356 THE ANIMALS OF NEW ZEALAND 



species : as in the case of parrakeets and the larks on small islands 

 much exposed to gales of wind, as the Antipodes. But this will 

 not apply to the flightless duck of the Auckland Islands, or to 

 any of the birds on the main islands of New Zealand. Who can 

 doubt but that the kakapo and the wood-hens would be benefited 

 by being able to fly? 



The pectoral muscles of the tui have remained unaltered in the 

 Auckland Islands, Avhile in the parrakeets and larks they have 

 been reduced. But the Auckland Islands are large, and have 

 plenty of shelter, and it is not easy to believe that parrakeets and 

 larlcs would be blown away from them. It is quite impossible 

 to believe that the flightless duck should be in any such danger ; 

 so that, as the explanation of natural selection here fails us, we 

 may doubt its effects in other cases. 



As already stated, in New Zealand we cannot trace the action 

 of natural selection in bringing about the degeneration of the 

 wings of so many birds, some of which inhabit the forests and 

 others the open country. It is in the absence of competition, 

 combined with an abundant supply of food, and consequent 

 disuse of the wings, that we nnist look for the cause of the loss 

 of their powers of flight. 



An examination of the birds shows that in most cases the crest 

 of the breast-bone diminishes first, then the wing's are reduced 

 in size (first the feathers then the bones), until at last they 

 disappear altogether. That is, the muscles get weak before they 

 get smaller, while the wings remain large long after the muscles 

 are too small to employ them efficiently. 



How to account for this has always been a difficulty. 



It has been suggested that natural selection, acting through 

 the law of economic nutrition in periods of scarcity of food, 

 would cause the degeneration of an organ which was of little 

 or no use. The useless organ, it is thought, would not require 

 nourishment, and would dwindle away, to the advantage of the 

 rest of the animal. But for this explanation to hold good, it has 

 to be established that periods of semi-starvation actually occur, 

 and that when they occur, the iLseless organs suffer more than 

 other parts of the body. 



