The Making of Species 



defend themselves. In this connection it is inter- 

 esting to notice that in New Zealand all birds, 

 whether introduced or indigenous, are particularly 

 liable to albinism. Owing to the fewness of their 

 enemies these albinistic forms are able to persist. 



A variation, or rather a mutation, that fre- 

 quently occurs among domesticated birds, but 

 which is seen in very few wild species, is that 

 which takes the form of white primary feathers 

 on the wing. This variation must often occur in 

 nature, but it rarely establishes itself, apparently 

 because white feathers do not resist wear so well 

 as coloured ones do. 



Black-and-yellow colouration occurs in several 

 widely separated species of birds. The arrange- 

 ment of the two colours follows to some extent 

 the same rules as the black-and-white combination. 



Several birds have a yellow body with black 

 head, wings, and tail, such as 



The Black - headed Oriole (Oriolus melano- 

 cephalus). 



The Black-and-Yellow Grosbeaks (Pycnor- 

 hamphus icteroides, P. affinis) (cock). 



The Common Troupial (Icterus vulgaris). 



In others the black on the head is nearly or 

 quite suppressed, that on the tail remaining to a 

 greater or less extent ; such are 



The Golden Orioles (Oriolus galbu la, O. kundoo, 

 etc.). 



Several species of Icterus. 

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