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 (Oviolus melano- 
cephalus). 
The Black-and-Yellow Grosbeaks (Pycnor- 
hamphus icterordes, P. affinis) (cock). 
The Common Troupial (Jc¢erus 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 (Ovzolus galbula, O. kundoo, 
etc.). 
Several species of Lcderus. 
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