THE MIGRATION OF NORTH AMERICAN BIRDS 49 
on the Oregon-California line, and in the Sacramento Valley of Cali- 
fornia, though a few push on to the San Joaquin Valley. 
A tributary of this flyway is followed by Ross’s goose (Chen 
rosst), which is believed to breed on the Arctic islands north of 
Mackenzie (fig. 24). Its fall migration is across the barren grounds 
to Great Slave and Athabaska Lakes, where it joins thousands of other 
waterfowl bound for their winter homes along the eastern coast of the 
United States and the Gulf of Mexico. But when Ross’s geese have 
traveled south approximately to the northern boundary of Montana, 
they separate from their companions, and turning to the southwest 
cross the Rocky Mountains and settle for the winter in California. 
The route taken by the white-winged scoters that winter on the 
Atlantic coast already has been indicated (p. 43). Some birds of 
this species, however, winter on the Pacific coast from Puget Sound 
south to southern California. Their passage by thousands up and 
down the coast has been noted as far north as northwestern British 
Columbia. The species is known to nest in Alaska, which may be 
the home of some at least of the scoters that winter on the Pacific 
coast. If such be the case, however, it must be admitted that a part 
of the route taken by the birds when on migration is unknown, 
though very few observations are available from the interior of 
northern British Columbia, across which the route may lie. 
The southward route of those migratory land birds of the Pacific 
coast that in winter leave the United States extends chiefly through 
the interior of California to the mouth of the Colorado River and on 
to winter quarters in western Mexico. 
The movements of the western tanager (Piranga ludoviciana) show 
a migration route that is in some ways remarkable. The species 
breeds in the mountains from the northern part of Baja California 
and western Texas north to northeastern British Columbia and 
southwestern Mackenzie. Its winter range is in two discontinuous 
areas—southern Baja California and eastern Mexico south to 
Guatemala (fig. 25). On the spring migration the birds enter the 
United States about April 20, appearing first in western Texas and 
the southern parts of New Mexico and Arizona (fig. 26). By April 
30 the van has advanced evenly to an approximate east-and-west line 
across central New Mexico, Arizona, and southern California. But 
by May 10 the easternmost birds have advanced only to southern 
Colorado, while those in the far West have reached northern Wash- 
ington. Ten days later the northward advance of the species is 
shown as a great curve, extending northeastward from Vancouver 
Island to central Alberta and thence southeastward to northern 
Colorado. Since these tanagers do not reach northern Colorado until 
May 20, it is evident that those present in Alberta on that date, 
instead of traveling northward through the Rocky Mountains, which 
from the location of their summer and winter homes would seem to 
be the natural route, reached there by the Pacific coast route to south- 
ern British Columbia and thence across the mountains, despite the 
fact that these are still partly covered with snow at that time. 
PACIFIC OCEANIC ROUTE 
The route of the Pacific golden plover (Pluvialis dominica fulva) is 
fully as interesting and as remarkable as the elliptical course followed 
by its eastern cousin (P. d. dominica) (fig. 22). The breeding range 
