Throughout most of the eastern half of the United States the Blackburnian warbler is known only as a migrant, mainly from the Mississippi Valley eastward. Its summer range extends from Manitoba eastward to Nova Scotia, from Minnesota to New England, and southward in the Allegheny Mountains to South Carolina and Georgia, in the Lower Canadian and Upper Transition Zones. For its breeding haunts it prefers the deep evergreen woods where spruces, firs, and hemlocks predominate, or often swampy woods where the black spruces are thickly draped with Usnea, offering concealment for birds and nests.
In Massachusetts, which is about the southern limit of its breeding range in New England, William Brewster (1888) describes its haunts at Winchendon as follows: “On both high and low ground, wherever there were spruces in any numbers, whether by themselves or mixed with other trees, and also to some extent where the growth was entirely of hemlocks, the Blackburnian Warbler was one of the most abundant and characteristic summer birds, in places even outnumbering the Black-throated Green Warbler, although it shunned strictly the extensive tracts of white pines which D. virens seemed to find quite as congenial as any of the other evergreens.”
Gerald Thayer wrote to Dr. Chapman (1907) that at Monadnock, New Hampshire, it is “a very common summer resident. It is one of the four deep-wood Warblers of this region, the other three being the Black-throated Blue, the Northern Parula and the Canada. While all the other summer Warblers of Monadnock seem better pleased with various sorts of lighter timber, these four are commonest in the small remaining tracts of primeval woodland, and in the heaviest and oldest second growth. But despite this general community of habit, each of the four has marked minor idiosyncrasies. The Blackburnian favors very big trees, particularly hemlocks, and spends most of its life high above the ground.”
Professor Maurice Brooks (1936) says that Blackburnian warblers “are thoroughly at home in the deciduous second-growth timber that in so many places has replaced the coniferous forest. They range down to elevations of 2,500 feet in northern West Virginia. Here they associate with Golden-winged and Chestnut-sided warblers. A favorite perch is on some chestnut tree that has been killed by the blight.” Rev. J. J. Murray tells me that, in Virginia, it is “common above 1,500 feet, wherever there are conifers.” And Thomas D. Burleigh (1941) says of its status on Mount Mitchell in western North Carolina: “Although not known to breed above an altitude of approximately 5,000 feet, this species is fairly plentiful during the late summer in the fir and spruce woods at the top of the mountain, appearing regularly in July and lingering through September.”
Spring.—The Blackburnian warbler is apparently rare in spring in the Atlantic States south of North Carolina; its migration range extends westward to the plains of eastern Texas, eastern Kansas, and eastern Nebraska, but it is rare west of the forested regions of the Mississippi Valley. Professor Cooke (1904) says that the average rate of migration “from the mouth of the Mississippi to its source, where it breeds, appears to be scarcely 25 miles per day.” Forbush (1929) writes:
It is generally regarded as rare in migration in Massachusetts, though probably untold numbers pass over the state every year, but only a few stop here. It is not when the birds are migrating that we see them, but when they stop to rest. * * * I can recall but two instances in my lifetime when myriads of Blackburnian Warblers stopped here, though other similar flights probably have come when I was not there to see. At sunrise one morning in early May, many years ago, when the tiny green leaves were just breaking forth on the tall trees of the woods near Worcester, Blackburnians were everywhere in the tree-tops. They swarmed in the woods for miles. Years later, in Amesbury, on another May morning, the night flight, having met a cold wave from the north with a light frost, had come down to earth and the birds were busily looking for food; many Blackburnians and many other warblers were in the low shrubbery, in the grass, and even on plowed fields in every direction all through the village and about the farms. The sudden cold had stopped them. A few hours later as the day grew warmer they disappeared and were not seen again.
Brewster (1906) says: “We see the beautiful Blackburnian oftenest during the later part of May, in extensive tracts of upland woods, where it spends much of its time in the tops of the larger trees, showing a decided preference for hemlocks and white pines. In Cambridge I have repeatedly observed it in our garden and the immediate neighborhood, usually in tall elms or in blossoming apple trees.”
Nesting.—So far as I can learn, the nest of the Blackburnian warbler is almost always placed in a coniferous tree at heights ranging from 5 feet to over 80 feet above the ground; nests have been reported many times in hemlocks, which seems to be a favorite tree, but also in spruces, firs, tamaracks, pines and even a cedar. Ora W. Knight (1908) says: “I have found them breeding in colonies as a rule, that is to say, in a rather dense, mossy carpeted tract of evergreen woods near the pond at Pittsfield [Maine], covering perhaps a square mile, there were about ten pairs of these birds to be found, and in a tract of similar woods about half this size at Bangor there are often six or eight pair nesting. In other words, in suitable localities they tend to congregate in loosely scattered assemblies, while in less suitable spots, generally none, or at most a single pair will be found.” Of a nest found near Winchendon, Mass., Brewster (1888) writes:
The nest, which was found by watching the female, was built at a height of about thirty feet above the ground, on the horizontal branch of a black spruce, some six feet out from the main stem. Its bottom rested securely near the base of a short, stout twig. Above and on every side masses of dark spruce foliage, rendered still denser by a draping of Usnea (which covered the entire tree profusely), hid the nest so perfectly that not a vestige of it could be seen from any direction. This nest is composed outwardly of fine twigs, among which some of the surrounding Usnea is entangled and interwoven. The lining is of horse hair, fine, dry grasses, and a few of the black rootlets used by D. maculosa. The whole structure is light and airy in appearance, and resembles rather closely the nest of the Chipping Sparrow.
The highest nest of which I can find any record is one reported by Dr. C. Hart Merriam (1885), found by A. J. Dayan in a grove of large white pines (Pinus strobus), in Lewis County, N. Y. It was saddled on a horizontal limb of one of the pines, about 84 feet from the ground and about 10 feet out from the trunk. “The nest is large, substantial, and very compact. It consists almost entirely of a thick and densely woven mat of the soft down of the cattail (Typha latifolia), with seeds attached, and is lined with fine lichens, horse hair, and a piece of white thread. On the outside is an irregular covering of small twigs and rootlets, with here and there a stem of moss or a bit of lichen.”