168 U. S. NATIONAL MUSEUM BULLETIN 217 



eastern Mackenzie and Keewatin, which extend over the Barren 

 Grounds and the pre-Cambrian shield, are not mountainous, in contrast 

 with the rugged terrain of Yukon and Alaska. There are thus changes 

 in the general climatic, geological, and vegetational conditions to 

 correspond with the northern limit of nesting. 



Among 28 migratory species of North American ducks only three 

 are now divided into races (A. O. U., Check-list, 1957) : the blue- 

 winged teal, with an Atlantic race of separate range; the common 

 eider, in which the maritime nesting range of the species is easily 

 separable into separate ranges for each race; and the white- winged 

 scoter, the races of which winter in widely separated maritime ranges 

 on either side of the continent. 



White-winged scoters and the five other species of ducks most 

 common in migration at Old Crow showed the trend of their flights 

 to be eastward along the Porcupine in spring. On account of their- 

 western wintering location, goldeneyes (BucepTidla) are also suspected 

 of migrating eastward. About 100 miles east of Old Crow the Eich- 

 ardson Mountains bound Mackenzie and Yukon, but they are low 

 and provided with short passes between the easternmost marshes of 

 the Porcupine Valley and the western marshes of the Mackenzie 

 Valley. The eastward trend of migratory ducks on the Porcupine 

 appears strong enough to lead them to contact with or even to inter- 

 mingling with, the populations migrating and nesting in the northern 

 Mackenzie Valley. 



In addition to the six species observed and one estimated to migrate 

 eastward to make contact with the ducks nesting in Mackenzie, lesser 

 scaups nest so numerously along Porcupine Valley that their breed- 

 ing area is continuous from Alaska to Mackenzie. Greater scaups were 

 not recorded from southern Yukon (Rand, 1946), and we are not sure 

 of their abundance along the Porcupine Valley. But some are there 

 in summer and the Alaskan breeding birds are connected with the 

 Mackenzie nesting ground by at least a scattered nesting population 

 in a narrow band through northern interior Yukon. Barrow's golden- 

 eyes are now known from all over Yukon south of the Arctic coast, 

 but American goldeneyes, like greater scaups, appear to form the 

 connection between Alaska and Mackenzie only in the north along 

 Porcupine Valley. 



All the observed trends in migration of ducks at Old Crow were 

 eastward, and on grounds of propinquity the Alaska and northern 

 Yukon nesting ducks are suspected of arriving in spring from the 

 western parts of their wintering grounds. Spring migration and 

 nesting appear to separate, although not to isolate the far northwestern 

 population genetically so as to form geographic races. Only two 

 species of ducks are acceptably differentiated as races and therefore, 



