1. The young in the first nest were raised with no assistance from the male until the last two days, when he brought 11 meals in contrast to his mate’s total of more than 245. The young in the second nest were raised entirely by the female. 2. The first female incubated for periods ranging from 34 to 50 minutes, absenting herself for periods ranging from 9 to 26 minutes. The second female once incubated for 99 minutes at a stretch; her absences varied from 13 to 20 minutes. 3. Both females brooded for longer periods than the majority of arboreal Warblers that have been studied, averaging 15.1 and 18.3 minutes respectively. 4. Both females fed at slow rates, the average for the first being once in 19.7 minutes, for the second once in 16.3 minutes. * * * (6). Both females made definite efforts to get their last young out of the nest and to lead them to a distance.
Pitelka (1940b) gives many interesting details on the home life of the black-throated green warbler, illustrated with charts and tables that are not suitable for inclusion here, but his paper is well worth careful study.
Reading and Hayes (1933) made some intimate studies of these warblers at their nest; referring to the food of the young, they say: “Observations at less than two feet revealed the tremendous value of these birds as insect destroyers. Spiders, may-flies, green caterpillars (Anisota), ants, small noctuid moths, ichneumon flies, crane flies, and many smaller diptera made up the whole of their menu. While the few spiders and ichneumon flies were harmless or possibly beneficial, many of the other insects were injurious.”
Plumages.—Dr. Dwight (1900) calls the natal down sepia-brown and describes the juvenal plumage, in which the sexes are alike, as “above, sepia-brown or drab. Wings and tail dull black, edged with ashy or olive-gray; two wing bands white; the outer three rectrices largely white. Below, dull white, dusky on the throat, spotted on the breast and sides with dull olive-brown. Indistinct grayish white superciliary line. Dusky transocular streak.”
A partial postjuvenal molt, beginning in July and involving the contour plumage and the wing coverts but not the rest of the wings or the tail, produces the first winter plumage, in which the sexes are distinguishable. He describes the young male as—
above, greenish olive-yellow, the upper tail coverts ashy or plumbeous gray edged with olive yellow. The feathers of the crown and back especially have concealed black shaft streaks. The wing coverts are black, edged with olive green; two broad white wing bands tipped faintly with yellow. Below, faint primrose-yellow, white on the crissum; the breast and a spot on the flanks canary, the chin, sides of head and neck and superciliary line bright lemon-yellow; a variable area on the throat seldom including the chin, black, veiled by long narrow edgings, the sides and flanks broadly streaked and similarly veiled. Transocular and rictal streaks dusky; lores grayish. * * * In first winter plumage the female is browner than the male, without the black throat and the side streaks obscure; some specimens with much black may, however, easily be mistaken for dull first winter males.
The first nuptial plumage is acquired by a partial prenuptial molt, “which involves chiefly the head, chin and throat and not the rest of the plumage. The black chin is assumed by the male and the forehead becomes yellower by moult, wear removing the edgings everywhere so that the streakings below and the throat become jet-black. Young and old become practically indistinguishable, except that the wings and tail of the young bird will average browner and more worn with the edgings duller.” In the female, “the first nuptial plumage differs very little from the first winter, wear bringing out the streaking, while a few feathers are assumed by moult on the chin.”
A complete postnuptial molt occurs in July, producing the adult winter plumage, in which the male “differs somewhat from the first winter, the black of the throat extending uninterruptedly to the apex of the chin, further down on the throat, and in broader stripes on the sides; the wings and tail are blacker and the edgings grayer, especially on the tertiaries; the concealed black of the back more extensive. The veiling is conspicuous on the throat.” The adult winter female is much like the first winter male, “and may have considerable black on the throat, and even the chin.”
The adult nuptial plumage is acquired mainly by wear, with only slight indications of molt, as in the young bird. Dr. Dwight says of the female: “The adult nuptial plumage is, in extreme examples, hardly distinguishable from the male, but usually the black is much restricted and the chin yellow, merely spotted with black.”