This, the only form of _auduboni_ that breeds in the Huachucas, occurs during the summer months, though in rather limited numbers, in the higher pine regions from 8500 feet upwards. On one occasion, April 5, 1903, I secured a male _nigrifrons_ from a flock of _auduboni_ feeding in some live-oaks near the mouth of one of the canyons at an altitude of about 4500 feet, but this is the only time that I have seen it below the altitude given above; and it is also exceptional in the early date of its arrival. No more were seen until the second week in May, which seems nearer the usual time of arrival, for in 1902, the first was seen on May 9th. * * * Several specimens were taken intermediate in their characteristics between _auduboni_ and _nigrifrons_; some, of the size of the latter, though in color but little darker than _auduboni_, while some show every gradation of color between the two extremes. The black-fronted warbler averages somewhat larger than the Audubon's. _Nesting._--Before this warbler was known to be the breeding form in Arizona, O. W. Howard (1899) reported on two nests found in the Huachuca Mountains in 1898, and said that he had found "several nests" of Audubon's warblers in 1897 and 1898, all in these mountains. These were all, doubtless, nests of the black-fronted warbler. One of these was in a red fir tree about 15 feet up, and the other "was placed in the lower branches of a sugar-pine about fifty feet from the ground, and twelve feet out from the trunk of the tree. * * * The nests are very loosely constructed, being composed almost entirely of loose straws with a few feathers and hair for a lining." One of Howard's nests of this warbler, with four eggs, is in the Thayer collection in Cambridge. It was found in the same mountains, at an elevation of about 9,000 feet, saddled on the limb of a red spruce tree 35 feet above ground and well concealed in the foliage. It is rather a bulky nest made of shredded weed stems, fine strips of inner bark, fine rootlets and various other plant fibers, mixed with feathers of the Arizona jay, three long wing feathers of small birds and two small owl feathers; it is lined with fine fibers, horse and cattle hair, and jay feathers. Externally it measures about 3-1/2 inches in diameter and 2-1/2 in height; the inside diameter is about 2 inches and the cup is about 1-3/4 inches deep. James Rooney has sent me the data for a set of four eggs of the black-fronted warbler, taken by Clyde L. Field in the Santa Catalina Mountains in Arizona, June 2, 1938. The nest, placed 15 feet above ground at the end of a pine limb, was made of twigs and was lined with deer hair and a few feathers. A nest with four eggs, in the collection of Charles E. Doe, in Florida, was taken by the same collector in the same mountains on June 8, 1937; it was in a crotch of an aspen, 30 feet up.