As the breeding ranges of Hoover’s warbler and Audubon’s warbler approach each other in British Columbia and may even overlap it would not be strange if hybrids between these two closely related species should occasionally turn up. Joseph Mailliard (1937) calls attention to a number of such hybrids between both forms of coronata and auduboni. And more recently, Fred M. Packard writes to me: “I have inspected skins in most of the major museums in America to detect these hybrids, and have been surprised at the number I have found. All but two were taken in the Rockies or farther west, so that presumably the subspecies concerned is D. c. hooveri.”
PACIFIC AUDUBON’S WARBLER
Plate 34
HABITS
The Pacific Audubon’s warbler is a handsome western species closely related to our familiar myrtle warbler, which to a large extent it replaces, and is much like it in behavior and appearance; but it has one more touch of color in its brilliant yellow throat, five spots of yellow instead of four, and it has more white in the wings and tail. Although its breeding range does not extend nearly as far north as that of the myrtle warbler, it extends farther south, and to considerably higher altitudes, breeding largely in the Canadian Zone among the pines, firs, and spruces. Including the range of the Rocky Mountain form (memorabilis), which has not yet been admitted to the A. O. U. Check-List, the type race breeds from central British Columbia, central Alberta, and west-central Saskatchewan southward to southern California, northern Arizona, New Mexico, and western Texas. Throughout most of this range it is widely distributed in the lowlands only during the winter, retiring to the mountains for the breeding season.
In the mountains of New Mexico it has been found breeding at altitudes of from 7,500 feet to over 11,000 feet. In Colorado it breeds at similar elevations and perhaps up to nearly 12,000 feet. In southern California, Dr. Joseph Grinnell (1908) found it breeding in the San Bernardino Mountains from 9,000 feet “almost to timber limit, 10,500 feet elevation, at least. * * * This was one of the most abundant birds of the San Bernardino mountains, and was widely distributed from the lower edge of the Transition zone up through the Boreal.” Grinnell and Storer (1924) write:
The Audubon Warbler is the most widely distributed and the most abundant of all the species of wood warblers found in the Yosemite region. It occurs in numbers throughout the main forested districts of the mountains during the summer season, and it frequents the deciduous trees and brush of the foothill and valley country in the winter time.
Altitudinally its summer range extends from the beginning of the Transition Zone yellow pines on the west slope, at 3300 to 3500 feet, up through the lodgepole pines and other conifers of the Canadian and Hudsonian zones to the upper limit of unstunted trees at 10,000 feet or a little higher. * * *