Voice.—Aretas A. Saunders has contributed the following study of the song of this warbler:
The song of the worm-eating warbler is a simple trill, varying from 12⁄5 to 21⁄5 seconds in length. It is usually all on the same pitch, but a few songs rise or fall a half tone, and one record I have rises a full tone and then drops a half tone at the end. The quality is not musical, but rather closely resembles some forms of the chipping sparrow’s song. The pitch varies from G sharp‴ to F sharp‴′, one tone less than an octave.
The majority of songs are a continuous trill, that is, the notes are too fast to be separated and counted by ear. I have three examples that are broken into short, very rapid notes. Two of these were of 18 notes and one was of 28. Most of the songs vary in loudness, becoming loudest in the middle, or beginning loud and fading away toward the end. One record becomes louder toward the end and ends abruptly.
Francis H. Allen describes in his notes a song “remarkably like that of the chipping sparrow, but more rapid than is usual with that species, I think, and perhaps shorter, though not so short as the chippy’s early-morning song. The bill quivers with the song, but does not close between the chips. The bird sang constantly as it flitted about, usually 10 or 20 feet from the ground, seeming to prefer dead branches and twigs.”
Almost everyone emphasizes the resemblance of the song to that of the chipping sparrow. Burns (1905) says: “I can distinguish no difference between the notes of this species and the Chipping Sparrow; the first may be a trifle weaker perhaps.” But, in some notes recently sent to me, he writes: “The song has often been described as easily mistaken for that of either the chipping sparrow or slate-colored junco, but by no means by an expert. The notes of the worm-eater have a buzzing or bubbling quality not easily described, but are quite distinct from the flat notes of the species named above.” And Eugene P. Bicknell (1884) writes: “The songs of no other three birds known to me are more alike than those of the Worm-eating Warbler, the Chipping Sparrow, and the Slate-colored Snowbird.” He is in agreement with Saunders and Burns that this bird sings from the time of its arrival until the last of June or early July, but he also says: “On July 10, 1881, several of these birds were silently inhabiting a small tract of woodland, their first season of song having passed; here, on August 14, and again on the 21st, they were found in fine plumage and in full song.” Evidently there is a cessation of singing during the molting period.
Burns (1905) says of the song: “The series of notes may be uttered while perched, or creeping about the lower branches of the trees, sapling tops, bushes or fallen brush, or while on the ground. With slightly drooping tail and wings, puffing out of body plumage, throwing its head back until the beak is perpendicular, it trills with swelling throat an unvarying Che-e-e-e-e-e-e, which does not sound half so monotonous in the woods as does the Chippy’s lay in the open.”
Dr. Chapman (1907) adds: “Mr. W. DeW. Miller of Plainfield, New Jersey, tells me that he has on two occasions heard a flight song from this species. It is described by him as much more varied and musical than the ordinary song, though lacking in strength. It was given as the bird flew through the woods at an even level, not rising above the tree-tops, as does the Oven-bird and other flight singers.”
Field marks.—When seen walking around on the ground the worm-eating warbler might be mistaken for an ovenbird, but the conspicuous black stripes on the head of the former are quite distinctive, very different from the head markings of the latter. Moreover, the ovenbird is distinctly spotted on the breast, whereas the warbler has a plain, unmarked breast and no conspicuous wing bars. Except for the bold stripes on the head it is just a plain olive and buffy warbler in all plumages.
Enemies.—Says Burns (1905): “This Warbler’s enemies are wood-mice, red squirrels and hunting dogs; the latter will sometimes push up and overturn the nest; an occasional weasel or blacksnake may destroy a few young. The percentage of loss while in the nest cannot be high.”