitted to 

 survive in a state of nature. The white Australian 

 Hawk (Astur novce-hollandice) with its black-pupilled 

 red eyes, thrives well enough, incidentally showing 

 that there is no need for a bird of prey to resemble 

 its surroundings for aggressive purposes. 



Particularly interesting are the cases in which a 

 bird varies into a different style of plumage than 

 the black, pied, white, yellow, or so forth ; thus, 

 the brown Kaka Parrot (Nestor meridionalis) of 

 New Zealand often produces a more or less red 

 variety in nature; and in captivity I have seen a 

 specimen of the very rare Derbian Parrakeet (Pala- 

 ornis derbianus) at the Zoo become a different bird 

 altogether, its pinkish breast turning green like 

 the back, and its grey cap black like the throat, so 

 that any one would have called it a distinct species, 

 while its cage-mate remained unaffected. It after- 

 wards, however, returned to its original colour, and 

 this is always liable to happen with abnormally 

 plumaged birds, unless they are pink-eyed albinos 

 or lutinos, in which the abnormal plumage is per- 

 manent, so far as I know. 



And as a bird may get more or less white with 

 age, in captivity, as sometimes happens with the 

 Linnet and usually with black breeds of the common 

 Duck, it does not need Darwin's far-fetched theory 

 about sexual selection and changes of taste in the 

 females to account for the peculiar case of the Reef- 

 Herons (Demiegretta) in which the birds should be 



