GEOGRAPHIC DISTRIBUTION OF ANIMALS: OCEANIC ISLANDS 



301 



that the principal evolutionary change was elongation. The beak of Hemi- 

 gnathiis obscurus is used mainly for probing bark cavities in search of the 

 insects which form the principal article of diet. But the beak is also used 



FIG. 13.13. Beak of Hemignafhus obscurus. (After Roths- 

 child; from Amadon, "Ecology and the evolution of some 

 Hawaiian birds," Evolufion, Vol. 1, 1947.) 



at times for obtaining nectar from the tubular blossoms of lobelias. Ama- 

 don (1950) suggested that the long, curved beaks of Drepanis and Hemi- 

 gnathus form an example of parallel evolution, the beak of Drepanis having 



FIG. 13.14. Beak of Hemignafhus lucidus. (After 

 Rothschild; from Amadon, "Ecology and the evolu- 

 tion of some Hawaiian birds," Evolution, Vol. 1, 

 1947.) 



evolved as an adaptation for the obtaining of nectar from long, tubular 

 flowers, while the beak of Hemignathus evolved as a forcepslike device for 

 probing after insects living in bark cavities. 



