ISLAND AVIFAUNAS 191 



only 1 1 are resident, the remainder being abnormal 

 migrants of more or less frequenc3\ Not a single species 

 is endemic. The Galapagos can claim 57 species of 

 birds, and of these no less than 38 are absolutely- 

 endemic, all the land birds (31 in number) being 

 peculiar except one species, and more than half generi- 

 cally so ! 



The facts briefly stated above are very interesting 

 ones, and apparently inexplicable by any known laws 

 of avian dispersal. The anomalies, however, are but 

 apparent, the difficulties of explanation are far more 

 imaginary than real. This very large amount of appar- 

 ently anomalous and unequal dispersion of species over 

 these island areas is probably entirely due to geo- 

 graphical causes, correlated with avian migration. I 

 think it may be safely laid down as a universal rule that 

 islands situated on a direct and important line of Migra- 

 tion are never remarkable for a great or predominant 

 number of endemic species, or even of local races, and it 

 is the exception to find any such peculiar species at all. 

 On the other hand, islands remote from any dominant 

 line of Migration just as invariably contain proportion- 

 ately or absolutely large numbers of endemic species or 

 peculiar races. The islands most remarkable for their 

 number of endemic species are almost without exception 

 situated in the Southern Hemisphere, or within the 

 Tropics, where Migration does not prevail to anything 

 like the extent that it reaches in the Northern Hemi- 

 sphere, and where — as in the Tropics — the climate is one 

 of uniform warmth and stability, rendering migratory 

 movement on any very important scale unnecessary. 

 Briefly, then, we find the great number of endemic or 



