CHAP. XIII THE GALAPAGOS ISLANDS 283 



rano-es over the whole of North America and as far south 

 as New Grenada. It has also been occasionally met with 

 in Bermuda, an indication that it has considerable powers 

 of flight and endurance. The more distinct species — as the 

 tyrant fly-catchers (Pyrocephalus and Myiarchus), the 

 ground-dove (Zenaida), and the buzzard (Buteo), are all 

 allied to non-migratory species peculiar to tropical America, 

 and of a more restricted range ; while the distinct genera 

 are allied to South American groups of thrushes, finches, 

 and sugar-birds which have usually restricted ranges, and 

 whose habits are such as not to render them likely to be 

 carried out to sea. The remote ancestral forms of these 

 birds which, owing to some exceptional causes, reached the 

 Galapagos, have thus remained uninfluenced by later 

 migrations, and have, in consequence, been developed into 

 a variety of distinct types adapted to the peculiar con- 

 ditions of existence under which they have been placed. 

 Sometimes the different species thus formed are confined 

 to one or two of the islands only, as the three species of 

 Certhidea, which are divided between the islands but do 

 not appear ever to occur together. Nesomimus imrvulus is 

 confined to Albemarle Island, and N. trifascieitus to Charles 

 Island ; Ccictornis iKillida to Indefatigable Island, C. 

 Irevirostris to Chatham Island, and C. ahingcloni to 

 Abingdon Island. 



Now all these phenomena are strictly consistent with 

 the theory of the peopling of the islands by accidental 

 migrations, if we only allow them to have existed for a 

 sufficiently long period ; and the fact that volcanic action 

 has ceased on many of the islands, as well as their great 

 extent, would certainly indicate a considerable antiquity. 



The great difference presented by the birds of these 

 islands as compared with those of the equally remote 

 Azores and Bermudas, is sufficiently explained by the 

 difference of climatal conditions. At the Galapagos there 

 are none of those periodic storms, gales, and hurricanes 

 which prevail in the North Atlantic, and which every 

 year carry some straggling birds of Europe or North 

 America to the former islands ; while, at the same time, 

 the majority of the tropical American birds are non- 



