Hab. Entire North America, and in winter into South America as far as Ecuador, Cayenne, and Trinidad. Not recorded from West Indies, where replaced by allied species.
In the great abundance of this species and its wide range of distribution, there are many variations in size and color, though none that are not readily understood. In young birds the yellow of the tail-feathers is more restricted, sometimes confined to the edge of the inner webs. In adults there is occasionally a tinge of orange in the forehead.
Sylvia rathbonia of Audubon is described with even tail, and the tail-feathers brown, edged externally with yellow; the reverse of æstiva. It is generally, however, considered a synonyme.
Birds of this type (“Golden Warblers”) of six or eight additional species are known to occur in the West Indies, the Galapagos, and in Middle America; one of them, D. bryanti, possibly to be met with in Southern Arizona. (See Baird, Review Am. Birds, 193.)
After comparing a series of about one hundred and twenty North and Central American specimens (the latter being winter visitors to the region where obtained), nothing really characteristic of any particular region can be detected. Specimens from the Pacific coast of the United States are perfectly identical in colors with those from the Atlantic States; and they agree in size and proportions, except of the bill, which is appreciably longer and broader in the Eastern than in the Western birds. The most highly colored examples are from the interior regions, along the Mississippi Valley from Louisiana to Northern Illinois, and over the plains north to Fort Simpson. The majority of the specimens from this region are just appreciably different from others, in having the yellow more intense and prevalent, almost subduing the olive shades above; the crown more tinged with orange. Sometimes (as in No. 4,301, Calcasieu Pass, La.) the rump and upper tail-coverts are absolutely pure yellow, only a medial stripe on the feathers being olivaceous like the back. The orange-rufous tinge on the crown is deepest in Nos. 4,665, Fort Lookout, and 4,300, Calcasieu Pass.
Three adult summer males from Alaska (Nos. 54,429, Kodiak; 54,425, Yukon River; and 27,267, Fort Yukon), as well as one from Maine (52,378, Calais), differ from others in having the olive pervading the whole surface above, even to the bill, the forehead being only tinged with yellow, and the edges of wing-coverts merely inclining to this color. The lower parts are much as in Southern specimens, though the yellow is less intense.
Females from Arizona (as 49,712, Camp Grant, May; 40,664, Fort Whipple, May; and 34,340, Los Pinos, New Mexico, June) differ from others in very bleached plumage, the lower parts being almost white, and the upper
surface quite ashy. But this is, in fact, an actual bleaching, frequently to be seen in birds from that region.
Habits. The geographical range of the common Summer Yellow-Bird is very nearly coextensive with North America. In its northern distribution it is found as far toward the arctic shores as any of our land birds. Richardson speaks of it as well known throughout the fur countries as far as the woods extend, and mentions meeting with it among the earliest arrivals in spring, coming in company with the equally well-known Robin and the Grakle. At Fort Franklin, latitude 66°, he saw it the 15th of May, about the time of its first appearance in New England. This was supposed to be the limit of its northern range, but more recent observations give abundant evidence of its presence, in considerable numbers, to the very shores of the Arctic Ocean. The late Mr. Hepburn, in manuscript notes, states it to be a common summer visitant both of California and Vancouver’s Island, and that along the coast he has traced it as far north as the frontier line of 54° 40′, where it arrives at the beginning of May, but does not nest until the end of the month.
Mr. Dall, in his notes on the birds of Alaska, states that this Warbler is a rather common bird all through that territory, and gives its arrival as about the 10th of May.