DENDROICA AUDUBONI NIGRIFRONS (Brewster)
BLACK-FRONTED AUDUBON’S WARBLER
HABITS
The black-fronted Audubon’s warbler was originally described by William Brewster (1889) as a distinct species, based on a series of five specimens collected by M. A. Frazar in the Sierra Madre Mountains of Chihuahua, Mexico, in June and July, 1888. He gave as its characters: “Male similar to D. auduboni but with the forehead and sides of the crown and head nearly uniform black, the interscapulars so closely spotted that the black of their centres exceeds in extent the bluish ashy on their edges and tips, the black of the breast patch wholly unmixed with lighter color. Female with the general coloring, especially on the head, darker than in female auduboni; the dark markings of the breast and back coarser and more numerous; the entire pileum, including the yellow crown patch, spotted finely but thickly with slaty black.” He admits that it is closely related to D. auduboni, “so closely in fact that the two may prove to intergrade,” but he found no indications of such intergradation. Later, however, Leverett M. Loomis (1901) called attention to the fact that several birds, collected in the Huachuca and Chiricahua Mountains, in Arizona, showed signs of intergradation with breeding birds from central California. These were taken by W. W. Price, establishing this bird as an addition to our fauna, and resulting in its reduction to subspecific rank. It is known to breed in the Huachuca Mountains and in the high Sierras of northwestern Mexico, ranging south to Guatemala. Swarth (1904) says of the status of the black-fronted warbler in Arizona:
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 31⁄2 inches in diameter and 21⁄2 in height; the inside diameter is about 2 inches and the cup is about 13⁄4 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.
Eggs.—The measurements of 16 eggs average 18.5 by 13.6 millimeters; the eggs showing the four extremes measure 19.8 by 14.0, 19.5 by 14.4, 17.3 by 13.9, and 17.6 by 12.4 millimeters (Harris).