GEOGRAPHIC DISTRIBUTION OF ANIMALS: OCEANIC ISLANDS 



297 



example of adaptive radiation among birds. The Hawaiian Islands are the 

 home of a distinctive group of birds called "sicklebills," "honey creepers," 

 or, better, "drepanids," from the name of the family to which they belong: 

 Drepaniidae (Drepanididae). The fact that they are thus placed in a sepa- 





FIG. 13.8. The woodpecker finch and its stick. (Drawn by 

 Roland Green from photographs by R. Leacock; from Lack, 

 Darwin's Finches, Cambridge University Press, 1947, p. 59.) 



rate family by themselves reflects their dissimilarity to all other birds. 

 There is, indeed, considerable doubt as to their closest continental rela- 

 tives. Present evidence suggests that their ancestors were allied to the honey 

 creepers of tropical America (Family Coerebidae). 



The Hawaiian Islands occupy an isolated position in mid-Pacific, far 

 from any continent. North America is about 2000 

 miles away, Japan more than 3000 miles. The 

 archipelago is even remote from other large oceanic 

 islands. The view is sometimes advanced that the 

 Hawaiian Islands were once joined to a still-existing 

 continent or to a mid-Pacific continent which later 

 sank below the waves. The more widely held view, 

 however, is that the islands, of volcanic origin, rose 

 directly from the ocean floor and were never con- 

 nected to other bodies of land. 



As would be expected in truly oceanic islands far from a continent, the 

 number of land birds in the Hawaiian Islands is small. Also this avian 

 fauna would be disharmonic were it not for the fact that the archipelago is 

 old enough so that a secondary harmony of its own has had time to develop 



FIG. 13.9. Beak of the 

 warbler finch iCerfhi- 

 dea). (From Lack, Dar- 

 win's Finches, Cam- 

 bridge University Press, 

 1947, p. 57.) 



