Specimens examined from the northern regions (Great Slave Lake, Mackenzie River, and Yukon) to Guatemala; from Atlantic States to East Humboldt Mountains, Nevada, and from intervening localities. The extremes of variation are the brownish-olive of eastern and the clear dark greenish-olive of remote western specimens. There is no observable difference between a Guatemalan skin and one from Fort Bridger, Utah.
Habits. The Olive-backed Thrush, or “Swamp Robin,” has very nearly the same habitat during the breeding season as that of the kindred species with which it was so long confounded. Although Wilson seems to have found the nest and eggs among the high lands of Northern Georgia, it is yet a somewhat more northern species. It does not breed so far south as Massachusetts, or if so, the cases must be exceptional and very rare, nor even in Western Maine, where the “Ground Swamp Robin” (T. pallasi) is quite abundant. It only becomes common in the neighborhood of Calais.
It is, however, most widely distributed over nearly the entire continent, breeding from latitude 44° to high Arctic regions. It winters in Guatemala and southward as far as Ecuador and Brazil.
In its habits this thrush is noticeably different from the T. pallasi, being much more arboreal, frequenting thick woods; rarely seen, except during its migrations, in open ground, and seeking its food more among the branches of the trees.
Mr. Ridgway found this species very abundant among the Wahsatch Mountains, where it was one of the most characteristic summer birds of that region. It was breeding plentifully in the cañons, where its song could be heard almost continually. It inhabited an intermediate position between T. auduboni and T. fuscescens, delighting most in the shrubbery along the streams of the cañons and passes, leaving to the T. auduboni the secluded ravines of the pine regions higher up, and to the T. fuscescens the willow thickets of the river valleys. He did not meet with it farther west than the East Humboldt Mountains. The song, in his opinion, resembles that of the Wood Thrush (T. mustelinus) in modulations; but the notes want the power, while they possess a finer and more silvery tone.
The song of this species has a certain resemblance to that of T. pallasi, being yet quite distinct, and the differences readily recognized by a familiar ear. It is more prolonged; the notes are more equal and rise with more regularity and more gradually, are richer, and each note is more complete in itself. Its song of lamentation when robbed of its young is full of indescribable pathos and beauty, haunting one who has once heard it long after.
When driven from the nest, the female always flies to a short distance and conceals herself; making no complaints, and offering no resistance.
These birds, in a single instance, have been known to reach Eastern Massachusetts early in April, in an unusually early season, but they generally pass north a few weeks later. They make no prolonged stay, and are with us rarely more than three or four days. Their return in the fall appears to be, at times, by a more inland route. They are then not so numerous near the coast, but occasionally are abundant.
Their nests in Nova Scotia, wherever observed, were among the thick woods, on horizontal branches of a forest-tree, usually about five feet from the ground. Those observed in the Arctic regions by Mr. Kennicott were frequently not more than two feet from the ground.
The nests average about four inches in diameter and two in height, the cavity being three inches wide by about one and a half deep. They are more elaborately and neatly constructed than those of any other of our thrushes, except perhaps of T. ustulatus. conspicuous among the materials are the Hypnum mosses, which by their dark fibrous masses give a very distinctive character to these nests, and distinguish them from all except those of the T. ustulatus, which they resemble. Besides these materials are found fine sedges, leaves, stems of equisetaceous plants, red glossy vegetable