122 Allen, Origin and Distribution of N. A. Birds. [April 



Before proceeding to consider the North American Region and 

 its faunal subdivisions, a few words may be devoted to the Ameri- 

 can Arctic, which is here set off' from the rest of North America 

 as a part of the Arctic Realm. If North America were entirely 

 isolated from the rest of the world, it would be quite proper to treat 

 the American Arctic as merely a subdivision of the North Ameri- 

 can Region ; but in view of the fact that it is in reality a part of a 

 homogeneous hyperborean fauna of circumpolar distribution, it 

 seems more in accordance with general facts to consider it as 

 forming part of an Arctic Realm. The propriety of this seems 

 especially emphasized when we consider that (to quote the words 

 of Dr. Merriam) •'■the animals and plants inhabiting the Arctic 

 regions are usually specifically identical throughout Arctic 

 America, Greenland, and the polar parts of Eurasia and outlying 

 islands," "the types inhabiting the Arctic Zone being few in num- 

 ber and uniform in character throughout their distribution." 1 The 

 fauna of this Arctic Zone is thus no more American than it is 

 Eurasiatic, and differs far more from that of the adjoining region 

 to the southward, both in North America and Eurasia, than does 

 the American Arctic from the Eurasian Arctic. The Arctic 

 Realm possesses only a small number of peculiar types in.propor- 

 tion to its area or in comparison with the other realms, yet its 

 ratio of peculiar types, in comparison with its meagre fauna, is 

 by no means low. It seems an eminently natural division from 

 the fact that its southern boundary marks the termination of forest 

 vegetation, with which necessarily stop all the mammals, birds 

 and insects which depend upon forests for food, shelter and a 

 congenial home. Of the 65 genera of birds occurring in the 

 American Arctic 60 are, as already shown, circumpolar, and 

 5 are American water birds that reach it for a short stay during 

 the breeding season. 



The American Arctic may be divided into two areas which 

 may take the rank of faunas, namely: (1) Barren Ground, (2) 

 A/askan- Arctic. The last has been characterized by Mr. E. 

 \V. Nelson, 2 and the first by me in a recently published paper on 

 'The Distribution of North American Mammals' (1. c. p. 220). 



1 Proc. Biol. Soc. Wash., VII, 1892, pp. 39, 40. 



2 Rep. Nat. Hist. Coll. in Alaska, 1887, pp. 26-32. 



