444 Cooke, Bird Migration in the Mackenzie Valley. [oct. 



Mountains through Colorado, Wyoming and Central Montana to 

 Western Saskatchewan, over an almost uniform plain 5,000-6,000 

 feet in altitude. Probably some species do follow this route, but 

 no positive proof of this has been found, and it is known that several 

 species for which this would seem to be the most desirable path, 

 actually go many hundred miles out of their way to travel a route 

 farther east. The birds that come into the Rocky Mountains are 

 for the most part birds that are to breed there or to go north only 

 into the southern parts of Canada; very few go even as far north 

 as northern Alberta. Hence in considering the probable routes 

 of migration to the Mackenzie Valley we can ignore the usual north 

 and south direction and consider that the bird comes either from 

 the southeast or the southwest. 



The second route from California to the Mackenzie is the shortest 

 of the three. No deserts or high mountains intervene and the whole 

 country seems well adapted to support a wealth of bird life. If this 

 route was largely used, then the birds of the Mackenzie Valley 

 would be most closely related to the species of the western United 

 States. Since the contrary is the fact, very few migratory western 

 birds occurring in the Mackenzie Valley, it follows that only a few 

 species can use this second route. 



The third route is the longest and seems quite roundabout to one 

 who is in the habit of thinking of migration as always a north and 

 south movement. In the spring most migratory birds enter the 

 United States along the north shore of the Gulf of Mexico between 

 Florida and Texas. Of these the larger part enter in a still smaller 

 path, six hundred miles wide, the middle of which is the mouth of 

 the Mississippi River. At the border of the United Stat^, the 

 course of migration divides: part of the birds travel northeast to 

 New England, the Gulf of St. Lawrence, and to Labrador's inhos- 

 pitable shores; a second part migrate straight north to the Great 

 Lakes and Hudson Bay; the third part move at first north nearly 

 to the northern boundary of the United States and then turn north- 

 west to the valley of the Mackenzie and even to Alaska. This last 

 described route is the principal highway for the migratory birds of 

 the Mackenzie Valley and is the most natural and notable migration 

 route on the whole globe. Stretching for more than three thousand 

 miles from the mouth of the Mississippi to the mouth of the Macken- 



