OF ISLAND FAUNAS 147 



obtained in the islands, and of these forty-one, or con- 

 siderably more than half, are pecuhar to the islands, 

 not being found elsewhere. Most of those which are 

 not peculiar are birds with considerable powers of 

 flight, capable of travelling great distances.' Of the 

 true land birds all but one are pecuhar, and this one 

 is the common rice-bird {Dolichonyx oryzivorus), which 

 occurs throughout the whole of the American continent. 

 This bird is markedly migratory, spending its winters 

 in the West Indies and Central America, and travelling 

 northwards in vast numbers to breed and spend the 

 summer in the northern United States and Canada. 

 There is, therefore, nothing improbable in the supposi- 

 tion that stragglers from the migrating flocks reach 

 the Galapagos Islands from time to time, and so pre- 

 vent an island type from estabhshing itself. The other 

 land birds of the islands show, as Wallace points out, 

 all gradations from close resemblance to forms occurring 

 elsewhere to generic difference. Thus the archipelago 

 contains a special owl — Asio galapagensis — ^but this is 

 very nearly related to the widely distributed short- 

 eared owl {Asio hrachyotus). On the other hand, among 

 the finches pecuhar genera occur, e. g. Geospiza, related 

 to genera of restricted range foimd on the continent 

 of South America. Again, though the islands are 

 relatively so near together, a peculiar genus may be 

 represented by three different species on as many 

 different islands. This is well exemphfied in the case 

 of the honey-creepers of the genus Certhidea, the three 

 species of which occur on different islands. 



The reptiles of the islands are especially remarkable. 

 The giant tortoises have long been famous, and give 

 the islands their Spanish name. Such giant tortoises 

 occur only on islands, being foimd in certain islands in 



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