Worm-eating Warbler

Published by the Smithsonian Institution between the 1920s and the 1950s, the Bent life history series of monographs provide an often colorful description of the birds of North America. Arthur Cleveland Bent was the lead author for the series. The Bent series is a great resource and often includes quotes from early American Ornithologists, including Audubon, Townsend, Wilson, Sutton and many others.

Bent Life History for the Worm-eating Warbler – the common name and sub-species reflect the nomenclature in use at the time the description was written.

The breeding range of the worm-eating warbler covers much of the central portion of the United States east of the prairie regions. Its center of abundance seems to be in the vicinity of Pennsylvania, but it breeds less abundantly northward to southern Iowa, New York, and New England and southward to Missouri and to northern Alabama and Georgia, as well as in much of the intervening wooded region, where it is essentially a woodland bird.

The distribution, migration, and habits of this warbler were but poorly understood by the early writers on American birds, and neither Wilson nor Audubon ever saw its nest; the latter’s description of the nest, probably from hearsay, is entirely wrong. Frank L. Burns writes to me: “Bartram neglected to list this species, although he had furnished the type to Edwards 35 years earlier, and from the information furnished by the youthful Bartram it doubtless received its name, which is a misnomer perpetuated by Gmelin in his Motacilla vermivora.” Mr. Burns says further on in his notes: “I searched for 10 seasons before I found my first nest, and oddly enough it was through the parent bird carrying a ‘worm’ to its young; nevertheless I have since thought that a more fitting name for the species would have been hillside or laurel warbler.”

Hillside warbler would not be a bad name for this bird, which shows a decided preference for wooded hillsides covered with medium-sized deciduous trees and an undergrowth of saplings and small shrubbery. Often a running stream with numerous swampy places, overgrown with brier tangles and alders, bounds the base of the hill as an additional attraction. It is seldom seen outside of its favorite woods and returns year after year to the same chosen haunts.

W. E. Clyde Todd (1940) says that in western Pennsylvania “wooded slopes are its chosen abodes, the shadier and cooler the better. * * * Deep ravines, down which trickle little streams, and the slopes of which support good stands of deciduous trees, with plenty of shrubbery and bushes for cover, are favorite resorts.” In Ritchie County, W. Va., William Brewster (1875) found it “most partial to the retired thickets in the woods along water courses, and seldom or never found in the high open groves.~~ Spring: The northward movement of the worm-eating warbler evidently begins in March, as the earliest arrivals from the Bahamas, the West Indies, and Cuba reach southern Florida during the first week in April. From its main winter resorts in Central America the flight seems to be partially across the Gulf of Mexico. Professor Cooke (1904) says in part: “The time of arrival on the coasts of Louisiana and Texas is about the same as in southern Florida. * * * Houston is the southernmost point in Texas from which it has been recorded to date, and Alta Mira is the northernmost point of record in Mexico. Since the species is apparently not common west of Louisana or north of Vera Cruz, it is probable that the principal line of migration is from Yucatan and the coast immediately west of Yucatan directly north to the northern coast of the Gulf of Mexico.” According to Williams (1945) the species is common on the coast of Texas in spring, and it probably migrates along the coast. Thence the migration proceeds northward through the Mississippi Valley and through the Atlantic Coast States east of the Alleghenies, the warblers reaching the more northern breeding grounds by the middle of May, where nesting activities begin as soon as mates have been selected.

Nesting: Evidently Thomas H. Jackson, of West Chester, Pa., was the first to report the discovery of the nest of the worm-eating warbler; he published an account of it in the American Naturalist for December 1869, from which Baird, Brewer, and Ridgway (1874) quote as follows: “On the 6th of June, 1869, I found a nest of this species contaming five eggs. It was placed in a hollow on the ground, much like the nests of the Oven-Bird (Seiuru8 auracapillus), and was well hidden from sight by the dry leaves that lay thickly around. The nest was composed externally of dead leaves, mostly those of the beech, while the interior was prettily lined with the fine, thread-like stalks of the hair-moss (Polytrichium). * * * So close did the female sit that I captured her without difficulty by placing my hat over the nest.”

This nest was quite characteristic of the species. Mr. Burns writes to me: “The nest, well hidden under a drift of dead forest leaves, never varied in composition in over a hundred examples examined by me, in partly skeletonized leaves and the characteristic reddish-brown lining of the flower stem of the hair moss.” Every one of 50 nests found by Mr. Jackson was lined with these flower stems, and out of 34 nests reported by Dr. Samuel S. Dickey (1934) only one failed to contain this material, being lined with “black and gray horsehair.” Samuel B. Ladd (1887) says that “sometimes fine grass and horse-hair are used as part of the lining.” Dr. Chapman (1907) writes: “Nests taken by J. N. Clark at Saybrook, Connecticut (C. W. C.) are composed of decayed leaves and lined with stems of maple seeds.” And there are probably a few other exceptions to the rule.

Most observers agree that the worm-eating warbler prefers to nest on hillsides, either sloping or steel), but a number of nests have been found on the sides of deep, shady ravines, or on steep banks. Mr. Ladd (1887), however, states: “I have observed that these birds are not confined necessarily to hill-sides, as was heretofore supposed, as I have taken three sets on level ground and in rather open places, with little shade. The experience of Mr. Thomas 11. Jackson of this place, who has taken ten nests this year, corroborates this fact.”

The nests are generally well concealed under a canopy of dead leaves, drifted by the wind and lodged against a maple, beech, dogwood, or ash sapling, or under hydrangea, laurel, or rhododendron bushes, or under some bunch of weeds or other obstruction. They are sometimes concealed under the roots of a tree or in a cavity in a bank where they are protected somewhat by fallen leaves.

Eggs: The number of eggs laid by the worm-eating warbler varies from 3 to 6, but the set usually consists of 4 or 5. The eggs are ovate or short ovate, sometimes rather pointed, and only slightly glossy. The white ground color is speckled and spotted with shades of “russet,” “vinaceous russet,” and “auburn,” intermingled with “light brownish drab” and “light vinaceous-drab.” The markings, usually more thickly grouped at the large end, vary considerably, some eggs being boldly marked, while others are almost immaculate, or have just a few pale freckles of “light brownish drab” and “fawn.” The measurements of 50 eggs average 17.4 by 13.6 millimeters; the eggs showing the four extremes measure 20.8 by 14.5, and 15.5 by 12.7 millimeters (Harris).

Incubation: F rank L. Burns (1905) writes:

Incubation does not always commence immediately after completion of set, particularly if the season be young. It is probable that the second night witnesses the beginning of that period and, as far as my experience goes, I believe it is performed by the female alone. The male feeds her when covering newly hatched young.

The home-coming of a brooding bird, after a brief airing and feeding, is heralded several hundred yards distant by frequent chips and short flights from branch to branch near the ground, in leisurely fashion and circuitous route, until at length, arriving above the nest, she runs down a sapling and is silent. The bird is a close sitter and if approached from the open front will often allow a few minutes’ silent inspection, eye to eye, at arm’s length, sometimes not vacating until touched, then she runs off in a sinuous trail, not always feigning lameness before the young are out. When disturbed with young in the nest she will flutter off with open wings and tail, and, failing to lead one off, will return with her mate, who is seldom far off at this period, circling about the nest or intruder, and, if the young are weli feathered, she will dash at them, forcing them from the nest and to shelter. Once this brave little bird dashed at me and ran up to my knee, scratching with her sharp little claws at every step. On the return the birds always make the vicinity ring with their protests: a quickly repeated chip. The period of incubation in one instance was thirteen days.

Young: Mr. Burns continues:

Young fear man soon after their eyes are open, and a menacing finger will cause them to scamper out and away, repeated replacing in the nest proving of no avail after they became panic-stricken. At three days of age they made no outcry but opened their mouths for food, which consisted of a species of white moth, or “miller,” and soft white grubs, supplied by either of the parent birds. At that period they were naked except a fluff on head and wing quills, just showing feathers at tips. In the presence of an intruder and absence of the parents, they will sit motionless if not threatened, and, but for the blinking, beady eyes, one might mistake them when well fledged, at very close range, for dead leaves. The head stripes became visible under the nestling down on the seventh day, and they left the nest ten days after leaving the shell, in the one case I have kept record of. The parents keep the young together for several days at least, just how long is impossible to say. One brood is all that is reared in a season, I think.

Plumages: Dr. Dwight (1900) calls the natal down “brownish mouse-gray,” and describes the juvenal plumage as follows: “Whole body plumage and the wing coverts cinnamon, palest on the abdomen. Wings and tail olive-brown edged with olive-green. Two indistinct lateral crown stripes brownish mouse-gray. A transocular streak dusky.” Ridgway’s (1902) description is somewhat different: “Head, neck, and under parts buff, the pileum with two broad, but strongly contrasted, lateral stripes of wood brown or isabella color; a postocular streak of the same color; back, scapulars, rump, and upper tail-coverts wood brown or isabella color; wing-coverts light buffy olive, the middle and greater broadly but not sharply tipped with cinnamon-buff; remiges and rectrices grayish olive-green, as in adults.” Young birds seem to vary considerably in the color of the upper parts.

A partial postjuvenal molt occurring in late June or early July involves all the contour plumage and the wing coverts but not the rest of the wings or the tail. The young bird in its first winter plumage is practically indistinguishable from the adult at that season, except for the juvenal wings, in which the tertials are lightly tipped with rusty brown.

There is apparently no spring molt, but a complete postnuptial molt occurs in July. Spring birds are slightly paler, grayer and less buffy than in the fall. The sexes are practically alike in all plumages.

Food: As I have said, the name worm-eating warbler seems to be somewhat of a misnomer for this bird. Edward H. Forbush (1929) writes: “I find no records of any consumption of earthworms by this species, which although a typical ground warbler spends some of its time hunting among the branches of trees, where it finds span-worms. It also hunts on the ground in damp places frequented by army-worms. Nevertheless these are not worms but caterpillars. Probably, however, in its perambulations and peregrinations upon the surface of the earth the bird now and then docs pick up a small earthworm, for earthworms form a staple food for many birds when the ground is moist.”

Arthur H. Howell (1924) says: “Little is known of the food of this species, but it seems doubtful whether it lives up to its name of ‘wormeater.’ Two stomachs of this bird from Alabama contained remains of weevils, beetles, bugs, caterpillars, and Hymenoptera.” Howell (1932) further reports: “The stomachs of three individuals taken in Florida in April contained small grasshoppers, caterpillars, sawfly larvae, beetles, and spiders. One dragon-fly, one bumblebee, and one ‘walking stick’ were also included in the contents.” Professor Aughey (1878) included the worm-eating warbler among the birds seen catching locusts in Nebraska.

Behavior: Brewster (1875) gives the best account of the activities of the worm-eating warbler as follows:

They keep much on the ground, where they walk about rather slowly, searching for their food among the dried leaves. In general appearance they are quite unique, and I rarely failed to identify one with an instant’s glance, so very peculiar are all their attitudes and motions. The tail is habitually carded at an elevation considerably above the line of the hack, which gives them a smart, jaunty air, and if the dorsal aspect be exposed, in a clear light, the peculiar marking of the crown is quite conspicuous. Seen as they usually are, however, dimly flitting ahead through the gloom and shadow of the thickets, the impression received is that of a dark little bird which vanishes unaccountably before your very eyes, leaving you quite uncertain where to look for it next; indeed, I hardly know a more difficult bird to procure, for the slightest noise sends it darting off through the woods at once. Occasionally you will come upon one winding around the trunk of some small tree exactly in the manner of Mniotilta varia, moving out along the branches with nimble motion, peering alternately under the hark on either side, and anon returning to the main stem, perhaps In the next instant to hop back to the ground again. On such occasions they rarely ascend to the height of more than eight or ten feet. The males are very quarrelsome, chasing one another through the woods with loud, sharp chirpings, careering with almost Inconceivable velocity up among the tops of the highest oaks, or darting among the thickets with interminable doublings until the pursuer, growing tired of the chase, alights on some low twig or old mossy log, and in token of his victory, utters a warble so feeble that you must be very near to catch it at all, a sound like that produced by striking two pebbles very quickly and gently together, or the song of Spizella soCiali8 heard at a distance, and altogether a very indifferent performance.

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 1% to 2% seconds in length. It is usually all on the same pitch, hut 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 0 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 c/zips. 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. XV. 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 wormeating 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 woodmice, 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.”

Friedmann (1929) regards the worm-eating warbler as a “rather uncommonly imposed upon species” by the eastern cowbird. “Twentyone definite records, and as many more indefinite ones have come to my notice.”

Winter: Dr. Alexander F. Skutch contributes the following: “‘Widely distributed as a winter resident in Central America, the worm-eating warbler appears to be everywhere very rare. It occurs from Guatemala to Panam4 on both coasts, and upward in the mountains to at least 5,000 feet. On February 20, 1935, I found one in the forest on Barro Colorado Island, Canal Zone, which appears to represent a slight southward extension of the known range. II have recorded this rare visitant from every part of Central America below 6,000 feet in which I have made an extended sojourn during the months of the northern winter, yet only one or two in each locality, except on the Finca MocA on the Pacific slope of Guatemala at 3,000 feet above sea-level, where in one day: January 21, 1935: I saw three. The worm-eating warbler is found in the Tropics beneath dense thickets or in the undergrowth of the forest, usually near the ground; but at times one will rise to the lower branches of the trees to investigate curled dead leaves caught up among them. It is solitary rather than social in its habits.

“The records of the occurrence of this warbler in Central America are too few to indicate clearly the dates of its arrival and departure. I found one at Tela, Honduras, on August 19, 1930; but the next early record is for October 14, at the same locality. Griscom quotes a record by Dearborn for the occurrence of this warbler at Patulul, Guatemala, on April 2; but except for this, the latest record I have seen is from El General, Costa Rica, March 11, 1939.”

DISTRIBUTION
Range: Eastern United States to Panama.

Breeding range: The worm-eating warbler breeds north to northeastern Kansas (Lawrence) ; possibly central southern Nebraska (Red Cloud) ; probably south-central Iowa (Des Moines) ; probably southern Wisconsin (Wyalusing, Madison, and Milwaukee); northeastern Illinois (Hinsdale); southern Indiana (Terre Haute, Bloomington, and Indianapolis); central Ohio (Columbus, East Liverpool, and possibly Cleveland); southern New York (Penn Yan and Albany), and southern Connecticut (New Haven and Saybrook). It has been found in sununer north to London, Ontario; Northampton, Ipswich, and North Easthain, Massachusetts. East to Connecticut (Saybrook); Long Island (Newtown); northern New Jersey (Elizabeth and Morristown); eastern Pennsylvania (Norristown and Philadelphia); northern Delaware (Wilmington); central Maryland (Baltimore; rarely east of Chesapeake Bay) ; eastern Virginia (Cobham and Dismal Swamp); central North Carolina (Chapel Hill and Statesyule); northwestern South Carolina (Caesars Head. Mount Pinnacle, and Sassafras Mountain); and northern Georgia (Brasstown Bald and Atlanta). South to northern Georgia (Atlanta); central Tennessee (Nashville and Wildersville) ; northern Arkansas (Newport and Winslow) ; and, occasionally, extreme northern Texas (Bowie County and Gainesville). West to northern Texas (Gainesville); northeastern Oklahoma (Jay) ; and eastern Kansas (Lawrence). It has been recorded in summer, but with no evidence of breeding, at Red Cloud, Nebr., and at London and Vineland Station, Ontario.

Winter range: In winter the worm-eating warbler is found north to southern Tamaulipas (Altamira) ; northern Florida, casually (Blue Springs and Amelia Island), and the Bahamas (Abaco, Nassau, and Great Inago). East to the Bahamas (Great Inago); Jamaica and central Panama (Rio Chepo). South to Panama (Rio Chepo, Barro Colorado, and Chiriquf). West to western Panama (Chiriquf); Costa Rica (Escas~~ and Volc~in Tonorio); El Salvador (Mount Cacaguatique) ; Guatemala (Duefias, Patulul, and Naranjo) ; southern Chiapas (Huehuetan); western Veracruz (Jalapa); Hidalgo (Pachuca); and southern Tamaulipas (Altamira).

Migration: Late dates of spring departure are: Panam~: Dari~n March 16. Costa Rica: El General, March 19. El Salvador: Barra de Santiago, April 8. Guatemala: Patulul, April 2. Yucatan: M~rida, April 9. Cuba: Habana, May 1. Bahamas: Abaco, April 29. Florida: Seven Oaks, May 14. Georgia: Cumberland, May 7. Alabama: Barachias, May 1. Mississippi: Biloxi, April 27. Louisiana: Avery Island, April 23.

Early dates of spring arrival are: Florida: Pensacola, March 26. Georgia: Savannah, April 4. South Carolina: Mount Pleasant, April 7. North Carolina: Bat Cave, April 16. Virginia: Richmond, April 19. West Virginia: Morgantown, April 4. District of Columbia: Washington, April 21. Pennsylvania: Beaver, April 29. New York: Jones Beach, April 20. Louisiana: Grand Isle, April 3. Mississippi: Bay St. Louis, April 5. Tennessee: Chattanooga, April 15. Kentucky: Bowling Green, April 3. Indiana: Brookville, April 17. Ohio: Columbus, April 18. Texas: Brownsville, March 29. Missouri: St. Louis, April 15. lowa: Keokuk, April 21.

Late dates of fall departure are: Missouri: St. Louis, September 20. Ohio: Austinburg, September 23. Kentucky: Middlesboro, September 27. Tennessee: Athens, October 5. Mississippi: Biloxi, October 11. Louisiana: Monroe, September 30. New York: Balston; September 23. Pennsylvania: Atglen, October 10. District of Columbia: Washington, September 13. West Virginia: Bluefield, September 19. Virginia: Salem, October 24. North Carolina: Andrews, October 11; Raleigh, November 3. South Carolina: Charleston, October 11. Georgia: Atlanta, October 10. Florida: Fernandma, October 3.

Casual records: A specimen was collected in Bermuda on October 4, 1899. An individual was present at Wood Pond near Jackson, Somerset County, Maine, September 1 to 12, 1935; and one was reported seen at Mayagiiez, Puerto Rico, on October 15, 1943, following a small hurricane.

Egg dates: Connecticut: 7 records, May 27 to June 29.

New Jersey: 4 records, May 21 to 30.

Pennsylvania: 75 records, May 15 to June 30: 45 records, May 24 to June 5, indicating the height of the season (Harris).