CHAP. XIII THE GALAPAGOS ISLANDS 283 



Families. Species. Remarks. 



RallidjB. 4. Porzana galapagoensis Rare, loc. unknown. 



5. Hsematopiis galapagoensis ... Albemarle Is. eastward. 



Laridse 6. Anous galapagoensis Albemarle Is. eastward. 



Procellariidfle 7. Oestralata phaeopygia Galapagos Archipelago. 



8. Puffimis subalaris Galapagos Archipelago. 



Spheniscidse 9. Spheniscus mendiculus Albemarle, Charles and 



James Is. 



We have here every gradation of difference from perfect 

 identity with the continental species to genera so distinct 

 that it is difficult to determine with what forms they are 

 most nearly allied ; and it is interesting to note that this 

 diversity bears a distinct relation to the probabilities of, 

 and facilities for, migration to the islands. First, we have 

 the almost cosmopolite short-eared owl (Asio brachyotus), 

 which ranges from China to Ireland, and from Greenland 

 to the Straits of Magellan, and of this the Galapagos bird 

 is probably only one of the numerous slight varieties. 

 The little wood warbler {Dendroeca aureola) is a species 

 which is found also in Ecuador. 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 

 exceptionable 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 conditions of existence 

 under which they have been placed. It is remarkable 

 how often the different species thus formed are confined 

 to one island only. Thus, the eight species of Certhidea 

 each inhabit a single island. The same is the case with 

 seven of the eight thrushes, and with a large proportion 

 of the finches, so that no less than forty-seven out of the 

 sixty-three peculiar land-birds are at present known to 

 inhabit only one island. 



Now all these phenomena are strictly consistent with 



