1915 J Cooke, Bird Migration in the Mackenzie Valley. 449 



and occurs in migration in Colorado and Wyoming, but the indi- 

 viduals that appear first in Alberta are not birds that have passed 

 through Colorado, Wyoming and Montana, because the dates of 

 migration, as indicated on the map, show that migration is early 

 and rapid in the middle Mississippi Valley and late and slow along 

 the foothills of the Rocky Mountains. The earliest arrivals in 

 southeastern Saskatchewan appear on the average May 17, but 

 they do not come from directly south, since in eastern Colorado, 

 600 miles to the southward the birds do not appear on the average 

 until May 22. The first advance to Athabasca Lake by May 28, 

 which is just the date at whi :h they appear on the average in north- 

 ern Montana and northern Idaho. Therefore it is evident that 

 the birds of the Mackenzie Valley at Lake Athabaska have not 

 come by way of the Rocky Mountains, but by the route near the 

 Mississippi River. 



The same general method of proof can be applied to the migra- 

 tions of the other seventeen species in this group. The proof is 

 particularly clear and convincing in the case of the Robin, Flicker, 

 Bronzed Grackle, Redstart and the Black-poll, Tennessee and 

 Black-and-White Warblers. 



Eighty-two other species of migratory birds breed in the Macken- 

 zie Valley and during the winter or in migration occur across the 

 United States from the Atlantic to the Pacific. But even with 

 these species it can be shown that most of them probably reach the 

 Mackenzie Valley from the middle part of the Mississippi Valley. 

 These eighty-two may be divided into fifty-eight species of wide 

 ranging water birds, nine species of hawks and owls, and fifteen 

 species of smaller land birds. 



The fifty-eight species of water birds that are found at Lake Atha- 

 baska and which also range from the Atlantic to the Pacific oceans 

 present a problem with regard to their route of migration that with 

 the records at hand cannot be certainly solved. The Canada Goose 

 is one of the abundant water birds of the Mackenzie Valley and 

 may be taken as representative of the above mentioned group. The 

 great bulk of' the Mackenzie Valley Canada Geese must come from 

 the Mississippi Valley, where the species is abundant, for Branla 

 canadensis is rather rare on the Pacific coast, its place there and in 

 Alaska being taken largely by the other three forms, hutchinsi, 

 ■occidentalis and minima. 



