52 CIRCULAR 363, U. S. DEPARTMENT OF AGRICULTURE 
that-appear to characterize the flight of those from the eastern part 
of the continent (fig. 15). 
ARCTIC ROUTES 
In the discussion of the migration of the Arctic tern (p. 31) it was 
noted that this species makes a very distinct west-to-east movement 
across northern. Canada, continning the flight eastward across the 
Atlantic Ocean toward t the western coast of Europe. It seems likely 
that there are other species, including the parasitic jaeger (Stercorarius 
parasiticus) that regularly breed in the northern part of the Western 
Hemisphere but migrate back to the Old World for their winter 
sojourn. Some others, as the red-legged kittiwake (Rissa brevirostris) 
and Ross’s gull (Rhodostethia rosea), remain near the Arctic region 
throughout the year, retreating southward in winter only a few 
hundred miles. The emperor goose (Philacte canagica) in winter is 
found only a relatively short distance south of its breeding grounds, 
and eider ducks (Somateria and Arctonetta), although wintering in 
latitudes well south of the breeding grounds, nevertheless remain 
farther north than do the majority of other species of ducks (fig. 21). 
The routes followed by these birds are chiefly coastwise, and in the 
final analysis may be considered as being tributary either to the 
Atlantic or to the Pacific coast routes. The passage of gulls, ducks, 
and other water birds at Point Barrow, Alaska, and at other points 
on the Arctic coast, has been noted by several observers, and from 
present knowledge it may be said that the best defined Arctic route 
in North America is the one that follows around the coast of Alaska. 
EVOLUTION OF MIGRATION ROUTES 
From the foregoing descriptions of migration routes it will be 
observed that the general trend of migration in most species of North 
American birds is northwest and southeast. It is comparatively 
easy to trace the probable steps in the evolution of the migrations 
of some species, and some routes have developed so recently that they 
still plainly show their origin. 
The tendency is for eastern species to extend their ranges by push- 
ing westward, particularly in the north. For example in the Stikine 
River Valley of northern British Columbia and southwestern Alaska 
the eastern nighthawk (Chordeiles minor minor), eastern chipping 
sparrow (Spizella passerina passerina), rusty blackbird (Huphagus 
carolinus), eastern yellow warbler (Dendroica aestiva aestiva), redstart, 
and others have established breeding stations at points 20 to 100 miles 
from the Pacific Ocean. The robin, flicker (Colaptes auratus), 
slate-colored junco (Junco hyemalis hyemalis), blackpoll warbler, 
myrtle warbler (Dendroica coronata), and ovenbird (Sevwrus auro- 
capillus), all common eastern species, also are established as breed- 
ing birds in western Alaska, the ovenbird having been detected on 
the lower Yukon River. These birds, however, do not migrate in 
fall by any of the Pacific routes, but instead retrace their journey 
across the mountains and move southward along the broad flyways 
of the interior. 
The red-eyed vireo (Vireo olwwaceus), a striking example of an 
obundant woodland bird, is essentially an inhabitant of States east 
af the Great Plains, but an arm of its breeding range extends north- 
