The lowest nests that I have heard of are recorded in Frederic H. Kennard’s notes from Maine; one was only 51⁄2 feet up and the other 9 feet from the ground in small spruces. Mrs. Nice (1932) found a nest near her mother’s home in Pelham, Mass., that was “18 feet from the ground near the top of a cedar among comparatively open, young growth, 40 yards south of the house and 150 yards to the east of the great pines and hemlocks where the male habitually sang.” The only nest of this warbler that I have ever seen was found by watching the female building it, on June 16, 1913, on an island in Lake Winnipegosis, Manitoba; it was only about 10 feet from the ground, near the end of a drooping branch of a large black spruce that stood on the edge of some coniferous woods next to an open swale. The nest, shaded from above, was partly concealed from below by dense foliage and was, apparently, well made of soft fibers, deeply cupped, and lined with some dark material and a little willow cotton. I was not able to visit the island again.
In New York State and in Pennsylvania, the nests of the Blackburnian warbler are almost invariably placed in hemlocks. All of the four nests recorded by T. E. McMullen (MS.) from the Pocono Mountains, Pa., were in hemlocks. And Todd (1940) states that with one exception all the nests found by R. B. Simpson, of Warren, Pa., were in hemlocks, “at elevations varying from twenty to fifty feet. The exceptional nest was in a large chestnut, sixty feet from the ground.”
Dr. Roberts (1936) mentions a Minnesota nest “situated in an arbor vitae tree, directly over the entrance to a cabin,” and one “placed in a small spruce, close to the trunk, about 2 feet from the top of the tree and about 20 feet from the ground.” Another was found in “a jack-pine tree, 20 feet from the ground, 6 feet from the trunk, resting in a tangle of small branches, and concealed by a closely overhanging branch.”
Eggs.—The Blackburnian warbler lays normally 4 or 5 eggs, usually 4; in a series of 14 sets there are only 3 sets of 5. They are ovate to short ovate and slightly glossy. The ground color is snowy white or very pale greenish white, and is handsomely spotted and blotched with “auburn,” “bay,” “argus brown,” “Mars brown,” or “mummy brown,” with undertones of “brownish drab,” or “light vinaceous-drab.” On some eggs the drab marks are the most prevalent, with fewer but more prominent spots or blotches of dark brown shades, such as “Mars brown” and “mummy brown.” Others have spots of “auburn” and “bay” so concentrated that they form a solid band around the large end. In addition a few small scrawls of brownish black are often found. Generally speaking the markings tend to form a wreath, but some eggs are spotted more or less evenly all over the surface. The measurements of 50 eggs average 17.2 by 12.8 millimeters; the eggs showing the four extremes measure 18.0 by 13.6, 17.0 by 13.7, 15.6 by 12.5, and 17.1 by 12.0 millimeters (Harris).
Young.—We have no information on incubation and very little on the care of the young. The male has been seen to go onto the nest, and evidently shares occasionally in the duty of incubation. Both parents help in feeding the young, as noted by Mrs. Nice (1932) at the nest she was watching. When Mrs. Nice’s daughter climbed a tree near the nest, the female “assumed a peculiar attitude, her tail outspread and dropped at right angles to her body, her wings flipping rapidly and occasionally held stiffly up or down. The excitement caused the young to jump out on the ground where they could not be found.”
Plumages.—Dr. Dwight (1900) calls the natal down sepia-brown, and in speaking of the males, describes the juvenal plumage as "above, dark sepia-brown obscurely streaked on the back with clove-brown. Wings and tail clove-brown edged with olive-buff, the tertiaries and coverts with white forming two wing bands at tips of greater and median coverts; the outer three rectrices largely white. Below, white, washed with wood brown or buff on breast and sides, spotted, except on chin, abdomen and crissum, with dull sepia. Superciliary stripe cream-buff, spot on upper and under eyelid white; lores and auriculars dusky.”
A partial postjuvenal molt begins early in August, involving the contour plumage and the wing coverts but not the rest of the wings or the tail. This produces the first winter plumage, which he describes as “above, deep yellowish olive-gray, flecked on the crown and streaked on the back with black; obscure median crown stripe straw-yellow; rump and upper tail coverts black, edged with olive-gray. Wing coverts clove-brown edged with olive-gray and tipped with white forming two broad wing bands. Below, straw-yellow brightening to orange-tinged lemon on the throat, fading to buffy white on the crissum and narrowly streaked on the sides with black veiled by yellow edgings. Superciliary stripe and post-auricular region lemon-yellow orange-tinged. Auriculars, rictal streak and transocular stripe olive-gray mixed with black. Suborbital spot yellowish white.”
He says that the first nuptial plumage is “acquired by a partial prenuptial moult which involves most of the body plumage (except posteriorly), the wing coverts and sometimes the tertiaries but not the rest of the wings nor the tail. The full orange and black plumage is assumed, young and old becoming practically indistinguishable, the orange throat equally intense in both, the wings and tail usually browner in the young bird and the primary coverts a key to age.”
The adult winter plumage is acquired by a complete postnuptial molt in July, and “differs little from the first winter dress, but the yellow more distinctly orange, the transocular and rictal streaks, the crown and auriculars distinctly black, veiled with orange tips, the streaking below heavier and broader, the wings and tail blacker and the edgings grayer.” The adult nuptial plumage is acquired as in the young bird; this molt evidently begins in February, while the birds are in their winter quarters, and is usually finished before they reach their summer homes.
Of the females, Dr. Dwight says: