Vol. XXXIIl 



1911 



j Cooke, Bird Migration in the Mackenzie Valley. ^ol 



ranging to the eastern edge of the plains in the United States are: 

 Larus ealifornieus, Branta canadensis hutchinsi, Grus canadensis, 

 Macrorhamphus griscus scolopaceus, Sayornis sayus, Xanthoccphalus 

 xanthoccphalus, Calcarius lapponicus alascensis, Calcarius pictus, 

 Pocccetcs gram incus confinis, Passcreulus sandwichensis alaudinus, 

 Passer hcrbulus leeontei, Zonotrichia leucophrys gambcli, Spizella 

 monticola ochracca, Spizella pallida, and Sciurus noveboracensis 

 notabilis. 



Larus ealifornieus winters abundantly on the coast of British 

 Columbia and breeds commonly from Great Slave Lake northward, 

 showing that its route of migration is northeast across British 

 Columbia. 



Branta canadensis hutchinsi is known to migrate in immense 

 flocks from the plains of the Mississippi to those of the Mackenzie 

 on its way to its northwestern breeding grounds. The same is true 

 of Macrorhamphus scolopaceus, the line of whose northwestern mi- 

 gration is known to extend from Florida to Great Slave Lake; the 

 same route is undoubtedly followed by Grus canadensis. 



The earliest individuals of Sayornis sayus reach southern British 

 Columbia about two weeks earlier than the first arrive in southern 

 Colorado. The Alberta dates agree with those of Montana rather 

 than those of British Columbia and Washington, while the dates 

 on the lower Mackenzie and the Yukon can be satisfactorily ex- 

 plained only on the supposition that these birds have come from 

 British Columbia. Xanthocephedus xanthocephalus is so rare at 

 Athabaska Lake and northward, that it can be considered as hardly 

 more than a straggler in the Mackenzie Valley. The date of arrival 

 in eastern Saskatchewan however is so much earlier than in eastern 

 Montana, as to indicate that the birds of Saskatchewan come from 

 the southeast. The migration records of Zonotrichia leucophrys 

 gambeli are so much earlier in British Columbia and Alaska than 

 in corresponding latitudes to the eastward as to make it practically 

 certain that the Alaska birds have come by way of the interior 

 warm valleys of British Columbia. Hence it is equally probable 

 that the individuals which swarm in Nebraska, Kansas, and south- 

 ward during migration and winter are the birds that pass north 

 through Manitoba and Saskatchewan to breed in the Mackenzie 

 Vallev. 



