Dull in plumage but persistent and musical in song, the Warbling Vireo has a large breeding range across North America. Warbling Vireos occupy forests as well as human dominated landscapes such as parks and suburbs. Migration takes place at night, and one study found that young vireos migrating south spent about three days at a stopover site along the way.
Female Warbling Vireos sometimes sneak into a neighboring pair’s territory to steal material from their nest. Rates of nest parasitism by Brown-headed Cowbirds are generally high, reaching eighty percent in one study, and most nests with cowbird eggs end up not raising any vireos.
On this page
Description of the Warbling Vireo
The Warbling Vireo is a medium-sized vireo with a pale gray head, greenish-gray upperparts, pale underparts, and a faint dark line through the eye with white above and below.
Seasonal change in appearance
Juveniles are similar to adults.
Warbling Vireos inhabit mixed and deciduous woodlands, and small groves near water.
Warbling Vireos primarily eat insects, but also berries.
Warbling Vireos glean insects from leaves, often high in trees.
Warbling Vireos breed from west-central Canada south throughout most of the U.S. except the southeast. They winter in Mexico and Central America. The population has increased in recent decades.
Warbling Vireos are often parasitized by Brown-headed Cowbirds.
The Warbling Vireo is capable of puncturing a cowbird egg to eject it from a nest, and may be the smallest songbird able to do it.
The typical song is a fast series of whistled phrases.
- Red-eyed Vireos have a much stronger face pattern and a darker head with more contrast between the head and upperparts.
The Warbling Vireo’s nest is a compact cup of bark strips, grasses, and other fine materials, and is woven into the fork of a horizontal branch.
Number: Usually lay 3-4 eggs.
Color: White with darker markings.
Incubation and fledging:
The young hatch at about 12-14 days and fledge at about 13-14 days, though remaining dependent on the adults for some time.
Bent Life History of the Warbling Vireo
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 Warbling Vireo – the common name and sub-species reflect the nomenclature in use at the time the description was written.
VIREO GILVUS GILVUS (Vieillot)
HABITSCONTRIBUTED BY WINSOR MARRETT TYLER
The warbling vireo, if it were not for its song, would not be a notable species, for it is a little bird in leaf-green plumage, inconspicuous as it moves about among the foliage on the highest branches of its favorite elms and poplars where it spends the summer days, surrounded by green leaves and almost hidden by them.
High up in the trees, one of its nearest neighbors is the wood pewee, another leafy-green little bird. But unlike the pewee that sits motionless on its perch, flying out from it now and then into the air to catch its prey, the vireo rambles about among the leafy branches, finding its food there.
Spring: When the warbling vireos arrive in New England early in May, we of their human friends hope that a pair will settle in the roadside trees near our homes, for if they do, although we may rarely see them, we know that the male will entertain us with his delightful song, filling the days with charming, simple melody all through the summer, even on the hottest days of July and August.
The song, as it goes on hour after hour, suggests a spirit of quiet happiness, a contrast to the flaunting, martial bugling of the Baltimore oriole, another of the vireos’ neighbors, and to the slow, sweet notes of the wood pewee with their hint of pathos. In the vireo’s song there is an air of unhurried calm, a leisureliness we seldom hear in the voice of a bird. Spring brings us greater artists, more proficient technicians, birds of more exuberant joyousness, but no such comfortable and welcome “guest of summer” as the warbling vireo.
Courtship: We know little in detail of the nesting activities of the warbling vireo, for the bird stays so high above the ground at this season that we rarely see him at short range. Audubon (1842), however, by a fortunate chance, was able to watch the building of a nest under favorable circumstances, and noted a bit of courtship behavior of which he remarks: “During the love days of the pair mentioned above [see below under nesting], the male would spread its little wings and tail, and strut in short circles round the female, pouring out a low warble so sweet and mellow that I can compare it only to the sounds of a good musical box. The female received these attentions without coyness, and I have often thought that these birds had been attached to each other before that season.” Audubon also mentions the odd, swaying motion which is characteristic of the red-eyed vireo (q. v.) both in the season of courtship and after the young are fledged. He says: “I observed that they now and then stood in a stiffened attitude, balancing their body from side to side on the joint of the tarsus and toes, as on a hinge, but could not discover the import of this singular action.”
Nesting: Dr. Thomas M. Brewer (Baird, Brewer, and IRidgway, 1874), speaking of the nests, says:
The Warbling Vireo builds its nest osually in more elevated positions than any others of this family. For the most part in the vicinity of dwellings, often over frequented streets, they suspend their elaborately woven and beautiful little basket-like nest, secure from intrusion from their human neighbors, and protected by the near presence of man from all their more dreaded enemies.
The nests of the Warbling Vireo, while they resemble closely those of the other species in all the characteristics of this well-marked family, are yet, as a rule, more carefully, neatly, and closely built. They are usually suspended at the height of from thirty to fifty feet, in the fork of twigs, under and near the extremity of the tree-top, often an elm, protected from the sun and storm by a canopy of leaves, and just out of reach of most enemies. They vary little in size, being about two inches in height and three and a half in their greatest diameter, narrowing, toward their junction with the twigs, to two inches. They are all secured in a very firm manner to the twigs from which they are suspended by a felting of various materials, chiefly soft, flexible, flax-like strips of vegetable fibres, leaves, stems of plants, and strips of bark. With these are interwoven, and carried out around the outer portions of the nest, long strips of soft flexible bark of deciduous trees. They are softly and compactly filled in and lined with fine stems of plants.
William Brewster (1906) writes: “The nest of the Warbling Vireo is ordinarily built at least thirty or forty feet above the ground, at the end of a long, slender branch. Silver-leaved poplars are preferred to all other trees, but where these are not available the birds content themselves with large, spreading white ash trees, or with elms, lindens or maples, while they occasionally choose apple or even pear trees.”
A. C. Bent (MS.) writes of a nest which he collected “25 feet from the ground in the top of a pear tree, attached to some small, leafy twigs close to an outer, topmost branch. The nest was deeply hollowed and well made of strips of inner bark of shrubs, various soft fibers, leaves, feathers, spiders’ nests and cobwebs; it was lined with fine grasses and horse hair.” And Cones (1878) points out that “the nest is quite deeply cupped, with a somewhat contracted brim, for the still greater safety of its precious freight.”
M. G. Vaiden (MS.), of Rosedale, Miss., sends to Mr. Bent the following data on nests of the warbling vireo: “A nest 60 feet from the ground, out on a limb, in a crotch of a small limb branching from a larger one. However, the nest was only 14 feet from the trunk of the tree. The nest was very similar to that of the red-eye vireo, but a little heavier material had been used, and there was less workmanship on the outer side, not so much inner bark strips or nioss, although there was a dab here and there.” Another nest: “At the very top outer branciles of a pecan, 90 feet high.” A third nest: “In young sycamore tree, out on limb and semipensile, not over 15 feet from the ground on a branch over a little-used dirt road. This was the tallest tree (20 feet) in the vicinity..” And A. Dawes Du Bois (MS.) sends the following: “About 40 feet from the ground in top of willow tree on bank of river; about 40 feet up in red oak tree 30 yards from our house; 10½ feet from the ground in apple tree in orchard.” Of the second nest he says: “While I was watching the singing bird on the nest, his mate caine and replaced him. The change was made as quick as a flash; as he slipped off the nest, his mate slipped instantly into it. A rather stiff wind was blowing, so that the eggs would not have been safe for half a second if left uncovered. However, I found later that, even when there was no wind, the birds changed places rather quickly.”
Audubon (1842) gives an account of the building of a nest in a Lombardy poplar which almost touched his window. He says:
Never before had I seen it placed so low, and never before bad I an opportunity of examining it, or of observing the particular habits of the species with so much advantage. The nest, although formed nearly in the same manner as several others, which I have since obtained by cutting them down with rifle balls, from the top twigs cC tho tall trees to which they were attached, Instead of being fastened in the fork of a twig, was fixed to the body of the tree, and that of a branch coming off at a very acute angle. The birds were engaged In constructing it during eight days, working chiefly in the morning and evening. * * * One morning I observed both of them at work; they had already attached some slender blades of grass to the knots on the branch and the bark of the trunk, and bad given them a circular disposition. They continued working downwards and outwards, until the structure exhibited the form of their delicate tenement Before the end of the second day, bits of hornets’ nests and particles of cornhusks had been attached to it by pushing them between the rows of grass, and fixing them with silky substances. On the third day, the birds were absent, nor could I hear them anywhere in the neighborhood, and thinking that a cat might have caught them from the edge of the roof, I despaired of seeing them again. On the fourth morning, however, their notes attracted my attention before I rose, and I had the pleasure of finding them at their labours. The materials which they now used consisted chiefly of extremely slender grasses, which the birds worked in a circular form within the frame which they had previously made. The little creatures were absent nearly an hour at a time, and returned together bringing the grass, which I concluded they found at a considerable distance. Going into the street to see in what direction they went, I watched them for some time, and followed them as they dew from tree to tree toward the river. There they stopped, and looked as if carefully watching me, on which I retired to a small distance, when they resumed their journey, and led me quite out of the village, to a large meadow, where stood an old hay-stack. They alighted on it, and in a few minutes each had selected a blade of grass. Returning by the same route, they moved so slowly from one tree to another, that my patience was severely tried. Two other days were consumed in travelling for the same kind of grass. On the seventh I saw only the female at work, using wool and horse-hair. The eighth was almost entirely spent by both in smoothing the inside. They would enter the nest, sit in it, turn round, and press the lining, I should suppose a hundred times or more in the course of an hour. * * * In the course of five days, an equal number of eggs was laid.
Eggs: [AUTHORS’ NOTE: The warbling vireo lays three to five eggs to a set, usually four. These are practically ovate and without any appreciable gloss. They are pure white, with only a few scattered spots of various shades of reddish or darker browns, or blackish, the darker spots being commonest. The measurements of 50 eggs average 19.1 by 14.2inillimeters; the eggs showing the four extremes measure 20.3 by 14.7, 18.7 by 15.1, 17.8 by 13.6, 18.8 by 13.2 millimeters.] Young: We meet the young warbling vireos at close range when they come down from their lofty nest and follow their parents about in the shrubbery. They are odd, pale little birds when we first see them in July, not long from the nest: light brown on the back, with a wash of yellow on the breast and flanks, and hoary about the head, almost white, although they soon lose this latter mark. A. Bawes Du Bois (MS.) remarks: “The plumage of the fledglings is so pale that they look like little white birds.” The old birds feed them with larvae (often a long, green worm),large moths (after pulling off the wings), and later, when the shrubs have fruited, with cornelberries.
The young birds at this time, as well as the adults, give a curious note which attracts our attention to these family gatherings. It strongly suggests the distant clipping of garden shears: a sort of sneeze.
Audubon (1842) gives the incubation period as 12 days, and says of the young birds: “On the sixteenth day after their exclusion from the egg, they took to wing, and ascended the branches of the tree, with surprising ease and firmness.”
Plumages: [Au’rHoa’s ~om: Dr. Dwight. (1900) calls the natal down “pale wood-brown” and describes the juvenal plumage as “above wood-brown, very pale on pileum and nape, darker and faintly tinged with olive on the back. * * * Below, white, the crissum tinged with pale primrose-yellow. Auriculars, orbital ring and superciliary line white.”
There is a partial postjuvenal molt, beginning early in August, which involves the contour plumage, and the wing coverts, but not the rest of the wings nor the tail. This produces a first winter plumage which is practically indistinguishable from the winter plumage of the adult, greener above and more buffy white below than the previous plumage.
Dr. Dwight says that the nuptial plumage is acquired by wear, but Ned Dearborn (1907) found March and April specimens of the western race undergoing a scattered molt on the head and breast. This may also be true of other vireos, though we have not the proper specimens to show it.] Food: In his study of food habits of the vireos, Dr. Edward A. Chapin (1925), summarizing his findings, says:
The economic status of the warbling vireo is in some ways more distinctly unfavorable than that of the other species of this family of birds, especially In its consumption of ladybirds. In more than a third of the stomachs examined the remains of these beneficial beetles were found. * * * On the other band, the Injurious insects taken by the warbling vireo make up the greater part of the food. Lepidopterous remains, Including adult moths and butterflies, caterpillars, pupae, and eggs, were taken from about 77 per cent of those examined. This alone should atone for the bird’s Injurious proclivities along other lines. * Little If any of the vegetable food taken was obviously cultivated, In most cases being from plants not used for their fruits. It seems reasonable, then, to class the bird as neither beneficial nor injurious.
Elliott Coues (1878) adds an interesting food item. He says in a footnote: “Prof. Samuel Aughey gives the Warbling Vireo among the birds of Nebraska which destroy the scourge of that country: the grasshopper,” quoting him as follows: “‘I frequently saw it light down within a rod of me where locusts abounded and feed on them. This species seemed to eat them in all stages of their growth, and brought them constantly to their nests for their young.~ Tilford Moore writes to Mr. Bent that he has several times seen one hang upside down from a twig to get food out of an apple blossom.
Behavior: William Brewster (1906), writing of the bird in eastern Massachusetts, says: “The warbling vireo is a bird of somewhat peculiar and restricted distribution. It shuns extensive tracts of woodland and, indeed, most wild and primitive places, although it nests sparingly in orchard or shade trees near secluded farmhouses, and rather frequently along country roads bordered by rows of large elms or maples. We find it most commonly and regularly, however, in or near village centers such as those of Lexington, Arlington, Belmont and Watertown.~~ Mr. Brewster is referring here to the early years of this century. I remember that in those days I used to hear warbling vireos about half a mile apart along the main street through Lexington, but before many years, about 1912, we noted a diminution in their numbers; every year fewer and fewer breeding pairs returned, until, early in the 20’s, the species became practically unknown in the town, and was rare throughout eastern Massachusetts. However, since about 1938, there has been a decided increase in its numbers.
The warbling vireo is so partial to the lines of trees along our village streets and to isolated trees in open country that, thinking back to the time when this land was covered chiefly by unbroken forest, we wonder where the bird could have found in those days a habitat to its liking. It is thought that the well-watered trees on the border of the broad lanes opened by rivers through the forest were the former habitat of the bird, for these would afford a situation not unlike the vireos’ present breeding ground. Aretas A. Saunders (1942) expresses this conjecture: “I believe that the warbling vireo originally inhabited trees along stream borders. With the coming of civilization, shade trees along city streets formed a rather similar habitat, and it adopted such places. This will explain its preference for elms and silver maples, trees that originally were found along stream borders.”
In former times, apparently, the warbling vireo was a resident in large cities. Dr. Brewer (Baird, Brewer, and Ridgway, 1874) says: “It is especially abundant among the elms on Boston Common, where at almost any hour of the day, from early in the month of May until long after summer has gone, may be heard the prolonged notes of this, one of the sweetest and most constant of our singers.” Henry D. Minot (1895), speaking of the 1870’s, also mentions the birds’ occurrence “among the elms of Boston Common.”
Many observers have noted the warbling vireo’s habit of singing while he is incubating. William Brewster (1937) speaks of it thus: “Soon after leaving the Yellow-throat’s nest, I heard our Warbling Vireo singing in the orchard. Thinking that he might be on the nest, I followed up the sound and directly saw the nest in the very top of a rather tall tree attached to the horizontal twigs of a long, upright leafy branch. I could see the bird’s head distinctly. lie raised it high when he sang and his white throat swelled and flashed in the sunlight.”
Francis H. Allen (MS.) describes an unusual observation: “I once saw a pair perched in bushes and low trees on a river bank and flying frequently down to the surface of the stream, striking it forcibly, and then returning to their perches, where they preened their feathers. Both birds participated, but not simultaneously. Whether the purpose was for bathing or to take insects from the surface of the water I could not make out, but, intentionally or not, they got their baths. In all cases it was a straight dash to the water at an angle of perhaps 25 or 30 degrees.”
Voice: Wherever we turn in the literature of the warbling vireo we find that the author, after commenting on the bird’s inconspicuousness, speaks enthusiastically of its song, pointing out the difference from the songs of the other vireos, the length of the song period, and the charm of the smoothly flowing warble.
The song of the warbling vireo is not broken up into short, exclamatory phrases like those of the other common New England vireos, the red-eyed, the solitary, and the yellow-throated, but continues on in a long series of slow, quietly delivered musical notes increasing in force to the end. The pitch undulates gently to the final note, which is generally the highest and the most strongly accented. Some writers find a resemblance in the song to that of the purple finch, but the finch’s notes are very rapid and energetic and have none of the calm deliberateness of the vireo’s melody. The most suggestive rendering of the vireo’s song, perhaps, is Wilson Flagg’s (1890) “Brig-a-dier, Brig-a-dier, Brigate,” which, pronounced slowly, brings out the rhythm admirably.
Aretas A. Saunders (MS.) sends to Mr. Bent this summary of the song: “The song of the warbling vireo consists of a series of connected notes, with no two consecutive notes on the same pitch, and is therefore a true warble. Individuals often sing several different songs, and in a number of cases I have recorded from three to seven different songs from one individual. The pitch varies from D ”’ ‘to C 4 ” ‘,half a tone more than an octave. The average song ranges about 31/2 tones in pitch. Songs consist of 7 to 25 notes each and vary in length from 1 to 3 seconds. The notes are not all the same length. A common form is made up of one long note followed by two short ones, and when this is repeated several times it is like dactylic feet in poetry. It is common for the song to end on a high note.”
In the summer of 1912 a bird t.hat was breeding on Lexington Common, within hearing from my windows, showed a marked departure from the normal song. My notes say: “He often utters a part of his song in a squeaky voice with no whistled quality whatever, the tone becoming so high that it contains a sibilant sound. Sometimes he changes to the squeak in the middle of the song, returning to the whistle before the end; sometimes he ends with the squeak.” Strange to say, later in the same year I heard a similar song from another warbling vireo breeding 5 miles from Lexington. This variation, however, must be rare, for I have not heard it since, although I have heard the red-eyed vireo sing in this manner.
The bird often sings until well into September: Mr. Bent has heard it singing daily from August 31 to September 13, inclusive, and my records for 10 years average August 27, the latest being September 18, 1910.
The warbling virco has two common minor notes; one the sound that resembles the sharp clipping of garden shears, mentioned under “Young,” and a complaint note, corresponding, apparently, to the qu~ee of the redeye, but with no downward inflection. It is a hard, tense snarl, with sometimes a slight upward inflection, easily recognized as a diagnostic note of the species.
Dr. Jonathan Dwight, Jr. (1897), makes an interesting comment on this latter note. Speaking of a similar note of the Philadelphia vireo, he says: “It does not resemble the corresponding complaint note of olivaceus, but is almost exactly like the aggressive m4~ci of gilvus, which has a suggestion of the katydid about it.”
Tilford Moore says in his notes: “Today I saw one singing in flight; he finished his song just after alighting but sang three-quarters of it in flight.”
Field marks: The warbling virco has no mark in its plumage that enables us to identify it at a glance as a species. It has no wing bars, no eye ring, no distinctive lines on the head, like some of the other vireos: it is merely a gray-green little bird, but, from the shape of its bill and its manner in moving about, clearly a vireo. So we have to come to an identification by elimination, by the process of reductio ad absurdum.
Yet, before long, when we have seen the bird time and time again, it begins to take on an individuality of its own, as all birds do when we learn to know them well, and we recognize it, not, as we recognize many birds, by some pcculiarity of plumage, not even because it lacks any distinctive marks, but. because it suggests the definite personality we have attributed to the warbling vireo. The side of the head, marked only by a slight paleness above the eye, has an expression of bland innocence; the delicate coloring of the plumage, with no spot of ornament to set it off, gives an air of quiet refinement, like the bird’s song; and the diminutive bill gives the bird a youthful appearance.
Enemies: Ilerbert lTriedmann (1929) says of the relation of the cowbird to the warbling vireo: “A very common victim. * * ï Eaton lists the Warbling Vireo as one of the commonest molothrine victims in New York State, and I have numerous records from other parts of the country. * * * All together over forty records have come to my notice. In common with the other species of its family, this Yireo normally makes no attempt to rid herself of the parasitic eggs.” In recent year the warbling virec has probably suffered more from the spraying of the shade trees with poison than from the natural enemies that commonly beset small arboreal birds. Their nests have been imperiled by the high-pressure spraying that rocks the elm branches at the vital points of the birds’ summer distribution, the roadside trees of our country towns.
Winter: Donald R. Dickey and A. J. van Rossem (1938) speak of the bird on its winter quarters:
The winter home of the eastern warbling vlreo can now be stated to be In the foothills of El Salvador and adjacent parts of Central America. * On Mt. Cacaguatique In late November and in December, 1925, warbling vireos were abundant at 2,500 feet elevation, all through the berry-bearing trees which provided shade for the coffee groves. From there up to the oak- and pine-covered summit of the mountain (about 4,000 feet) they were also very numerous. In February and March, 1926, both on Volcdn de Conchagua and Volcdn de Sau Miguel numbers were observed in similar environments at from 2,500 to 3,500 feet, but much less commonly than in the interior. At Chilata In April, 1927, warbling vireos were migrating and were usually In pairs.
Ludlow Griscom (1932) writes: “It is apparently quite common and generally distributed in Guatemala in winter, arriving principally in October, the earliest date being September 28, 1920.”
Range: Canada to El Salvador.
Breeding range: The warbling vireo breeds north to northern British Columbia (Atlin, Fort Halkett, and Fort Nelson); southwestern Mackenzie (Wrigley, Simpson, Providence, and Resolution); northeastern Alberta (Chippewyan and McMurray) ; central Saskatchewan (Wingard and Prince Albert) ; southern Manitoba (Duck Mountain, Lake St. Martin, and Selkirk; probably to Norway House); southern Ontario (Port Arthur, Lake Nipissing, and Ottawa); southern Quebec (Montreal and Quebec) ; southern New Brunswick (Fredericton); Prince Edward Island (Brackley Point); and Nova Scotia (Pictou). East to central Nova Scotia (Pictou, Truro, and Halifax) ; the Atlantic coast of the United States to southern Virginia (Dismal Swamp); through the mountains to northern Alabama (Anniston and Florence). South to northern Alabama (Anniston); western Mississippi (Shell Mound and Rodney); southern Louisiana (New Orleans, Houma, and Calcasieu); sparingly in southern Texas Huntsville, Rockport, Marathon, and the Guadalupe Mountains); southern New Mexico (Cloudcroft, Silver City, and the Animas Mountains); southwestern Chihuahua (Bravo and Mina Abundancia); central Sonora (Rancho Santa Barbara and Magdalena); and southern California (Santa Ysabel and Escondido); also resident in the Cape region of Lower California. West to the Pacific coast of California (Escondido, Santa Barbara, San Francisco, and Eureka); Oregon (Grants Pass, Eugene, Tillamook, and Astoria); Washington (La Push, Cape Flattery, and Bellingham) ; and British Columbia (Victoria, Cape Scott, Kimsquit, Great Glacier, Telegraph Creek, and Atlin).
Winter range: In winter the warbling vireo is found from southern Veracruz (Orizaba) through southern Oaxaca (Tehuantepec) ; southcentral Chiapas (Comitfin); western Guatemala (Finca Carolina, Sacapula, Patulul, and Progreso); to El Salvador (Colimas and Mount Cacaguatique).
The above range includes all the subspecies of the warbling vireo breeding within the Check-list range of which four are recognized. The typical race, the eastern warbling vireo (V. g. gilvu8), breeds west to eastern Saskatchewan and the eastern edge of the Great Plains and northern Texas. The Oregon warbling vireo (V. g. leucopolius) breeds from northern British Columbia (except the coastal area) and southwestern Mackenzie south to northern Nevada and Montana. The western warbling vireo (V. g. swainsoni) breeds in the coastal region of British Columbia, Washington, and Oregon, through southern Nevada, to southern Wyoming and Colorado, and south to southern California and western Texas. The Cape warbling vireo (V. g. victoriae) breeds in the Cape district of Lower California. Additional races occur in Mexico.’ Migration: L ate dates of spring departure from the winter home are: El Salvador: Chilata, April 27. Guatemala: Patulul, April 2. Veracruz: Presidio, May 4.
Early dates of spring arrival are: Alabama: Syllacauga, April 16. Georgia: Macon, April 16. North Carolina: Asheville, April 13. District of Columbia: Washington, April 21. Pennsylvania: ‘The subspecies leucopelies and victsriae were officially recognized by the A. 0. U. cornmitee after tbe manuscript of this bulletin was submitted; hence no separate accounts of them are here lncluded: flnsTua. Pittsburgh, April 24. New York: New York, April 28. Massachusetts: Marlboro, April 27. New Hampshire: East Jafirey, April 27. Maine: Augusta, May 1. Quebec: Montreal, May 16. Louisiana: Chenier au Tigre, March 4. Arkansas: Rogers, April L Missouri: St. Louis, April 6. Kentucky: Guthrie, April 5. Indiana: Bloomington, April 21. Michigan: Ann Arbor, April 21. Ohio: Columbus, April 19. Ontario: London, April 29. lowa: Keokuk, April 24. Wisconsin: New London, April 28. Minnesota: Red Wing, May 2. Manitoba: Aweme, May 15. Texas: Palmetto Park, March 31. Oklahoma: Oklahoma City, April 16. Kansas: Manhattan, April 18. South Dakota: Yankton; April 25. North Dakota: Fargo, May 11. Saskatchewan: Indian Head, May 12. Colorado-Colorado Springs, May 1. Wyoming: Careyhurst, May 10. Montana: Corvallis, May 6. Alberta: Glenevis, May 1. Mackenzie-ilSimpson, May 22. Anzona: Yuma, March 12. Utah: Provo, May 11. Idaho: Coeur (l’Alene, May 3. California: Los Angeles, March 11. Oregon: Eugene, April 12. Washington: Prescott, April 26. British Columbia: Hastings, April 26; Atlin, May 18.
Late dates of fall departure are: British Columbia: Atlin, August 17; Courtenay, September 17. Washington: Yakima, September 19. Oregon: Coos Bay, September 20. California: Berkeley, October 3. Alberta: Glenevis, August 20. Montana: Fortine, September 9. Wyoming: Yellowstone Park, September 29. Colorado: Fort Morgan, September 18. Saskatchewan: Indian Head, September 23. North Dakota: Argusville, September 21. South Dakota: Yankton, September 30. Nebraska: Red Cloud, October 1. Oklahoma: Kenton, September 22. Texas: Brownsville, October 2. Manitoba: Aweme, September 19. Minnesota: St. Paul, September 26. Wisconsin: Racine, October 7. Missouri: St. Louis, September 27. Illinois: Chicago, September 27. Ontario-Ottawa. September 22. Ohio: Toledo, October 11. Tennessee-Knoxville, October 10. Arkansas: Helena, October 5. Maine: Dover-Foxeroft, October 5. Vermont: St. Johnsbury, September 29. Massachusetts: Taunton, October 1. New York: Schenectady, October 1. Pennsylvania: McKeesport, October 7. District of Columbia: Washington, September 12. Georgia: Augusta, October 15.
At a banding station at Northville, S. Dak., 41 warbling vireos were banded over a period of 4 years and four individuals were retrapped in subsequent years:
Banded June 11, 193~ August 4, May 30, 1932 June 12, May 17, 1933 May 20, 1August 20, 1933 – May 21, 1934
Egg dates: California: 82 records, April 26 to July 25; 41 records, May 24 to June 14, indicating the height of the season.
Massachusetts: 11 records, May 20 to June 25; 7 records, May 26 to June 8.
New York: 33 records, May 20 to June 25; 23 records, May 25 to June 6.
Washington: 15 records, May 22 to June 29, 10 records, June 15 to 22.
WESTERN WARBLING VIREO
VIREO GILVUS SWAINSONI Baird
The western warbling vireo differs from the eastern race by being smaller, with a relatively smaller bill; “coloration darker, especially the pileum, which is perceptibly (often distinctly) darker than the back; the latter, together with the sides and flanks, usually more strongly olivaceous,” according to Ridgway (1904).
It is a widely distributed and very common bird in all suitable localities in the Western States and southern Canada, from the Great Plains to the Pacific slope. It seems to be equally common in the valleys, in the wooded canyons, or in the mountains, up to 6,500 feet in northern Montana and up to 10,000 feet farther south. It lives wherever it can find deciduous trees and shrubbery, showing a decided preference for cottonwoods and aspens. In most places its haunts are in the wilder, uninhabited regions, along the banks of streams and on the edges of woodlands and clearings. But S. F. Rathbun tells me that near Seattle, Wash., it is also found “about the cities and towns, building its nest in some shade tree along the street.” He says t.hat at Lake Crescent, Wash., it is “restricted to, or in the vicinity of, the deciduous growth near the lake, or along its shore. ïWherever there was a clearing in which might grow the western maple, here would probably be found a pair of the vireos. In some of the wilder parts of the region, particularly the river valleys that are bordered with a deciduous growth of alders and cottonwood, it will be found very common; and in such localities the flow of its song, mingled with the murmur of the running stream, is most pleasing to hear.”
Russell K. Grater tells me that, in Zion National Park, Utah, it “is a very common summer resident in t.he broadleaf trees along the canyon floor and up to elevations around 7,000 feet.” Howard L. Cogswell writes to me, from Los Angeles County: “In the breeding season here, the warbling vireo is chiefly a bird of the mountain canyons, or more definitely of the riparian growth (alders, cottonwoods, sycamores, and maples) along the streams from the tree filled gulches in the foothill mesas barely into the lower edge of the pine belt.” Dr. Jean M. Linsdale (1938) says that, in the Toyabe Mountains, in Nevada: the warbling vireo was one of the common species, widespread wherever there were deciduous trees. It was of regular occurrence in the groves of aspens and cottonwoods. The favorite habitat was in trees 25 to 80 feet high where there was some undergrowth and leaf litter. But the birds kept closely within the crown foliage. This was the most numerous species in the birches and willows which lined the streams. It occurred also, but less commonly, over the ridges in mountain mahoganies. Chokecherry thickets provided suitable homes, especially when in fruit in the fall. Individuals were seen a few times In pifions. * * * One was singing in bushes of Sy;nphortcarpos on an east-facing ridge at 8600 feet near Kingston Creek. The nearest trees were mountain mahogany, 200 to 800 yards distant.
Spring: The western warbling vireo evidently occurs mainly as a migrant, in Guatemala, for Ned Dearborn (1907) says: “One was taken and another seen at El Rancho January 6th. No more were seen until March 24th, when they were found at Patulul in abundance, and so continued, at least, until April 2d. Seven were collected at Patulul. At this time, they were passing through the trees in loose flocks and were evidently migrating. The March and April specimens were undergoing a scattered moult, not a general renewal, on head and breast.”
Mr. Cogswell says in his notes: “During the spring migration in April and early in May, warbling vireos are quite common throughout Pasadena, Calif., especially sections with oaks and sycamores. Many migrants sing constantly during their stay of a few hours or a day or so in one vicinity.”
Mr. IRathbun (MS.) says of the spring migration in western Washington: “At first a few in company will be seen, these little birds seeming to pass on. Often a day or two elapses before any more are seen~ then once more a few pass by. This is followed by the appearance of numbers of the vireos, after which the species is common and will be found in its accustomed places. This movement seems to be covered by a period of about 15 days.”
Nesting: Mr. Rathbun tells me that he finds the nests of the western warbling vireo in maples, alders, and other deciduous trees from 4 to 40 feet above ground, “but, as a rule, one can expect to find them at some considerable height.” He gives me this good description of a nest: “This nest was attached in the usual way to a fork of one of the branches of a young alder tree, which grew at the edge of a clump of the same kind of growth, the nest being suspended only six feet above the ground. Its construction represented the ordinary cup-shaped nest made by most vireos, and the materials used were similar except in one marked respect; the outside of this nest was almost entirely of the dingy-gray, cottony substance from the black cottonwood tree, this material held in place by means o} long blades of green grass; and there was also tied on the outer side a green alder leaf. Some of the blades of grass completely encircled the nest, aiding its attachment to the fork from which it hung, and, together with spider webs, were used to hold the cottony substance in place. The nest was a beautiful object and harmonized so well with its natural surroundings that it would easily escape notice among the glimmering alder leaves. And so much cottony substance had been used on the outside of the nest that in spots it was fully one-half inch in thickness. This nest was neatly lined with very fine shreds of the outer bark from dry weed stalks; and filaments of spider webs were also utilized to bind the edge of the nest to the fork from which it hung.”
Dr. Linsdale (1938) reports four Nevada nests; one was 8 feet up in a chokecherry near the base of a rocky cliff at 8,000 feet altitude in a canyon; and another, found the same day, was 15 feet above ground in an aspen in the same vicinity. Two others were 15 feet above ground in a birch clump and 9 feet up in an aspen, respectively. Frank C. Willard (1908) found a nest in Arizona that was 30 feet from the ground in a sycamore in a canyon.
Grinnell and Storer (1924) report two nests in the Yosemite Valley; one was “41,4 feet above the ground at the forking of two almost leafless branches of a coffee berry bush.” The other was about 12 feet up and 3 feet out from the trunk of a young black oak. Dr. Grinnell (1908) found a nest 6 feet feet from the ground in an apple tree in the San Bernardino Mountains, and several others in cottonwoods, from 6 to 20 feet above ground.
The best account I can find of the nesting and home of the western warbling vireo is that published by Henry J. Rust (1920), of Coeur d’Alene, Idaho.
His first nest “was suspended from the fork of a small spiraea bush, five feet from the ground, back about ten feet in dense shrubbery along an old roadway”; this nest was torn down and destroyed when the young were about 8 days old. But he found another nest the following year along the same roadway, and watched the birds building it and rearing their young successfully. He took a number of good photographs of it (pls. 46, 47). It was 4’/2 feet from the ground in a fork of a small willow, and, when first found, “consisted of several blades of dry grass woven over and under, back and forth across the crotch, the loose ends drooping, with several bits of willow down adhering.” He continues:
In the afternoon of the next day the rim was finished and rounded out in shape to support the completed nest; some of the loose ends were woven In and out, with a few additional dry grass stems, bits of string and willow down, this forming a part of the body of the nest. Two days later, the 27th, the nest was completed on the outside. When visited on the 30th the lining was In place, consisting of dry grass stems interwoven with ten or twelve strands of horse hair. The nest as completed measured as follows: Diameter outside, 2’4 by 3 Inches; length 3 inches; diameter inside, 1’A2 by 2 Inches; depth 1% Inches.
On dissecting the nest after the young had flown, the following materials were rioted, besides the dry grass blades and stems already mentioned: Three pieces of white string, 14, 15, and 24’A inches in length, respectively; also a number of small white threads of various lengths up to 6½ inches; 35 detachable bits of down from willow seeds, with many woven in securely; several bits of lichen (Alectorla fremontii) ; small strips of ninebark (Opulaster paucifiorus) ; three small pieces of old discolored cotton; and, in the rim, bits of matted cow hair. There being four houses less than one hundred yards from the nesting site, the string, horsehair and cotton were no doubt obtained on or near those premises. The balance of the material could have been secured a few feet from the nest. In weaving the long piece of string, one end must have dropped down, and in picking up the loose end it had been passed under a small twig below the nest, forming a long hanging loop that remained in place during the occupancy of the neat, as shown in the photos.
The hulk of the nest, if not the entire structure, was built by the female. The male remained in nearby trees, singing at regular intervals, but he was not noted helping at any time. As in the case of the former nest, several days passed after it was finished before any eggs were laid. The first egg in the second nest was noted on June 4. Visited late in the afternoon of the 7th, the nest contained four eggs, the complete set.
The young willow in which the nest was placed was growing in a small opening about thirty feet from the edge of the old road, and was surrounded by a profusion of green shrubbery that was much to the liking of the vireos. On daly two occasions did I note either of the parent birds more than forty yards away from the willow after the nest was completed, until the young had flown. I could not help but note the pretty setting for such an interesting bit of home life. The ground was carpeted with a thick growth of wild sweet pea (Lathyrus paucifioras) which was in full bloom and scenting the air with a sweet odor. One side of the openin¶ was enclosed with buckbrush (Ceanothus Sri aguitzeus) and ninehark in bloom; beyond there were several large yellow pines and Douglas fir trees; on the other side were service berry bushes, willows, and ocean spray (Schizosotus discolor) which extended to a large grove of pine and fir trees In the near distance. In and out through the surroundings were bushes of the large flowering wild rose in full hlooni, adding a touch of color to the masses of green and white.
It will be observed from the above records that the western warbling vireo differs decidedly, in its choice of a nesting site, from its eastern relative. The eastern bird builds its nest almost invariably in trees and at a very considerable height, whereas the western bird often builds in bushes or low trees and much nearer the ground. Most of the recorded nests of the western warbling vireo have been placed at not over 12 feet from the ground; and its highest nests, which seem to be exceptional, have been below the average for the eastern bird.
Eggs: The western warbling vireo lays from three to five eggs, usually four. These are quite indistinguishable from those of the eastern race. The measurements of 40 eggs in the United States National Museum average 18.4 by 13.2 millimeters; the eggs showing the four extremes measure 20.3 by 14.7, 20.1 by 15.0, and 16.8 by 12.2 millimeters.
Young: Mr. Rust (1920) found that the period of incubation was 12 days, performed by both sexes. “If my visit happened in the morning, and the male was incubating, I could almost touch the nest before he would leave. Then, alighting on a small dead fir tree nine feet from the nest, he would burst into song.” He sang at intervals on the nest. “If the female was incubating she quickly became aware of my presence, and at a distance of about five feet, would flit from the nest to a nearby bush, to begin the usual vireo scold.” Both parents assisted in feeding the young and in cleaning the nest, which was kept scrupulously clean. The male was very bold in feeding the young, so that Mr. Rust was able to take some photographs of him in the act. “I was able to observe only the male parent feeding at close range, and I was surprised to note the care he took to feed the helpless young before they were strong enough to raise their heads for food.” After the young “were several days old the male would sing from the tree as before, then fly direct to the nest and perching on the brim, would sing as if he would burst his throat.” “On one occasion,” he says, “a male Cassin Purple Finch seemed to share his joy, and, alighting on the singing tree, joined in and sang his best. The same incident occurred again when the young were a week old, but this time the male vireo seemed to resent the intrusion and drove the finch away in a hurry, chasing him some distance. * * * In securing food for the young the female gathered much larger insects than the male, often coming in with a good size caterpillar dangling from her bill. When I was near she would fly back and forth six or eight feet from the nest and scold until the food was either lost or she ate it, I never could tell which. She never fed the young whilo I was near.” When first hatched the “four naked, dark, yellow-colored young” were all “huddled up in a pile in a corner of the nest.” The young gained rapidly in size and strength, but one was found dead in the nest, when five days old. In removing the dead bird, Mr. Rust found that its claws were closed tightly over several strands of horsehair in the lining; this clutching habit seems to be characteristic of young vireos, and might prove very useful in a gale of wind. At the age of nine days the two stronger young had their eyes open, but one weakling was several days longer in acquiring its eyesight. “At the age of twelve days the young were well feathered and able to perch on the edge of the nest with a little assistance on my part. The parents became very much excited when they saw two of the nestlings out on the edge of the nest and uttered similar chirping notes trying to coax them away. On the fifth day of July they had their pictures taken for the last time; on the sixth the nest was deserted. Two days later I found the parent birds in some dense brush about seventy-five yards from the nest, but could not locate any of the young. After a severe scolding from the parents I retired and left them to their ways in peace.” Plunuzges: The plumages and their sequence are similar to those of the eastern warbling vireo, with the probability of a partial pronuptial molt about the head and breast, as noted by Ned Dearborn (1907).
Food: Prof. F. E. L. Beal (1907) made a study of the western warbling vireo in California, based on the examination of 110 stomachs, collected during the seven months from April to October, inclusive. He writes:
Insects, with a few spiders, amount to over 97 percent of the diet, leaving less than 3 percent of vegetable matter, practically all of which was taken in August and September; it consisted of wild fruit (elderberries), a few seeds of poison oak, a few other seeds, and some rubbish.
Of the animal food the largest item Is Lepidoptera; that Is, caterpillars, moths, and the like. These amount to something more than 43 percent of the whole. Caterpillars make up the great bulk of this portion of the food and are a very constant and regular article of diet. * * In April they amount to over 82 percent of the food of the month. Pupae of coddling moths were Identified In four stomachs. * * * Hemiptera are the next most important item of diet, and amount to 21 percent. They consist of stink-bugs, leaf-bugs, leaf-hoppers, spittle-insects, tree-hoppers, and scales. The last were the black olive species (Saissetia oleac). Coccinelild beetles, or ladybirds, were eaten to the extent of over 19 percent of the whole. a * * Other beetles, mostly harmful species, amount to more than 7 percent.
Hymenoptera, consisting of a few ants and an occasional wasp made up a little more than 1 percent. “A small number of flies, grasshoppers, and dragon-flies make up a little more than 3 percent of the miscellaneous insects. Spiders were eaten to somewhat less than 2 percent.”
Mrs. Wheelock (1904) says: “In the fall this bird becomes very friendly, coming into the orchards and gardens to hunt busily among the leaves for small caterpillars. At this time he is fond of the cornel berries that grow along the mountain brooks, and occasionally condescends to eat mistletoe.”
Mr. Rathbun watched a western warbling for a long time while it was busily feeding in some trees, and he says in his notes: “‘While hunting among the branches and foliage of a tree the vireo sang frequently, and at times the song was given when the bird turned its head from side to side. Often the vireo would poise in the air for an instant to take some insect from beneath a leaf, then begin again its inspection of the twigs and leaves. The bird made this distinction in anything it captured; if the prey was small, it was eaten as soon as taken; but if of large size, it was well minced before being swallowed.”
Voice: All the habits, except as mentioned above, and the song of the western warbling vireo do not seem to differ from those of its eastern relative. It is an equally persistent singer. Mr. Ilathbun says in his notes: “Its warbling song is heard incessantly from the time of its arrival until nearly the middle of June, then much less frequently. I have noticed that in the early part of the season the character of the weather has no effect whatever on its tendency to sing, but it does appear to influence the bird later, for then during the cool and lowery days its song is shorter and longer intervals elapse between the renditions. And should a day come that is stormy, then the bird may not be heard at all. During the flood period of its song the singer is seemingly carried away by his efforts, often singing continuously for many seconds, renditions of his song flowing along like the current of a stream. Its song practically ceases by July, and in this month is heard more often in the morning hours. It seems to cease singing sometime in early August, but we have heard it warble a little in September during the time it is moving south.”