FIG. 13.11. Beak of Loxops vi- 

 rens. (After Rothschild; from Ama- 

 don, "Ecology and the evolution 

 of some Hawaiian birds," Evolu- 

 f/on. Vol. 1, 1947.) 



300 INTRODUCTION TO EVOLUTION 



flowers. Obviously such a beak can be used for sucking nectar from short 

 flowers also, yet its sphere of usefulness is definitely restricted. It is used at 

 times for capturing small insects, but it is not good for cracking seeds, or for 

 boring into bark and wood, or for eating fruits. Its possessor is, then, 



highly adapted for one mode of feeding 

 and is likely to remain a successful mem- 

 ber of the fauna only so long as that mode 

 of feeding is open to it. It affords us an 

 example of a high degree of specialization, 

 spelling success so long as the environment 

 remains unchanged but carrying with it 

 the threat of extinction when the environ- 

 ment changes. 



Is there no other way in which the nectar 

 at the base of long, tubular flowers can be 

 reached than by developing a slender, curved beak useless for almost every- 

 thing else? Flowers are not very substantial structures. Why not pierce a 

 hole through the base of the corolla and reach the nectar directly? Bumble- 

 bees do it, why not birds? As a matter of fact Loxops virens (Fig. 13. 11) 

 has been observed to obtain nectar or insects from lobelia blossoms in this 

 manner. Thus this species has 

 achieved the result without sac- 

 rificing what may be termed an 

 "all-purpose" beak. It is proba- 

 bly no accident that members 

 of this species are among the 

 most abundant and widespread 

 of the drepanids, while the pos- 

 sessors of the slender, curved 

 beaks are among the rarest. "It 

 is frequently of greater value to 

 be adaptable than it is to be 

 highly adapted." (Seep. 13.) 



The Family Drepaniidae is 

 divided into two subfamilies. 

 Drepanis belongs to one of 



these. Birds with long, curved beaks are also found in the other subfamily. 

 Hemignathus obscurus is an example (Fig. 13.13). Its beak is believed to 

 have evolved from a shorter, decurved beak such as that possessed by mod- 

 ern Loxops virens (Fig. 13.11). Comparison of the two figures will reveal 



FIG. 13.12. Curved flov/er of the lobelia, C\er- 

 moniia grandiflora. (After Porsch; from Ama- 

 don, "The Hawaiian honeycreepers [Aves, Dre- 

 paniidae]," Bulletin of American Museum of 

 Natural History, Vol. 95, 1950.) 



