340 BIRD BEHAVIOUR 



grey, but often are white when young, white when 

 adult, or white all through life. These Herons are 

 simply liable to temporary or permanent albinism, 

 and in this connection it may be noted that there are 

 more all-white species among the Herons than in any 

 other group of birds ; incidentally also, the white 

 ones are just those which favour warm climates, 

 where they are most conspicuous, like the white 

 Cockatoos amongst the Parrots. Among Cockatoos 

 and Herons, grey and black are also common 

 colours, and all poultry-breeders know there is a 

 close affinity between grey, black, and white, so that 

 here laws of heredity have evidently determined 

 the colour, quite irrespective of assimilation to sur- 

 roundings. 



The reversion of the captive cock Linnet to the 

 young plumage in captivity is of interest in this 

 connection, as also the change of the red to yellow 

 in the males of some allied Finches, such as the 

 Crossbill and Rose-Finch (Carfodacus erytbrinus) ; 

 in old birds this seems to happen in the wild state, 

 and very old cock Linnets when wild seem to be- 

 come yellow where they should be red. The fading 

 of the red in both sexes of the captive Scarlet Ibis 

 (Eudocimus ruler) seems to be a matter of some de- 

 fect in the food ; it cannot be due to climate, as 

 this change occurred in the Calcutta Zoo, though 

 our old cock always put forth some scarlet splashes 

 in spring. Hen birds, being more delicate, might 

 be expected to feel the effects of captivity more 

 than cocks ; I noticed recently the hen of the Zoo 



