Young birds and females have duller colors than the adult males and are browner in the fall than in the spring. Adults doubtless have a complete postnuptial molt in late summer.
Behavior.—Grace’s warbler is a bird of the pines, spending most of its time in the towering tops of the tallest trees. It is sometimes seen in other conifers such as hemlocks and spruces, but very seldom on or even near the ground. Dr. Wetmore (1920) says: “Usually they were found in the tops of the Yellow Pines where they worked about rather leisurely, exploring the smaller limbs and at short intervals pausing to sing. * * * Occasionally one was found working about through the oak undergrowth at times coming down almost to the ground. The flight was undulating and rather quick and jerky.”
Dr. Coues (1878) writes: “They are seen coursing among the branchlets, skipping at apparent random through the endless intricacies of the foliage, hovering momentarily about the terminal bunches of needles, and then dashing far out into clear space, to capture the passing insect with a dexterous twist and turn. So the season passes, till the young are on wing, when the different families, still with bonds unbroken, ramble at leisure through the woods, the young birds timid and feeble at first, venturing shorter flights than their parents, who seem absorbed in solicitude for their welfare, and attend them most sedulously, till they are quite able to shift for themselves.”
We found Grace’s warbler to be an active, restless species. We could often locate one by its song coming from lofty top of some tall pine, but before we could see its diminutive form, we would hear its song coming from some distant tree farther up the mountain side; and so we would follow the little songster from tree to tree, seldom getting more than a fleeting glimpse of it. At times, however, when it was more interested in feeding than in singing, we could see it quietly gleaning its insect food along the smaller branches and twigs after the manner of the pine warbler. We never saw it on or near the ground.
Voice.—Dr. Wetmore (1920) says that the song of Grace’s warbler, as heard by him at Lake Burford, N. Mex., “was a rapid repetition of notes somewhat reminiscent of the efforts of the Chipping Sparrow, but with the notes evenly spaced, not blurred at the end, and closing abruptly, so that the last syllable was as strongly accented as any of the others. It resembled the syllables chip chip chip chip chip given in a loud tone.”
Dr. Walter P. Taylor has sent me some notes on the song, which he calls “rather a modest utterance conspicuously lacking in strength. Song, tseet tseet tseet tseet zeekle zeet. A better rendering is tsew tsew tsew tsew tsew tsee tsee tsee tsee tseeeip! The song has something of a yellow warbler quality. I find it extremely hard to put down on paper anything that remotely resembles it.” Again he writes it “tchew tchew tchew, more slowly uttered, followed by tsip tsip tsip tsip tsip, rapidly repeated.”
Field marks.—Grace’s is one of the smallest of our wood warblers, a tiny bird. It shows a striking resemblance to the yellow-throated warbler, but it is much smaller, has no black in the cheeks, and it has a yellow rather than a white mark below the eye. The adult male in spring is light bluish gray above, marked on the head and back with black spots, with a bright yellow throat, two white wing bars, and much white in the tail. Females, young birds, and males in the fall are similar but browner.
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