Vol. IV. 

 1905 



] HUTTON, Lcuid Birds of New Zealand. Qg 



Who can doubt but that Stringops and Ocydrotnus would be 

 benefited by being able to fly ? 



I find that the pectoral muscles of Prosthemadcra have re- 

 mained unaltered in the Auckland Islands, while in the Parrakeets 

 and the Larks they have been reduced. But the Auckland 

 Islands are large and with plenty of shelter, and it is not easy 

 to suppose that Parrakeets and Larks would be blown to sea 

 from them, and it is quite impossible that the flightless Duck 

 {Nesonettd) should be in any such danger ; so that as the ex- 

 planation of natural selection here fails us we may doubt its 

 effects in other cases. 



Also in New Zealand we cannot trace the action of natural 

 selection in bringing about the degeneration of the wings in 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 the consequent disuse of 

 the wings, that we must 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 sternum diminishes first, then the wings are reduced in 

 size — first the feathers, then the bones — until at last they dis- 

 appear 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 efflciently. (See Appendix.) 



How to account for this has always been a dif^cult\'. It has 

 been shown that panmixia, although allowing detrimental 

 variations to exist, which could not be the case where competi- 

 tion is keen, cannot be a cause of progressive degeneration, for 

 it has no directive power. It has also been suggested that 

 natural selection, acting through the law of economic nutrition 

 in periods of scarcity of food, would tend to 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 

 useless organs suffer more than the other parts of the body. 

 Let us see if the birds of New Zealand can throw any light on 

 this matter. 



First as to the periods of semi-starvation. — Among the Passerine 

 birds there are in New Zealand four genera of Muscicapidce 

 {Petroeca, Miro, Pseudogerygone, and Rhipidurd), and three of 

 XenicidcB {Acaiithidositta, Xenicus, and Traversia), which live 

 chiefly on insects, and it seems almost certain that these birds 

 must be pushed very hard for a living every winter. There 

 are also nine genera of seed or grub eaters, and these can have 

 no periodical famine time ; for their food is abundant all through 

 the year. But none of the insect-eating birds show deteriorated 

 powers of flight, while among the others we have Heteralocha, 

 which seldom attempts to fly; Turnagra, which cannot rise into 



