526 EVOLUTION OF BIRDS xvm.9 



reckoned to belong to fourteen species, classed in four genera (Fig. 

 312), one of these being found on the distant Cocos Island. 



Evidently these finches have been in the archipelago for a consider- 

 able time and the specially interesting feature is that not only have 

 they formed races recognizably distinct, but they have radiated to 

 form a series of birds that have quite varied habits, many of them 

 very un-finchlike. The main differences are in the form of the beak, 

 which varies greatly with the food habits (Fig. 313). The central 



C pan id us 



|woodpecker-like| 

 C heliobates 



G magnirostns 

 6 Fortis 



6 scandens 



C.psittacula 

 C pauper 

 C. parvu/us 



Cxrassirostns 



PINAROIOXIAS 

 inornata 



FRINGILLiD 

 ANCESTOR 



Fig. 312. Suggested evolutionary tree of Darwin's finches. (From Lack.) 



species, which are also the nearest to the presumed Fringillid ancestor, 

 are the ground-finches, Geospiza, of which there are five species, 

 feeding mainly on seeds. Two further species of Geospiza have left 

 the ground and taken to eating cactus plants. The tree-finches, placed 

 in a distinct genus Camarhynchns, include one vegetarian and five 

 mainly insectivorous species, one of the latter, C. paiiidus, having 

 acquired the habit of climbing up the trees like a woodpecker and 

 excavating insects with a stick (Fig. 280). A third group of this 

 remarkable subfamily has acquired a convergent likeness to warblers : 

 Certhidea has a long slender beak and eats small soft insects ; by many 

 it has been regarded as distinct from the other Galapagos finches, but 

 it has now been shown to resemble them, not only in structure but 

 also in breeding-habits. Nevertheless it probably diverged some time 

 ago and is found on all the islands. Presumably its success is due to 

 the absence of other warbler-like birds, since the true Galapagos 

 warbler is a recent arrival. The fourth genus of the Geospizinae is 



