Young.—We have no information on the incubation of the eggs, nor on the care and development of the young.
Plumages.—I have examined the nestlings sent to Brewster by C. A. Allen; they are about two-thirds fledged on the body and wings; the heads still show the long natal down, “hair brown” in color; the feathers of the back are “olive brown”; the wings are “clove brown,” with two narrow, white wing bars, faintly tinged with pale yellow; the breasts and sides are pale “hair brown” to “light grayish olive”; and the rest of the under parts are yellowish white. A young bird in fresh plumage, collected July 1, is probably in full juvenal plumage; its body plumage is similar to that of the nestlings, but there is some yellow on the forehead and throat, and the sides of the head and neck are decidedly yellow; however, this may be a bird that has assumed its first winter plumage at an unusually early date.
In first winter plumage, young birds of both sexes are much like the adult female at that season, mainly grayish olive-green above, with black streaks concealed or absent; forehead, sides of the head, and chin pale yellow; and the rest of the under parts buffy white, the sides browner. The broad, white tips of the lesser wing coverts have a black shaft streak or wedge, apparently characteristic of this plumage. There is probably a prenuptial molt involving much of the head and body plumage and the wing coverts, but the dull juvenal wings are retained until the next molt.
The complete postnuptial molt occurs in July and August. The fall plumages of both sexes are like the spring plumages, but the clear blacks and yellows are largely concealed by olive above and by buffy below.
Food.—The only item I can find on the food of the hermit warbler is the following short statement by Bowles (1906): “Their food consists of small spiders, caterpillars, tiny beetles, and flying insects which they dart out and capture in a manner worthy of that peer of flycatchers the Audubon warbler.”
Behavior.—The most marked trait of the hermit warbler is its fondness for the tree tops, spending much of its time in the tops of the tallest firs, often 200 feet or more above the ground, where it is very active and not easy to follow. But it builds its nest at lower levels, and often comes down to forage in the lower branches, in smaller trees and even in the underbrush, where it is not particularly shy and can be easily approached. It is a close sitter while incubating; Bowles had to lift one off its nest.
A hermit warbler watched by Miss Margaret W. Wythe, in Yosemite Valley, “was foraging in the upper parts of the trees and never came to the lower branches. Starting from near the trunk of a pine it would work out to the tip of one branch before going to another. Its demeanor while foraging was much more deliberate than that of any of the other warblers” (Grinnell and Storer, 1924).
Voice.—Rathbun (MS.) writes: “The song is quite strong, can be heard a considerable distance, and when given in full consists of five or six notes. The first note, rather faint, rises and then falls, with a slight accent at its close; if one is quite close to the singer, the note has a light lisping sound. This note is followed by another, similar but stronger and more prolonged. Then come three or four short, clear notes quickly given, the song ending with a prolonged rising one that closes sharply. Our interpretation of the song would be zweeo-zweeo-zwee-zwee-zwee-zweeck. Whenever an additional note is given, it is of the intermediate kind. One or two of these notes are, to us, suggestive of some heard in the song of Townsend’s warbler. The song is quite rapidly sung in an energetic way, being very distinctive and is pleasing. It resembles the song of no other warbler in the region.”
Bowles (1906) says that the song of the hermit warbler “consists of four distinct notes, as a rule, and is described as zeegle-zeegle, zeegle-zeek, uttered somewhat slowly at first but ending rather sharply.” Barlow (1899) states that “though not loud it would penetrate through the woods quite a distance and very much resembled tsit, tsit, tsit, tsit, chee chee chee, the first four syllables being uttered with a gradual and uniform speed, ending quickly with the chee chee chee.” Grinnell and Storer (1924) write:
The song of the male Hermit Warbler, while varying somewhat with different individuals, is sufficiently distinct from that of the other warblers of the region to make possible identification by voice alone. The song is most nearly like that of the Audubon Warbler but usually not so clear or mellow. A male bird observed at Chinquapin seemed to say seezle, seezle, seezle, seezle, zeek, zeek; just that number of syllables, over and over again. The quality was slightly droning, but not so much so as that of the Black-throated Gray Warbler. Another song, clearer in quality, heard in Yosemite Valley, was written ter´-ley, ter′-ley, ter´-ley, sic´, sic´, thus much more nearly like the song of the Audubon Warbler. Other transcriptions ranged between these two as to timbre. A rendering set down at Glacier Point June 16, 1915, was as follows: ser-weez´, ser-weez´, ser-weez´, ser´, ser´. The marked rhythm throughout, and the stressed terminal syllables, are distinctive features of the Hermit’s song. The call note is a moderate chip.