MIGRATION AND ORIGINS 271 



Main Paths of Migration 



By utilizing as indicators of migratory paths the differentiation 

 of races, direction of observed migration and a few significant re- 

 corded dates of migration on the approaches to the northern nesting 

 grounds, I have assigned 93 of the species nesting in northern Alaska 

 and Yukon to migratory paths in North America, over the Pacific, 

 and in Asia. The majority of these migrations pass through western 

 Canada and along American Pacific coasts, and only 22 of these 

 species appear to migrate east of the Eocky Mountains. The totals 

 from tables 10 and 11 are summarized below : 



Along American Pacific coasts 36 



Through western Canada 25 

 Rocky Mountains to the Mississippi 17 



East of the Mississippi 5 



To Asia 5 



Over Pacific Ocean 2 



In Alaska 3 



Total 93 



Without this analysis I would have subscribed to Dixon's (1938, p. 5) 

 comment on the birds of Mount McKinley Park, Alaska, a fauna 

 similar to that of northern Alaska, "a large proportion of the breeding 

 birds of the McKinley regions consist of eastern forms." As it is, 

 I do not. 



The designation of birds as western or eastern American depends 

 on the location assigned to the geographical boundary between east 

 and west, and to whether the reference is to species or race. It is 

 further influenced by whether current distribution or the origin of 

 the form is meant. The present development of taxonomy, geograph- 

 ical distribution, and recent climatic history are leading to the assign- 

 ment of each taxonomic form to a meaningful position in time and 

 space. 



The migration of 22 species of birds through North America east 

 of the Eocky Mountains into northwestern Alaska and Yukon is im- 

 pressive. In his explorational travels in the Yukon Valley, W. H. 

 Dall (1870, p. 288) detected the eastern character in the fauna north 

 of the Alaska Eange, and remarked upon the common distribution 

 of North American pike {Esox lucius) in the Yukon Eiver as far 

 west as tidewater as an indication of a nearly continuous connection 

 by water between northern Alaska and the interior of North America. 

 By recognizing an extensive fauna in Alaska related to that of the 

 interior of Canada, Dall concluded that the northern mountains 

 were readily traversed by birds migrating to Alaska. In his great 

 study of the fauna of northern North America, Sir John Eichardson 



