Like the hermit warbler, a bird of the higher altitudes in the mountains of California, the Calaveras warbler, on reaching the cooler climate of the northwest, is to be found as a rule only on the driest prairies. Here the birds frequent the scattered clumps of young oaks and fir trees that have reached a height of some three or four feet, and which border the large tracts of dense fir timber. It is a noteworthy fact that, while these birds are not often to be found more than a hundred yards outside of the forests, they are seldom or never seen inside of the dividing line where the heavy timber meets the prairie. Also they do not encroach upon the hillside territory of the lutescent warbler, which bird in turn does not appear on the prairies but confines itself to the brush-covered uplands. _Nesting._--Dr. Osgood (1896) found three nests of the western Nashville, or Calaveras, warbler near Fyffe in the Sierras; two of these were concealed under dead leaves, one of which was partially concealed by a little sprig of cedar at the foot of a cedar stump, and the other was under a little tuft of "mountain misery"; the third was in a thick patch of "mountain misery" and was "well embedded among the roots of this little shrub, and shaded by its thick leaves." In the Yosemite Valley, Grinnell and Storer (1924) found a nest in what must be an unusual situation: The location was only about 75 feet from the much traveled south road on the Valley floor and at the base of the talus pile of huge boulders. The nest was in the face of one of the larger of these boulders, partly in a diagonal fissure. It was on the north side of the rock and so never received any direct rays of sunlight. The whole face of the boulder was covered densely with yellow-green moss which in places was overlaid by olive-gray lichens. The nest was 43 inches from the base of the rock and about 60 inches from the top. Another nest was found in a hollow of the ground at the base of an azalea bush, near an old road along the hillside. The creek itself was about 50 feet distant. This nest was 3 inches across the outside and about 2 inches high, the cavity being 1-1/4 inches deep. Strips of bark of the incense cedar, plant fibers, and horsehair comprised the building material. The Bowles brothers (1906) say that the nests are very much like those of the eastern Nashville warbler, as taken by them in Massachusetts. In Washington, "the site chosen is usually at the base of a very young oak, or fir, tho on one occasion we found one built under some blackberry vines at the base of a large fir stub. The nests are sunk well into the ground or moss, and are so well concealed as to defy discovery unless one flushes the bird."