“The first song has notes on three different pitches. The first notes, three to nine but commonly four or five, are all on the same pitch, usually the highest; the next note, usually a major third lower, is the lowest; the next, and last, is between them. Such a song might be written sree sree sree sree sree tro tray, all the notes being of equal length. I have 34 records of this song, 23 of which follow this form. A few are arranged with the last note highest, or lowest, or on the same pitch as the first. The first notes are sometimes varied by alternating short and long notes or sometimes are united in a long trill.
“The second song consists of four or five notes only, with a definite time arrangement—3 2 1 1 or 3 2 1 1 1; that is, the first note is three times as long as the last and the second note twice as long. The third and fourth notes are on the same pitch, but the others are on different pitches, so that the song might be written treee tray to to, or a 5-note song treee tray tray to-to tay. The notes, as in the first song, are on three different pitches, but they vary in every possible way as to which note is highest and which lowest, so that there are six possible arrangements of these different pitches in a 4-note song where the last two notes are always on the same pitch. In my collection of 52 records of this song I have samples of all six, and of these 33 are of four notes, while only 19 have the fifth note added.
“Songs of this species vary from 11⁄5 to 2 seconds in length, the first song from 12⁄5 to 2 seconds, and the second 11⁄5 to 14⁄5 seconds. The pitch varies from F‴to E‴´, a half tone less than an octave. One peculiar song of the first type, however, was prefixed by a wren-like chatter that was pitched on B″, but the remaining song was normal in pitch. Single songs average about one and a half tones in range, but the majority of the songs of the first type range two tones, and those of the second type two and a half tones.
“The song is to be heard from the first arrival of the species in migration until shortly after the first of August. In 14 seasons the average date of late song in Allegany State Park is August 2, the earliest is July 25, 1927, and the latest August 11, 1935 and 1937. While there is no regular revival of full song after the molt, there is occasional singing of a primitive character.”
C. Russell Mason tells me of a song in which the high, musical note was given six times instead of the usual once. Francis H. Allen has heard some variations in the songs and has sent me these notes: “One bird added at the end of the familiar zee zee zee zoo zee a coda of an intricate and wrenlike quality, and sang this beautiful song constantly. Another introduced a trill after the second note of the ‘trees, trees’ song and ended it with a low note. Another bird sang a variant of the ‘trees, trees’ song, in which it substituted for the final high note a lower-pitched su-eet su-eet without the familiar z quality.” He and Dr. W. M. Tyler heard one that “sang in addition to one of the characteristic songs of the species an entirely unrecognizable one that went something like ti-ti-ti-ti-ti-zp. The first five notes were very thin and slight with a very short pause before the last one, and the final note was a short emphatic buzz. Once this song ran into a characteristic song without a pause between.” He refers to the ordinary call-note as a distinctive chet, suggesting that of the myrtle warbler, but thinner. “On the occasion in early June, I heard from a male bird a succession of chippering notes which I had formerly attributed to the young alone. He alternated these notes with singing.”
Many other somewhat similar renderings have appeared in print, both in syllables and in human words, most of which seem to recall the song to mind. Some of the best of the wordings are trees, trees, murmuring trees and sleep, sleep, pretty one, sleep (Torrey, 1885); good Saint Theresa (Maynard, 1896); and take it, take it, leisurely (Stanwood, 1910b). Miss Stanwood pays this tribute to the charm of the song: “His voice is suggestive of the drowsy summer days, the languor of the breeze dreamily swaying the pines, spruces, firs, and hemlocks. It recalls the incense of evergreens, the fragrance of the wild strawberry, the delicate perfume of the linnea. No other bird voice is so potent to evoke that particular spell of the northern woods.”
The black-throated green warbler is a most persistent singer. The Nices (1932) say that the first warbler "gave 466 songs in a single hour and more than 14,000 in the 94 hours of observation.” According to Albert R. Brand (1938), the approximate mean number of vibrations per second in the song is 6,025, in the highest note 6,750 and in the lowest note 5,125. This compares with a mean of 8,900 for the black-polled warbler, which is the shrillest passerine bird song.
Field marks.—The conspicuous, bright yellow cheeks, the olive-green back, the prominent black throat, the two white wing bands, and the white outer webs of the lateral tail feathers will distinguish the male in breeding plumage. The female is duller and has less black, or none at all, on the throat. Young birds in the fall are much like the female. See the descriptions under Plumages.
Fall.—The fall migration of the black-throated green warbler begins during the latter part of August, continuing through September and often through much of October. It seems to be a reversal of the route followed in the spring. Similar haunts are frequented in the fall in the company of vast congregations of other species. A remarkable flight of various species of warblers was seen by Rev. W. F. Henninger in Scioto County, Ohio, an account of which is quoted by W. L. Dawson (1903) as follows:
On September 28, 1899, I ran into a company of warblers which I would place conservatively at two thousand individuals. It was like a regular army as it moved up a long sloping hillside, and with wonderful rapidity. The wind was blowing almost a gale from the north, and the birds allowed themselves to be urged before it in the direction of their ultimate retreat, like half-stubborn autumn leaves. Lisping, chipping, whirling, driving, they hurried on and I after at full speed, panting, and wishing devoutly for a better chance to identify the fleeing forms. Arrived at the top of the hill the army suddenly halted and when I arrived breathless I had time to note the arrangement by species, not rigid indeed, but sufficiently striking to command attention. In the center were seen Hooded Warblers and a sprinkling of Chestnut-sides. On either side of these in turn were Black-throated Greens and Sycamores, about two hundred of each; while the wings proper were held by Bay-breasts and Black-polls in enormous numbers. * * * As the birds deployed to feed the specific lines were not quite obliterated.