The southward route of those migratory landbirds of the Pacific area that leave the United States in winter extends chiefly through the interior of California to the mouth of the Colorado River and on to winter quarters in western Mexico (Fig. 18, routes 6 and 7).
[Illustration: _Figure 21. The breeding range, wintering range, and main migration route of Ross' geese. This is the only species of which practically all members breed in the Arctic, migrate south through the Canadian prairie, and upon reaching the United States, turn to the southwest rather than the southeast. The southern part of this route, however, is followed by some mallards, pintails, wigeons, and other ducks._]
[Illustration: _Figure 22. Breeding and wintering ranges of the western tanager. See Fig. 23 for the spring route taken by the birds breeding in the northern part of the range._]
The movements of the western tanager 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 northern British Columbia and southwestern Mackenzie. Its winter range is in two discontinuous areas--southern Baja California and eastern and southwestern Mexico south to Guatemala (Fig. 22). During spring migration the birds appear first in western Texas and the southern parts of New Mexico and Arizona about April 20 (Fig. 23). By April 30 the vanguard has advanced evenly to an approximate east-west line across central New Mexico, Arizona, and southern California. By May 10 the easternmost birds have advanced only to southern Colorado, while those in the far west have reached northern Washington. 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 those present in Alberta on that date, instead of traveling northward through the Rocky Mountains, their summer home, actually reached there by a route that carried them west of the Rockies to southern British Columbia and thence eastward across the still snowy northern Rocky Mountains.