Contributed by Winsor Marrett Tyler
[Published in 1950: Smithsonian Institution United States National Museum Bulletin 197: 335-348]
Spring.--The trees are leafing out fast when the red-eyed vireo arrives in New England from its tropical winter home. Many of the spring migrants are already here before him, and his song may pass unnoticed at first, except by an experienced ear, among the chorus of their voices. Only a practiced eye, too, will catch sight of him where, high over our heads, he is singing--a little green bird surrounded by the green leaves of the elms and maples. When we do find him, we see that he is well out on the smaller drooping branches, constantly moving about among the leaves, hopping along the twigs, or taking short, quick flights to other branches. He is feeding, picking up insects from the leaves all about him, singing as he goes, in short, hurried phrases that do not interrupt his continual search for food. Hour after hour, day after day, he sings from our woodlands, from the trees on the shore of our streams, and from the tall elms along the streets of our towns and villages--like a happy laborer, whistling at his work.
Courtship.--Aretas A. Saunders (1938) writes: "The males sing vigorously between nestings, and on one occasion I observed courtship and a courtship song at this time. The date was July 28, 1933, and the male sang its song in a soft whisper, audible only a short distance. During the singing his wings trembled, and he moved about in front of his intended mate, who sat silently watching and finally flew away, with him in pursuit."
Years ago, late in May 1909, I saw a bit of courtship behavior between a pair of red-eyed vireos. The birds were near at hand, in plain view, not far above my head. My attention was drawn to them by hearing some unfamiliar notes, high-pitched and rather squeaky in tone, but uttered very quietly, made up of fine little trills and some long-drawn-out, faint whistles, not suggesting a vireo at all. At the time I described their actions thus (Tyler, 1912):
The two birds were very near each other; so near that their bills might have touched, although they did not. The male, or at least the bird who played the active role, faced the side of the other bird, so that their bodies were at right angles. . . . He rocked his body, especially his head, from side to side, his bill sweeping over the upper parts of the other bird, never touching her, nor, indeed, coming very near it, for his head was above and a little to one side of her back. In swinging from side to side, he moved slowly, but with a tenseness suggesting strong emotion. In contrast to the fluffy female, the feathers of the male were drawn closely about him, so that he looked slim and sleek. The neck seemed constricted, giving him a strangled appearance.
Three years later, again in May, I caught another glimpse of vireo courtship. A male, with feathers puffed out, perched in a low shrub, was singing in characteristic phrases, but without tone quality, the notes given softly in a whispered voice. He flew toward the other bird, and they darted away together.
Nesting.--The red-eyed vireo builds a dainty little pensile nest suspended usually from a forking, horizontal branch of a shrub, or low branch of a tree, rather below the level of our eyes as we walk through second-growth. The nest is a beautifully finished piece of workmanship, constructed of fine grasses and rootlets, bits of birch bark, and paper from wasps' nests, bound together and to the supporting branches with spider's or caterpillar's webbing, and, perhaps the most constant material, long, narrow, flexible strands of grapevine bark, which help to hold up the cup of the nest. It may be ornamented on the outside with bits of lichen. Dr. Arthur A. Allen (1932) says that it has thinner walls usually than other vireo's nests.
F. N. Whitman (1924) found a nest only 2 feet from the ground, and Charles R. Stockard (1905) speaks of one "situated sixty feet from the ground in the topmost boughs of a gum tree." Five to ten feet elevation is the usual height.
Minna Anthony Common (1934) gives this interesting account of the building of a nest:
July 6, 1933, Found: two pieces of tangled ravellings hanging from fork on a beech branch four feet from the ground. It appears like the starting of a nest. . . .
July 8: We have decided it is a nest, for there are a few more ravellings hanging down a foot or so.
July 9, 1933, Late afternoon: We saw both Red-eyed Vireos (Vireo olivaceus) working at the nest. The bunches of untidy ravelling hang lower, but there is no bottom to the nest. Birds are absolutely silent.
July 10: Some loose network may be seen forming a bottom to the nest. Several bits of birch bark have been skillfully intertwined on the outside. Both birds work. The ravellings are mostly caught up.
July 11, 6 a.m.: Saw one bird pull a small, short strand of bark from a dead oak twig. He carried it to the nest and was back for another in four minutes. . . . At the end of the day the nest appeared finished. All loose ravellings had been caught up and fastened. A piece of paper 3/4 by 1 1/2 inches in size is spread across the floor of the nest inside.
Francis Hobard Herrick (1935) describes in detail the construction of a red-eyed vireo's nest which he watched from a distance of 10 feet. The following is a condensed account of his report:
With a vireo or an oriole and all such as build similarly suspended nests, the work of construction must needs begin with securing the first fibers to two or more twigs destined to support the future nest. Upon these primary strands is built up a loose, free-hanging fibrous mass, the primary nest mass, and this is gradually extended downward while, pari passu, the attachment is carried outward along each of the divergent twigs. A rim and bottom are gradually produced in a way to be presently described, and the gap or open side, opposite the first-formed hanging mass, long remains open; with the vireo, as with the oriole, it is filled in last. . . .
The most striking actions of this vireo that I noticed on the first day were as follows: (1) winding silk and fine threads of bast over the forks of the twig at about an inch from their junction; (2) building downward from this support a loose mass of fibers--corresponding to the primary nest mass of the oriole's work--perfectly secured but giving no hint of the beautiful cup-shaped structure that was to appear; (3) carrying the suspension forward and downward until one could recognize part of the concave wall of the future nest, or hardly more than the half of a vertically divided cup; (4) finally, attempting to rest in the imperfect nest and use the breast for molding long before it was physically possible to make such movements effective. . . .
At four o'clock on the second day the frame of this nest was evidently completed. It was composed almost wholly of fine bast, bark strippings, and spider's silk, the latter having been derived from the egg-cocoons of such species as nest on the under side of leaves or against the clapboards of houses. . . .
In reality the work of construction lasted nearly five days, but from the close of the third day until the end of the fifth, active labor gradually slowed down; the hen would sit in her nest-cup for longer and longer intervals, until June 4, or the sixth day from the start, when she remained to lay her first egg, which was deposited after 7:30 o'clock in the morning.
W. J. Ericksen (1919) says of nest building: "A peculiarity of this species which I have noted both in Liberty County [Georgia] and elsewhere is a habit the birds have of destroying partially completed nests built by them. I once watched a pair remove piece by piece the material from a nearly completed nest, and weave it into another which they had begun a few yards distant."
Ora Willis Knight (1908) gives the measurements of a nest as "two and a half inches deep outside by one and a half inside, the external diameter was three and the diameter inside two inches."
Eggs.--[AUTHOR'S NOTE: Four eggs generally make up the set for the red-eyed vireo, but sometimes only three are laid and very rarely five may be found. These are mostly ovate, rarely slightly elongated. They are pure lusterless white, and are usually sparingly marked, chiefly toward the larger end, with fine dots or small spots of reddish brown, or darker browns, or blackish; rarely an egg is nearly or quite immaculate; an occasional set may contain eggs that show large spots or small blotches of light browns, but such cases are rare.
The measurements of 50 eggs in the United States National Museum average 20.3 by 14.5 millimeters; the eggs showing the four extremes measure 22.9 by 15.8, 21.8 by 16.3, and 18.3 by 13.2 millimeters.]
Young.--Ora W. Knight (1908) gives the incubation period as 12 to 14 days. M. G. Vaiden, of Rosedale, Miss., writing to Mr. Bent of nests he had studied carefully, found that the eggs hatched in 11 days. He began his count the day after the last egg was laid; in one case it took an extra day.
Samuel A. Harper noticed so much irregularity in the incubation of the female in three nests under his observation that none of the eggs hatched.
Aretas A. Saunders (1938) states that "both sexes share in incubation and feeding young" and Forbush (1929) says: "Occasionally a pair may raise two broods in a season."
Francis H. Herrick (1904) remarks: "When the young Vireos were a week old I began to watch their nesting habits at night more closely, and found that, while the male apparently roosted near by, the female invariably slept on the nest. At from fifteen to twenty minutes after sundown she was regularly at her post, and even at this hour usually fast asleep. So profound, indeed, were her slumbers, that I could often enclose her in my hand and stroke her feathers without awaking her. She slept with her head twisted back and buried deep in the feathers between the shoulders. An apparently headless trunk or a little ball of feathers was all that could be seen, and the only motion discernible came from the regular pulsations of breathing." William Brewster (1936) recounts a somewhat similar experience.
T. C. Stephens (1917), from a close study of a nest, found that "75% of the work of feeding was done by the female, while the male did about 25%."
Francis H. Herrick (1904) reports that "the eyes began to open on the fourth day, when the first faint cheeps of the young were audible at a distance of a few feet," and, according to Burns (1921), the young birds leave the nest 12 days after hatching.
Young redeyes are very importunate; even when they have reached full size they fly to their parents, begging for food, using a rather long, sustained note that sounds like theet and is strangely like the food call of the black-capped chickadee.
My notes taken in the White Mountains, N. H., some years ago, state: "I was surprised to find parents still feeding their young. On September 8th, one or two young birds (fully grown, of course) followed an adult about, insisting on being fed. The old bird had a green worm in its bill, and one of the young birds, darting toward it, snatched it away from the parent, who tried to escape it seemed. Apparently the family ties were holding by a thread, and the old bird was doing its best to sever them."
Forbush (1929) reports a case of a bird feeding young, on September 15, barely able to fly.
Plumages.--[AUTHOR'S NOTE: Dr. Dwight (1900) calls the natal down of the red-eyed vireo "pale drab-gray" and describes the juvenal plumage as "above, including lesser wing coverts, drab. Wings and tail olive-brown, edged with bright olive-green, brightest on the secondaries and tertiaries. Below, silky white, faintly tinged on the sides and crissum with primrose-yellow. Superciliary stripe dull white; lores and postocular streak dusky. Iris walnut-brown."
The first winter plumage is acquired by a partial postjuvenal molt in August and September "which involves the body plumage, the wing coverts (often the tertiaries) but not the rest of the wings nor the tail. . . . In plumage young and old are practically indistinguishable in the autumn, but the iris of young birds is brown while they remain with us. . . . The iris becomes dull red before the birds return in the spring."
The nuptial plumage is apparently acquired by wear, with very little fading apparent. A complete postnuptial molt for birds of all ages occurs in August and September.]
About six-sevenths of the total food of the Red-eye is composed of animal matter, almost exclusively insects, and one-seventh is vegetable. The latter is made up almost entirely of wild fruits which are eaten chiefly in the months from August to October. The favorite kinds are blackberreis, elderberries, and fruits of spicebush, dogwood, Virginia creeper, and sassafras.
A third of the total food of this vireo is composed of caterpillars and moths, mainly the former. Tent caterpillars, a beech caterpillar (Fentonia marthesia), the hackberry caterpillar (Chorippe celtis), and various oak caterpillars (Acronycta afflicta, Apatela, Notodonta, and Anisota) are among the injurious forms devoured. Mr. Forbush reports the Red-eye to be one of the most effective enemies of the gipsy and browntail moths *** and Dr. Tothill credits the species with destroying in various years, from 11.4 to 89.5 per cent of the broods of fall web worms in Nova Scotia***.
Beetles, hymenoptera, bugs, and flies rank next to lepidoptera in importance as food items of the Red-eye. The beetles include a considerable number of forms injurious to trees.
Then follows a list of 43 species. He continues:
Other insects, more or less prejudicial to the welfare of the forest which the Red-eyed Vireo includes in its bill-of-fare are the walking-sticks, cicadas, spittle insects, tree hoppers, leaf hoppers, scale insects, sawflies, and carpenter and other ants.
While we are reciting the good record of this bird we may as well add the names of a few agricultural pests: the striped and spotted cucumber beetles (Diabrotica vittata and D. 12-punctata), the click beetles (adults of wireworms), the clover-root weevil (Sitona hispidula), the clover leaf weevil (Hypera punctata), and the plum curculio (Conotracheius nenuphar).
The only harm done by the Red-eye is the destruction of certain useful parasitic and predatory insects, but in view of the splendid record of the bird in feeding on injurious forms, this may well be overlooked. We may be sure that in its industrious scanning of our woodland trees, the Red-eyed Vireo is ever on the alert to snap up the insects infesting them, by far the most of which are not there for the good of the trees.
To this long list T. C. Stephens (1917) adds other items. He says:
One of the most interesting facts obtained in the study of these Vireos was that land snails formed a considerable portion of the nesting diet. In the food table (Table II) it is shown that the snails stand fifth in numerical abundance. . . .
Some of the snails were specifically identified. Thus twelve snails were recognized as Succinea avara, and all of them delivered by the female. At visit No. 210 the male carried one specimen of Bifidaria armifera. . . .
At visit No. 264 the female bird brought a spider to the nest which was of a species that I had noticed frequently in the beaks of the parent birds, as well as often in the woods. I was able to take this specimen from the beak of the parent bird and preserve it for later identification. In due time this specimen was identified by Mr. J. H. Emerton as Epeira trivittata Keyserling. This is a very common round web spider, whose web is stretched between the branches of the trees at all heights up to fifteen or twenty feet, and would thus be readily found by the foliage gleaning Vireos.
Arthur T. Wayne (1906) makes an interesting observation on the food of the redeye in the Southern States in autumn. He writes:
The controlling influence upon the migration of this bird in the autumn is the presence or absence of the seeds (fruit) of the magnolia (Magnolia grandiflora). The fruit of this beautiful tree begins to ripen during the first week of September, but the greater part ripens through October, and many seeds remain in the cones until November. The color is coral-red, and some specimens are about three-fourths of an inch in length, but the great majority average about half an inch. These seeds contain a large amount of oil, and when this vireo has been feeding upon them for any length of time it becomes very obese. There are many beautiful trees on this plantation, and I have often sat on the steps of the old Colonial house and watched these birds while feeding upon the fruit. The tree that has the most fruit attracts nearly all the vireos in a radius of perhaps a quarter of a mile, and I have often counted as many as fifty vireos in one tree. As long as the fruit is to be had, the vireos remain, but as soon as the supply becomes scarce or exhausted, the vireos depart.
Paul Wanamaker, Dean Forest, and Charles L. Bull (1931) report on the food which they fed to an injured young vireo. They say: "In five minutes he was taking blue-bottle flies from our finger-tips, having refused our earlier attempts to feed him bits of earth-worms. A daddy-long-legs was snapped up with great gusto, as were moths, a dragon-fly, a small inch-worm, etc. . . . His entire menu for the first day consisted of: 40 blue-bottle flies; 30 elderberries; 25 grasshoppers, a tentful of tent caterpillars, of which he ate at least 15; 5 moths; 2 daddy-long-legs; 1 dragon-fly, 1 young locust; 1 inch-worm; 1 spider; 1 bee; 1 butterfly--a total of 123 distinct items."
Behavior.--Dayton Stoner (1932) writes thus of the favorite habitat of the red-eyed vireo: "Woodland with an undergrowth of slender saplings from six to ten feet high seems to appeal to this bird most."
Such a situation affords the vireo with a nesting site not far above the ground in the low shrubs and a source of food in the high canopy of the overhanging branches. These requirements, however, are often closely approximated in settled communities, so that the redeye, although a forest-loving bird, nevertheless finds congenial surroundings for summer residence in the orchards, gardens, and tree-bordered streets of built-up sections of the country. It sometimes spends the summer months even in the parks of our large cities with blocks of houses on all sides, such as, rarely, the Public Gardens in Boston, Mass.; but in the main the red-eyed vireo is a woodland bird.
Perley M. Silloway (1923) describes thus the vireo's habitat in the western Adirondack forest: "The Red-eyed Vireo abounds in almost all aspects of the forest except dense bog woods. It lives in clearings where small trees have obtained a standing, in the borders of the Burn, and in open woodlands of every kind. It is one of the birds whose preferences for timber lead them into the virgin forest, but there they require a 'margin' of some sort, usually a brook or a bog, which breaks the forest canopy in some degree. Though it nests most commonly in sapling growth it hunts and sings in trees, preferably such as form spreading tops at medium height, but it has little to do with evergreens."
A. A. Saunders (1942), writing of the bird in the woodlands of New York State, reports that it is "common in Oak-Hickory, Maple-Beech, Cherry-Aspen, and river valley forests. In the higher Maple-Beech, where hemlock is missing and few birds occur, it is still a common bird. It is also common in mature forests." Saunders also states (1938):
Red-eyed vireos live so much of the time in the trees, hidden among thick foliage, that they are not frequently observed. If it were not for the song, their presence, in spite of their numbers, would be difficult to detect. . . . I have distinguished individuals mainly by the location of their singing trees. This is fairly definite, a particular bird being found in the same tree day after day. Occasionally it leaves the tree and sings elsewhere, but it does not wander from place to place as the blue-head does.
This would seem to be evidence that the red-eyed vireo has definite territory, but I have never observed fighting or jealousy over such territory.
Francis Zirrer, of Hayward, Wis., writes to Mr. Bent of a case of belligerency in the redeye. He says: "During the nesting season some are quite pugnacious. They will attack almost any bird that ventures too close to a nesting tree. The little bird will drop like a stone almost at the head of the culprit. During the nesting season of the pileated woodpecker, when the big birds fly low and silently, like phantoms between the tree trunks and decaying stumps, I have seen this vireo strike the big bird with such force that it nearly lost its balance, looked and acted surprised--and flew away."
The red-eyed vireo is not commonly so tame while on the nest as the solitary, but Ernest Harold Baynes (1922) tells the following astonishing story of his "friendship" with a female redeye:
I knew that vireos have a reputation of being willing to meet one half way in the matter of making friends, so I decided to make an advance. First I went to a dry and sandy spot where I turned over large stones until I found some ants' eggs. Then I selected a dead weed stalk about five feet long and impaled an ant's egg on the sharp end of it. With this I very quietly approached the nest and held out my offering at arm's length, until the white morsel was within reach of the vireo. At first she looked alarmed, then astonished, and a moment later rather bored, for she turned her head away and refused to look at the proffered food. But I waited patiently, holding the tip of the weed stalk within easy reach. At last she turned her head as if the temptation to do so could no longer be resisted. She now showed keen interest in the proceedings, took a sharp look at the white delicacy at the end of the stalk and then as much as to say "Hello; that is an ant's egg, isn't it?" stretched out her neck and took it. . . .
A moment later she confirmed her own opinion by taking another ant's egg in the same way, after which I quietly withdrew, leaving her to digest both her food and her strange experience.
Next day I returned and after she had promptly accepted a few more ants' eggs from the end of the weed-stalk, I stepped up a little closer and offered one between my thumb and forefinger. After a little hesitation she took it, and from that moment we were on friendship's footing. She seemed much interested, if not actually pleased, whenever I approached; she would sometimes stretch far out over the rim of the nest in order to make quick connections with the food I brought her, and did not mind in the least if I stroked her on the head or back with my finger. At first she was a little nervous when I stroked her throat, and when I persisted she slipped off the nest. But as she got used to me she minded less and less and would even allow me to lift her off her eggs and put her gently back. . . .
Many people were introduced. . .and children especially experienced ecstatic joy at the privilege of feeding and stroking a wild bird in her own home.
Several times in the course of the past 30 years or so, I have seen a red-eyed vireo acting in a very odd manner. It has occurred when an adult is feeding a full-grown young. The old bird suddenly departs, for a moment, from its normal behavior; it draws its feathers tight to its body and sways slowly from side to side through a wide arc, certainly as great as 90 o. If the two birds are facing each other, as they usually are, the bill of the adult points successively far to each side of the young bird, over and over. The old bird gives the impression of being in a sort of trance, or as if it were trying to influence the other bird in some strange way, although the action probably has a more prosaic explanation. Behavior of a similar nature is described under "Courtship." I have never seen any other species of vireo act in this manner.
Arthur B. Williams (1940) describes a very unusual observation:
On July 16, 1934, the writer, while engaged in making a survey of the bird population of a tract of beech and sugar-maple forest near Cleveland, Ohio, noticed a Red-eyed Vireo (Vireo olivaceus) plunging into a shallow pool of water at the edge of a woodland brook. This unusual behavior was repeated several times. The bird would work down a small branch overhanging the pool until it was about eight inches above the water. Here attention was fixed at a certain spot in the water below, and shortly the bird would dive in head first as a kingfisher does. It would then fly to a perch in a tree about twenty-five feet away and eat something apparently captured from the water. Once the bird was nearly submerged and had to stop to shake the water off its plumage before eating the morsel.
Voice.--The red-eyed vireo is preeminently famous as a singer. No other of our birds sings so persistently all day long, and because his long-continued series of utterances, given in short, emphatic phrases, going on for hours, calls to mind a lengthy sermon, he has won the title "Preacher." Of this epithet Bradford Torrey (1889), with sly humor, expresses this opinion: "The red-eye's eloquence was never very persuasive to my ear. Its short sentences, its tiresome upward inflections, its everlasting repetitiousness, and its sharp, querulous tone long since became to me an old story; and I have always thought that whoever dubbed this vireo the 'preacher' could have had no very exalted opinion of the clergy."
Nevertheless the preacher sings a cheerful song, and when we study it we find it has its good points as well as its shortcomings. It is tiresome chiefly because most of the phrases end with a rising inflection, giving the impression of a long series of interrogations, the voice seldom coming to rest as before a period. Wilson Flagg (1890) brings out this point very well when he says: "We might suppose him to be repeating moderately, with a pause between each sentence, 'You see it,--you know it,--do you hear me?--do you believe it?' All these strains are delivered with a rising inflection at the close, and with a pause, as if waiting for an answer."
Some characteristic phrases, which I have jotted down while listening to a singing bird, may be written, cherry-o-wit, cheree, sissy-a-wit, tee-oo, and many others. At times during the day, and invariably at early dawn, when the bird is not feeding, it sings with almost perfect regularity, the phrases following each other at a rate of from 60 to 80 per minute, and rarely a bird will sing for a considerable period with little variation in his phrases.
There is commonly much variety in the song. A. A. Saunders says that the number of different phrases used by an individual bird may be as many as 40, although about 25 is a more usual repertoire. "The pitch of the song," he says, "varies from D' ' ' ' to E flat ' ' ', half a tone less than an octave. The quality is clear, but rather colorless, as compared to the other species of vireos. The phrases are composed of two to five notes each, five-note phrases being rather rare. The notes of the phrases are generally joined abruptly and only rarely slurred together. This gives the song a choppy effect, and with the colorless quality gives the effect of talking rather than singing--talking in short, quick, exclamatory or interrogatory sentences."
Several observers have noticed that the bird occasionally introduces a phrase resembling a note of the crested flycatcher, and Francis H. Allen says: "I have heard it imitate the olive-sided flycatcher and the bluebird."
William Brewster (1938), writing of birds at Lake Umbagog, Maine, says: "The males sing regularly until late August, and on September 26, 1899, one sang feebly and brokenly," and A. C. Bent says in his notes that he heard a bird singing daily from August 31 to September 14, 1900, in Massachusetts.
Albert R. Brand (1938) gives the approximate mean vibration frequency of the song as 3,600, rather higher than that of the white-eyed and yellow-throated vireos.
The common complaint note may be written queee, a discontented, petulant call, inflected downward, about as long as the catbird's snarl.
Field marks.--If an observer is near enough to a redeye to see the vireo bill, the gray crown, bordered by black lines, the black line through the eye, the white under parts, and the unmarked wing, it is an easy bird to identify. The red iris, seen only at very short range, is not a reliable field mark.
The red-eyed vireo in plumage is remarkably like a Tennessee warbler, but the needlelike bill of the warbler and its paler side of the head distinguish the two birds.
Enemies.--In addition to the danger of capture by small hawks, the red-eyed vireo is subject to attack by the red squirrel, and the chipmunk, as the two following quotations show, respectively. Wiliam Brewster (1936) relates this observation made at Concord, Mass., on June 10, 1906:
Again this afternoon Gilbert heard the Vireos crying anxiously. Looking out through the screen door, he saw the Squirrel on the branch within a few inches of the nest, eating something. Presently he dropped a portion of the shell of one of the Vireo's eggs. He then wiped his face with his fore-paws and wiped the latter on the branch. The next minutes he bent forward until his head and fore shoulders disappeared in the nest and almost immediately reappeared on the branch with another egg in his mouth. The Vireos assailed him frantically and one of them struck him with her bill when he was in the nest. Probably because of their attacks, he almost immediately took the second egg off with him, running up the main trunk of the tree until lost to sight in the foliage of its crown.
A. A. Wood (1920) records a similar experience, saying: "Last spring (June 8, 1918) I noticed a Red-eye excited over something, then saw a chipmunk climbing the sapling the bird was in. When he was about eight feet up, the vireo darted down knocking him to the ground. The other bird was on the nest at the end of one of the branches."
In reference to the cowbird's relation to the red-eyed vireo, Herbert Friedmann (1929) says: "This bird is so frequently imposed upon that it is difficult to think of the Cowbird getting along without the pensile, cup-like nests of the Red-eye. No species suffers more and few as much. . . . Occasionally this Vireo covers over, or buries (under a new nest floor), the parasitic eggs as does the Yellow Warbler, but on the other hand it has been known to incubate Cowbirds' eggs even when none of its own were present, and almost always seems not to mind the strange eggs in the least. Three and four of the parasitic eggs are sometimes found in a single nest."
Harold S. Peters (1936) reports the finding of two species of lice and three species of mites in the plumage of this vireo.
Fall.--After its long period of song is over the red-eyed vireo becomes comparatively inconspicuous. In the autumn migration it is not a prominent bird. We meet an individual or two, associated with many of the flocks of warblers as they pass through in September, but perhaps more often we come upon a single bird low down in shrubbery where it is feeding on berries, notably those of the wild and cultivated cornels. Here, in marked contrast to its behavior earlier in the season, it moves about slowly, generally in complete silence, although it may sometimes give a peevish snarl.
It seems strange to see a redeye in this subdued mood, for all through the summer we have associated the bird with constant activity, quickness, and an almost endless stream of loud, exuberant music. Even at this late date, however, the bird is on the watch for insects and continues to examine in its characteristic, careful manner the twigs and what leaves remain on the branches, twisting its neck to peer under the leaves with a sidelong glance.
When it flies it progresses with an easy grace, more rapidly than the warblers and chickadees which are flitting through the treetops at this season, and it surpasses its companions in its precise coordination of movement.
Taverner and Swales (1908), in their study of the fall migration at Point Pelee, report that red-eyed vireos are regular migrants from late in August to late in September, some remaining "well into October," but not many birds are seen on a single day, except on rare occasions.
Alexander F. Skutch writes to Mr. Bent of the migration through Central America thus:
"The red-eyed vireo is known in Central America only as a
transient, journeying between its winter home in South America and
its breeding range in North America. Its migration route, north of
the Isthmus of Panama, appears to center in the highlands--where,
however, it is seldom recorded as high as 6,000 feet--but extends
down the Caribbean slope to sea level and on the Pacific slope to
at least 1,500 feet. September is the month when these vireos pass
southward in greatest numbers; but stragglers have been recorded
in Costa Rica as late as October 28 (Carriker) and November 10 (Skutch).
The northward passage begins late in March and is at its height in
April, while an occasional straggler may be seen early in May. As
they pass through Central America the red-eyed vireos are met
singly or in small flocks. I have not heard them sing while
Red-eyed Vireo* Vireo olivaceus
*Original Source: Bent, Arthur Cleveland. 1950. Smithsonian Institution United States National Museum Bulletin 197: 335-348. United States Government Printing Office