The first nuptial plumage is acquired by a partial prenuptial molt in late winter, which involves a large part of the body plumage, but not the wings or the tail. “The black streaks of the chin and throat are acquired, veiled with white, and the loral, subocular and auricular regions become jet-black. The brown primary coverts distinguish young birds and the chin is less often solidly black than in adults.”
The adult winter plumage is acquired by a complete postnuptial molt, beginning early in July. It differs from the first winter dress "in having the chin and throat heavily streaked with irregular chains of black spots veiled with white edgings, the wings and tail blacker and the edgings a brighter gray. * * * The female has corresponding plumages and moults, the first prenuptial moult often very limited or suppressed. In juvenal dress the wings and tail are usually browner with duller edgings and the streaking below obscure. In first winter plumage the streakings are dull and obscure everywhere, a brown wash conspicuous on the flanks and sides of the throat. The first nuptial plumage is gained chiefly by wear through which the brown tints are largely lost, the general color becoming whiter and the streaks more distinct. The adult winter plumage is rather less brown than the female first winter, the streaking less obscure and the wings and tail darker. The adult nuptial plumage, acquired partly by moult, is indistinguishable with certainty from the first nuptial.”]
Food.—McAtee (1926) summarizes the food of the species thus:
In its excursions over the trunks and larger limbs of trees the Black and White Creeper is certainly not looking for vegetable food, and only a trace of such matter has been found in the stomachs examined. The food is chiefly insects but considerable numbers of spiders and daddy-long-legs also are eaten. Beetles, caterpillars, and ants are the larger classes of insect food, but moths, flies, bugs, and a few hymenoptera also are eaten. Among forest enemies that have been found in stomachs of this species are round-headed wood borers, leaf beetles, flea beetles, weevils, bark beetles, leaf hoppers, and jumping plant lice. The hackberry caterpillar, the hackberry psyllid, an oak leaf beetle Xanthonia 10-notata, and the willow flea beetle, are forms specifically identified. Observers have reported this warbler to feed also upon ordinary plant lice, and upon larvae of the gypsy moth.
Forbush (1929) adds the following observation: “The food of this bird consists mostly of the enemies of trees, such as plant-lice, scale-lice, caterpillars, both hairy and hairless, among them such destructive enemies of orchard, shade and forest trees as the canker-worm and the gipsy, brown-tail, tent and forest tent caterpillars. Wood-boring and bark-boring insects, click beetles, curculios and many other winged insects are taken. Sometimes when the quick-moving insects escape its sharp bill, it pursues them on the wing but most of its attention is devoted to those on the trees.”
H. H. Tuttle (1919), speaking of the male parent feeding the young birds, says: “The fare which he provided was composed entirely of small green caterpillars, cut up into half-lengths.”
Behavior.—The black-and-white warbler seems set apart from others of the group, perhaps because of its marked propensity for clambering over the trunks of trees and their larger branches. Although, like other warblers, it seems at home among the smaller twigs, it spends a large part of its time on upright surfaces over which it moves easily and quickly, upward, downward, and spirally, with great agility and sureness of footing, constantly changing direction, and not using the tail for support. As it scrambles over the bark, it switches from side to side as if at each hop it placed one foot and then the other in advance, and even on slim branches it hops in the same way, the tail alternately appearing first on one side of the branch and then on the other; it reminds us of a little schoolgirl swishing her skirt from side to side as she walks down the street. The bird is alert and watchful, and if it starts an insect from the bark, or sees one flying near, it may pursue it and catch it in the air.
H. H. Tuttle (1919) describes an extreme example of behavior simulating a wounded bird. He says: “She struck the leaves with a slight thud and turned over on her side, while the toes of one up-stretched leg clutched at the air and her tail spread slowly into a pointed fan. * * * Deceived for a moment then, I turned a step in her direction. She lay quite still except for a quivering wing. I reached out toward her with a small stick and touched her side; she screamed pitifully; I stretched out my hand to pick her up, but with a last effort she righted herself, and by kicking desperately with one leg, succeeded in pushing forward a few inches.”
We associate this warbler with dry, rocky hillsides where the ground is strewn with dead leaves, but the bird may breed also in the dry portions of shady, wooded swamps.
Voice.—The black-and-white is one of the high-voiced singers. Its song is made up of a series of squeaky couplets given with a back-and-forth rhythm, a seesawing effect, like the ovenbird’s song played on a fine, delicate instrument. It may be suggested by pronouncing the syllables we see rapidly four or five times in a whispered voice. In the distance the song has a sibilant quality; when heard near at hand a high, clear whistle may be detected in the notes. The final note in the song is the accented see.