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



along the mountains of eastern British Columbia to the valley of 

 the Liard and reaches the Mackenzie a few* miles below Fort Simp- 

 son. 



The relation of the breeding and wintering areas of the Short- 

 billed Gull makes it probable that the main migration route follows 

 up the Fraser River and down the Peace River to the breeding 

 grounds on Great Slave Lake and northward. 



The Black Brant is a common breeder at the mouth of the Mac- 

 kenzie and along the coast to the eastward. It does not reach 

 Mackenzie from the south, indeed it is not known inland in that 

 Province, but in spring migration it passes up the Pacific coast to 

 the mouth of the Yukon, up this river to its junction with the Por- 

 cupine, and up this stream and across the low* divide to the mouth 

 of the Mackenzie. It seems probable that the Pacific Loon (Gavia 

 pacifica) and the Sabine Gull (Xema sabini) follow this same route, 

 but the proof is^ot as yet conclusive. 



The Pacific Eider (Somateria V-nigra) does not occur inland in 

 either Alaska or Mackenzie. It winters around the Aleutian 

 Islands and is a common breeder on the coast east of the mouth of 

 the Mackenzie. Hence it follows that the line of migration must 

 pass through Bering Strait and go round the northern coast of 

 Alaska. It seems certain that the King Eiders (Somateria specta- 

 bilis) and the Glaucous Gulls (Larus hyperboreus) breeding on the 

 Mackenzie coast arrive by the same route rather than from the 

 Atlantic side. Indeed it can be said there is nothing to indicate 

 that any birds migrate regularly from the Labrador coast north- 

 westerly to the coast of western Mackenzie. 



A migration route as yet unsolved is that of the Yellow-billed Loon 

 (Gavia adamsi). It appears at Great Slave Lake as soon as any 

 part of the lake is open. It is not known at any time of the year, 

 either east, south, or west of Great Slave Lake, and at the time it 

 appears there, no open water exists anywhere between that Lake 

 and the Arctic Ocean, and the species is not yet recorded from any- 

 where inland in Alaska. In fact the records as they stand at 

 present are explainable only on the theory of a single flight from the 

 open Polar Sea to the summer home on Great Slave Lake, and 

 such a flight is scarcely believable. 



The three western species occurring in the Mackenzie Valley 



