298 INTRODUCTION TO EVOLUTION 



(p. 283). We have seen that the ancestors of Darwin's finches reached the 

 Galapagos archipelago so early that a wide variety of environmental niches 

 was open to them. The same seems to have been true of the ancestors of 

 the drepanids; it is probable that they were the first land birds to reach the 

 Hawaiian archipelago. In these earlier times the drepanids, Hke Darwin's 

 finches, were relatively free from both enemies and competitors. Thus they 

 spread over all the islands suitable to them and became adapted for a wide 

 variety of foods. As in the case of Darwin's finches, these adaptations must 

 have arisen when available food supply, rather than enemies or competi- 

 tors, formed the important factor tending to limit population size. Thus a 

 premium would have been placed on ability to utilize foods different from 

 those being eaten by the majority of the population. Such an interpretation, 

 at least, gives us a reasonable explanation for the development of the amaz- 

 ing variety of beaks exhibited by the drepanids (Fig. 13.10). 



The beak form believed to be most like that of the ancestral drepanid 

 is possessed today by such a species as Loxops virens (Fig. 13.11). This 

 relatively unspecialized little bird lives largely on nectar and insects ob- 

 tained from the blossoms of flowering trees, such as the ohia. These flowers 

 have short corollas, hence the nectar is easily reached. Berries are also 

 eaten. 



Nectar feeding is believed to have been the original food habit of ances- 

 tral drepanids. Beaks such as those already mentioned are entirely adequate 

 for obtaining nectar from flowers having short corollas, especially when the 

 tongue is tubular, and frayed at the end into a brushlike tip, as is the typi- 

 cal drepanid tongue. The effect is that of being provided with a built-in 

 soda straw. 



A unique group of plants belonging to the Lobelia family developed in 

 Hawaii. Lobelias assume many forms, some herbs, some shrubs, still others 

 small trees. The lobelia blossoms have long, curved, tubular corollas (Fig. 

 13.12). Hence the nectar is relatively inaccessible. Feeding on nectar from 

 these tubular blossoms are found drepanids with one of the most remark- 

 able of the beak adaptations. The extreme form of this adaptation is ex- 

 hibited by the genus Drepanis (Fig. 13.10). Such long, slender, strongly 

 curved beaks are obviously well adapted for reaching the bottom of tubular 

 corollas. The significance of the common name "sicklebill" is readily ap- 

 parent when we look at this form. The foreheads of birds having it are 

 frequently observed to be plastered with the pollen of the lobelia flowers. 

 Thus the visits of the birds aid in the reproduction of these plants. 



Some readers may feel that birds with such slender, sickle-shaped beaks 

 have paid a very high price for ability to reach the bottom of long, tubular 



