Page:Land Birds of the Pacific District (1890).djvu/13

Rh therefore, unsatisfactory. It will, however, be preserved for future use. All persons are credited with the data which they contributed to the report, which has been simply a labor of love from beginning to end.

In California the spring migrating land birds almost invariably come gradually and almost imperceptibly, probably many arriving in the night or early morning; and I have never seen, on the Pacific Coast, what might properly be termed a "bird wave," except upon one occasion, and that was in the spring of 1866, before I began to keep a record of bird movements. Mr. F. Stephens noticed a "bird wave" at Canipo, San Diego County, the last of April, 1877 (Bull. Nutt. Orn. Club, July, 1883, p. 188). Except these, I know of no other occurrences of this kind on this Coast, of course excluding the occasional movements of large bodies of geese and ducks. It is very difficult, therefore, to ascertain the lines of flight, but we may conclude that many summer residents of California and northward bear well to the east in seeking their winter quarters in the tropics, as at least a dozen species which breed in California have not been observed much south of San Diego at any time, among these being such conspicuous species as Bullock's oriole and the Arkansas flycatcher, which, in common with the other species, occur far south on the mainland in Mexico in winter. Then there are summer residents of Washington, British Columbia and Alaska which have never been collected in California, though they spend the winter in the tropics. The high Sierra Nevada and Cascade ranges would seem to be an impassible barrier to the migrants, and they undoubtedly have great influence in determining lines of flight but not nearly as much as would naturally be supposed, as a number of species which winter in California migrate vertically and spend the summer on the east slope.