xviii. 9 DARWIN'S FINCHES 527 



Pitiaroloxias, the Cocos-finch, found on Cocos Island 600 miles away, 

 and also having warbler-like characteristics. 



These birds provide a remarkable example of adaptive radiation 

 'with seed-eaters, fruit-eaters, cactus-feeders, wood-borers and eaters 

 of small insects. Some feed on the ground, others in the trees — 



(i) Seeds 



(ii) Seeds 



(Hi) Seeds 



(iv) Leaves 



(vii) Insects, buds 



(v) Seeds, Cactus flowers 

 & Fruit 



(vi) Buds, Fruit 



( vi/i J Insects, buds 



fix) Insects in wood 



fx) Insects in wood (xi) Small so Fc insects (xii) Small soft insects 



Fig. 313. Beaks of Darwin's finches. 



(i) Geospiza magnirostris; (ii) Geospiza fortis; (iii) Geospiza fuliginosa; (iv) Geospiza difficilis 



debilirostris; (v) Geospiza scandens; (vi) Camarhynchus crassirostris; (vii) Camarhynchus psit- 



tacula; (viii) Camarhynchus parvulus; (ix) Camarhynchus pallidus; (x) Camarhynchus helio- 



bates; (xi) Certhidea olivacea; (xii) Pitiaroloxias inornata. (After Swarth, from Lack.) 



originally finch-like, they have become like tits, like woodpeckers and 

 like warblers' (Lack). This is interesting enough, but more can be 

 learned from this extraordinary natural experiment than from other 

 examples of adaptive radiation. Another most striking feature is that 

 the birds are very variable, and are by no means uniformly distributed 

 over the islands. The outlying islands lack certain species and their 

 place is then taken by variants of others, with corresponding modifica- 

 tion of the beak. In some such cases the local subspecies can be clearly 

 seen to have an adaptive significance, but this is by no means always 

 so. Some races found on one or more islands differ in minor features 



