FAUNA OF THE ALEUTIAN ISLANDS AND ALASKA PENINSULA 21 



One cannot escape the conviction that if we grant a certain 

 degree of climatic influence on distribution of vegetation to cause 

 it to fall into broad life zones, many of the birds and mammals 

 that have become adapted to vegetation types will also tend to 

 fall into these same life zones. These birds and mammals may be 

 affected to a lesser extent by the life-zone climatic influences than 

 by the indirect effects of these influences — the vegetation type of 

 the habitat. 



It should be kept in mind that, in boreal regions, biotic units 

 are not so clearly defined as in desert or semidesert areas. Griggs 

 (1934c), writing on Arctic vegetation, says, 



In short every feature of Arctic vegetation, the anomalies in the geographi- 

 cal distribution of arctic species, the occurrence of many species in all 

 sorts of habitats, and their apparent indifference to the diverse conditions 

 thereof, the lack of defmiteness to the composition of the plant cover 

 in any particular habitat, the physical instability of the ground itself, the 

 general ruderal character of arctic vegetation, the large number of our 

 weeds which are native to the arctic — all these testify to an instability 

 in arctic vegetation very different from the relatively stable plant forma- 

 tions of the temperate zone. 



He states further that — 



First, combined with the demonstrated active migration of the Alaskan 

 forest into the arctic, it gives definite support to the supposition that vegeta- 

 tion there has not yet recovered from the glacial period but is still in process 

 of active readjustment. 



This statement is applicable to the fauna as well, especially 

 in the Aleutian district. Native rodents have only begun to en- 

 croach on the Aleutian Islands. Savannah sparrows have gone 

 only part way. Song sparrows have reached Attu, but fox spar- 

 rows have gone only as far as Unimak. Foxes had started to 

 enter the Aleutian chain from Alaska, as well as from Siberia, 

 before man intentionally affected their distribution. 



Minute organisms that thrive unusually well in the cold waters 

 of the northern seas have set up a food chain that developed a 

 rich marine biota. This accounts for the presence of the fish, 

 pinnipeds, whales, and sea otters that once inhabited these wa- 

 ters so abundantly. Given such a good supply of food, with an 

 abundance of ideal cliffs and lava beds and boulder beaches for 

 nesting sites, it is logical that the present swarming seabird 

 colonies have assembled in the Aleutians. 



There is much of the Arctic element in the Aleutians. In- 

 deed, the Arctic and Alpine merge on these islands. The moun- 

 tain-loving rosy finches and the Arctic snow bunting nest 

 practically side by side, close to sea level. Alpine vegetation types 



