1922] Swarth: Birds and Mammals of the Stikine Region 149 



Thus there are certain species of birds and mammals for which 

 the valley of the Stikine Eiver acts as a channel of communication 

 between interior and coast. There are none to which it acts in the 

 opposite role, as a barrier to farther distribution, north or south. It 

 would not to birds, of course, in any event. As regards mammals, 

 conditions here are very different from what, for example, they are in 

 the valley of a stream like the Colorado River, of the southwestern 

 United States. In that region, not only the river itself but also the 

 wide strips of adjacent bottom lands absolutely prevent the passage of 

 certain desert mammals, so that there are a number of species and 

 subspecies restricted to one side or the other (cf. Grinnell, 1914). 



In the Stikine Valley no local conditions ("associations") exist 

 that tend to keep certain groups of animals either close to or far dis- 

 tant from the river banks, and the same forms range unhindered from 

 the water's edge well up the mountain sides. For a period of months 

 the river is frozen over quite to its mouth, and there is no doubt that 

 at that season individuals of many species of mammals cross from one 

 side to the other. 



ZONAL AND FAUNAL POSITION OF THE STIKINE VALLEY 



The Sitkan district of southeastern Alaska has been generally 

 considered to be mostly of the Canadian life zone. The areas that 

 extend above timber on the higher mountains afford a strip of Alpine 

 Arctic of considerable extent, and a drawback to the recognition of 

 the lower altitudes as Canadian is the absence of any well defined 

 intervening strip of Hudsonian. Some birds and mammals that occur 

 elsewhere in the Canadian zone do occur in the lowlands of the Sitkan 

 district, but on the other hand species generally regarded as indicative 

 of the Hudsonian zone are found throughout the whole region. Alto- 

 gether it seems as though all the Sitkan district below Alpine-Arctic 

 should be considered as of the Hudsonian zone, with a strong infusion 

 of Canadian in the southern part at least. Certainly this coastal strip 

 is of a higher life zone than the adjacent interior. 



In the country immediately east of the Coast Range there has not 

 been sufficient work to permit detailed mapping of the life zones. The 

 most recent zonal map covering that section is the one published in 

 the A. 0. U. Check-List (1910, pi. 1) and is on too small a scale to 

 permit of much detail. On that map the Hudsonian zone covers 

 practically all of northern British Columbia, extending considerably 

 farther southward there than in southern Alaska, to the westward, or 



