HAWAIIAN BIRDS. 11 



causes. However, even the abandonment of forest tracts under 

 such circumstances seems inexplicable, and the writer can recall 

 no similar phenomenon among American birds. 



It cannot be doubted that the crowding together of the native 

 birds, as the direct effect of deforestation, will sooner or. later 

 have a disastrous efifect upon their welfare and numbers. As the 

 forest diminishes the food supply of the birds (insects, berries 

 and nectar) will diminish with it, and in time prove inadequate 

 to the demand. 



It is evident to all who have considered the subject that one 

 or more conditions of existence in the past have proved unfa- 

 vorable to the increase and spread of certain Hawaiian birds, 

 and have caused the extinction of others. The necessity of con- 

 tinuous inbreeding has been suggested as adequate to explain 

 the apparent inability of certain species to hold their own in the 

 struggle for existence, and, in the absence of other and more 

 tangible causes, certain facts relative thereto may be presented. 



It is apparent that the birds that are least numerous and that 

 live in much restricted habitats are the ones most subject to in- 

 breeding. Of such island species, Viridonia offers, perhaps, the 

 most marked instance, since it is confined to an area of but a 

 few square miles in extent, within which narrow belt of wood- 

 land the bird is by no means common. 



In such a case it would appear by no means improbable that 

 inbreeding has been a potent factor in the failure of the bird to 

 become numerous, and to extend its range into neighboring 

 districts, especially when to all appearances the latter are precisely 

 similar as regards their avian attractions and resources. 



It would appear that forms like Viridonia differentiated from 

 the parent stock and succeeded in maintaining themselves up 

 to a certain point and for a certain time, and then either re- 

 rnained stationary, in respect of numbers, or entered upon a 

 retrograde movement, tending perhaps, to ultimate extinction. 



No doubt there are many cases where it would be difficult to 

 determine whether a given rare and local form is at the begin- 

 ning of development or nearing the end of its career; but not so 

 in cases like Viridonia. A bird so very different from its allies 



