FAUNA OF THE ALEUTIAN ISLANDS AND ALASKA PENINSULA 17 



since the territory in question was "opened for settlement" ; how- 

 ever, the conclusions submitted are based on strong probability at 

 least. 



It will be seen that the coastal mountain masses of southern 

 Alaska and the Alaska Range form a barrier. Although this is 

 not an absolute barrier, presumably it is enough of an obstacle 

 that the way of least resistance would be north and west along 

 the coast for some species. Similarly, there is an easy avenue 

 southward along the open Bering Sea coast for tundra-loving 

 forms. And the Aleutian chain, reaching out close to Siberia, 

 is an inviting route. 



ENVIRONMENTAL INFLUENCE 



There are some striking environmental influences operative in 

 the Aleutian district. We know, of course, that humid regions 

 tend to produce dark pigmentation, and this fact holds true for 

 this area. The rosy finches reach their darker hues in the Aleu- 

 tian area, with the darkest in the Pribilofs. The fox sparrows 

 show the same tendency, exceeded in dark tones only by the 

 populations of the excessively humid Pacific rain-forest zone that 

 extends from the coast and islands of southeastern Alaska, south- 

 ward to the northwest coast of the United States. Except for 

 the aberrant yellow types in the middle Aleutians, the darkest 

 rock ptarmigans are found in the Aleutian area, especially on 

 Attu and the Commanders. Here, parasitic jaegers are, and the 

 Arctic foxes are, almost entirely in the dark-color phase. In 

 primitive times, silver foxes were unusually plentiful somewhere 

 in this district, judging by the cargoes of the first Russian traders. 

 The lemmings, Dicrostonyx, of Unalaska and Umnak do not ac- 

 quire a white pelage in winter. 



This is also a region of giantism. Note the huge size of the 

 song sparrows, Savannah sparrows, and rosy finches, which, as 

 genera, reach their greatest size in the Aleutians and Commander 

 Islands. Here, the Aleutian winter wrens, as a group, have de- 

 veloped unusually long bills. Here, too, we may include the Alaska 

 brown bear, which achieves its greatest size on the Alaska Penin- 

 sula, Unimak Island, and Kodiak Island. 



Marine biologists have found that in many instances the in- 

 vertebrate subspecies in the northern Pacific waters, and even 

 farther north, are strikingly larger than forms of the same 

 species farther to the south. This invites interesting speculation. 

 As pointed out later, the Aleutian waters are unusually rich in 

 plankton, and there is an abundant and varied marine inverte- 



