334 University of California Publications in Zoology [ VOL - 16 



guished six life-zones which he called respectively the Arctic-alpine 

 zone, the Subalpine or Timberline zone, the (Central) Hudsonian or 

 Spruce zone, the (Central) Canadian or Douglas Fir zone, the Neutral 

 or Transition zone, and the Upper Sonoran zone. 



The faunal divisions of eastern North America generally recognized 

 by students of distribution, particularly by ornithologists, at the time 

 Merriam began his work on correlation, were eight in number. Pass- 

 ing from north to south these divisions were (1) Arctic, (2) Hud- 

 sonian, (3) Canadian, (4) Alleghanian, (5) Carolinian, (6) Louis- 

 ianian, (7) Floridian, and (8) Antillean (Merriam, 1890, p. 18). 



Merriam (1890, p. 18) was much impressed with the similarities 

 between the zones of the higher parts of San Francisco Mountain and 

 the faunal areas of northeastern North America and states that 



in many instances, the zones of the mountain may be recognized by the identical 

 species which characterize them in New England and Canada. In short it was 

 found that the faunal and floral zones which go to make up the Boreal province 

 in the East may be traced in a northwesterly direction around the northern end 

 of the Plains of the Saskatchewan, and then south along the sides of the Rocky 

 Mountains even to this isolated peak in Arizona. 



Merriam (1892, p. 22) later extended the correlation of the zones 

 of the eastern and western United States and stated "with some con- 

 fidence" that the Transition zone of the mountains of the West is the 

 equivalent of the Alleghenian of the East and also that the Upper 

 Sonoran is the equivalent of the Carolinian, and the Lower Sonoran of 

 the Austroriparian. He thought that these life-zones followed "the 

 lines of equal temperature during the season of reproduction," and 

 based the correlation mainly on that factor. 



Since that time members of the United States Bureau of Biological 

 Survey and others have extensively followed the life-zone method in 

 describing distribution in North America. A brief statement of the 

 birds and mammals characteristic of each life-zone was published by 

 Merriam in 1898. As used as present, the Timberline zone originally 

 recognized by Merriam has been merged into the Hudsonian zone, but 

 no other important modification has been made. 



Each of the life-zones of the Sonoran region is divisible into two 

 or more faunal areas (Merriam, 1898, pp. 20-49). These faunal 

 divisions are based upon differences in the atmospheric humidity in 

 different parts of the same life-zone (Grinnell and Swarth, 1913, p. 

 217). In California a considerable number of these faunas have been 

 distinguished by Grinnell (1902, p. 7). 



