276 IT. S. NATIONAL MUSEUM BULLETIN 217 



A spectacular phenomenon of arctic life is seen in the eastbound 

 flights of four species of eider ducks along the coast in spring at 

 Barrow. King eiders outnumber all other species and move in such 

 close sequence of large flocks as to exceed any migration I have 

 seen. Sir Hubert Wilkins remarked to me that they constitute the 

 most impressive sight of migratory movement in the world. At the 

 same time gulls {Larus hyperboreus and occasionally Rissa tridactyla 

 and Xema sdbini) move eastward, but in much smaller numbers. The 

 flights of loons, geese, ducks, and shorebirds, while sometimes numer- 

 ous, are irregular, so that they do not compare with the flights of 

 eiders as orderly migratory phenomena. 



From reports originating on the eastern arctic coast of Alaska I 

 gain the impression that the orderly movement of king eiders con- 

 tinues an easterly migration far beyond Alaska. For other birds the 

 eastern arctic coast of Alaska does not seem to be an important 

 migratory route. 



There are no reports known to me which indicate that spring 

 migration passes westward from Mackenzie to the arctic coast of 

 Alaska. The short list of the avifauna on the eastern Arctic coast 

 of Alaska suggests that the region is a terminus for the migration 

 of only a few land birds. The evidence available suggests that some 

 of the land birds arrive there after crossing near the center of the 

 Brooks Range and flying eastward down the Colville Valley. 



The migratory movements of birds in northwestern America can be 

 represented by a diagram (fig. 8) showing the main trend of the sev- 

 eral migratory routes which have been described. For the movements 

 pursued in arctic Alaska and Yukon the evidence is rather clear, but 

 the other migratory routes referred to are at present hypothetical. 

 We thus have the courses of migration delineated with greatest cer- 

 tainty near their arctic terminus and through a country commonly 

 regarded as little known. There an orderly pattern appears which 

 can be easily distinguished because the migratory populations are 

 homogeneous at the time of their proximity to their nesting grounds. 

 These orderly currents of migration are related to such major topo- 

 graphic features as the Eocky Mountains, the Yukon Valley, the 

 Brooks Range, the Bering and Arctic coasts along with their asso- 

 ciated influences upon weather and climate. 



Migration, the Climate, and Taxonomic Differentiation 



I have pointed out a number of distinctions in the races of birds in 

 northern Alaska and Yukon: all resident species restricted to the 

 area form taxonomic races (table 8) , and of the 19 migratory species 

 principally nesting in the area, 14 form American taxonomic races 



