INTERESTING PROBLEMS CONCERNING THE AVIFAUNA 355 



the feathers to develop properly, and as the red-fronted parrakeet 

 sometimes shows this variation in New Zealand, it seems probable 

 that the yellow parrakeet originated independently in both islands 

 from different flocks from New Zealand. It is probable that the 

 small number of individuals which arrived at each of the islands 

 allowed the variation to obtain a permanent influence, which it 

 could not do in New Zealand, on account of the large number of 

 birds, and, consequently, the greater facilities for inter-crossing. 

 Thus, we have a new species produced by the isolation of a few 

 individuals. We also have a ease of the double origin of the same 

 species. This last cannot occur often ; but it shows that the great 

 differences between the climates and vegetation of Antipodes 

 Island and Maequarie Island failed to produce any effect. 



New Zealand ornithologists have special advantages for study- 

 ing the effects of the absence of enemies on development, the 

 most important of which is degeneration in the powers of flight. 

 No part of the world offers so many examples of degeneration in 

 the wings of birds as New Zealand does. There are strong flying 

 birds, such as the quail hawk, the kea, the parrakeets, and ducks ; 

 as well as a chain of more or less degenerate birds, passing 

 through the tui, the thrush, the crow, the huia, and the fern-bird, 

 to the kakapo, the wood-hens, the flightless duck, and the kiwi, 

 none of which can fly at all. In these non-flying birds there are 

 some with large wings, like the kakapo, others with small wings, 

 such as the wood-hens and the kiwi, and there are no wings at all 

 in the extinct moas, in most of which even the shoulder-girdle had 

 disappeared. 



In some of the outlying islands, the snipes, the larks, and the 

 parrakeets are feeble fliei-s, although their relations in New 

 Zealand fly well. So general an effect upon birds of so many 

 dift'erent kinds must be due to some general cause; and we find 

 it in the baneful effects of the want of competition. The fact that 

 on some of the outlying islands there are several birds with feebler 

 powers of flight than their congeners in New Zealand, although 

 they have no more enemies in New Zealand than on the islands, 

 is very remarkable. We may accept natural selection as the cause 

 of loss of powers of flight when that loss has been useful to the 



