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Philadelphia Vireo

Known for their pale yellow plumage, these birds are more common in Canadian forests than in Philadelphia.

The Philadelphia Vireo is a nocturnal migrant, stopping during the day to forage, often in a small group. It prefers willow groves and early successional habitats. The size of the Philadelphia Vireo’s breeding territories varies depending on the available food supply and the density of the population in that area.

Vireos as a group are a frequent host to the Brown-headed Cowbird, which lays its eggs in the nests of other birds. The Philadelphia Vireo is no exception, and increasing fragmentation of forests may provide cowbirds with more opportunities to parasitize this species.


Description of the Philadelphia Vireo


The Philadelphia Vireo is grayish-green above, pale yellow below, and has a gray crown, a dark line through the eye, and a white supercilium.

Philadelphia Vireo

Photograph © Greg Lavaty


The sexes are similar.

Seasonal change in appearance



Juveniles are similar to adults.


Philadelphia Vireos inhabit second growth deciduous and mixed woodlands.


Philadelphia Vireos eat insects and some fruits.


Philadelphia Vireos forage actively in trees and shrubs, and occasionally hover to capture prey.


Philadelphia Vireos breed across much of southern Canada. They can be seen across the eastern half of the U.S. during migration, and they winter in Central America. The population appears to be stable.

Fun Facts

The Philadelphia Vireo breeds farther north than other vireos, and is only an uncommon migrant in its namesake city.

Philadelphia Vireos are often overlooked because Red-eyed Vireos are usually much more numerous.


Calls include a nasal wheeze, while the song consists of a slow, weak warble.


Similar Species

  • The Warbling Vireo has a paler crown and lacks the bold dark line through the eye.


The Philadelphia Vireo’s nest is a cup of bark strips, weeds, and lichens, is lined with soft materials, and is placed on a forked twig of a tree.

Number: Usually lay 4 eggs.
Color: White with darker markings.

Incubation and fledging:
The young hatch at about 14 days, and begin to fly in about another 2 weeks, though continuing to associate with the adults for some time.


Bent Life History of the Philadelphia 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 Philadelphia Vireo – the common name and sub-species reflect the nomenclature in use at the time the description was written.



This vireo was described and named by John Cassin (1851) from a specimen collected in September 1842 in some woods near Philadelphia. For a number of years thereafter very little was known about it, though Thure Kumlien wrote to Dr. Brewer (Baird, Brewer, and Ridgway, 1874) that he had been familiar with the bird in Dane County, Wis., since 1849, and had “collected it every year since that period, finding it both in the spring and fall.”

William Brewster (1880) was the first to give us any considerable account of the distribution and habits of the Philadelphia vireo, with special reference to its occurrence in New England, as observed by him and others, between 1863 and 1876, including his own introduction to the species at Lake Umbagog in 1872. He says of its haunts there:

Although In the breeding season the species * * * seems to be generally distributed throughout the wooded region about Umbagog, it occurs less commonly in the heavily timbered portions. As upon its first arrival, it chiefly affects the younger growths which have sprung up in the clearings and over old burnt lands. Its favorite haunts are the coppices of wild-cherry and gray birches by roadsides; rocky knolls tufted with black and yellow birches; the various small trees and tall shrubs that fringe the wood-edges; and deserted farms, where cool groves of vigorous young paper-birches and glaucous-foliaged poplars are grouped over the neglected acres, with Intervals of sunny openings between. Bat wherever found, like most of the members of the Vireosylvia group, It makes Its home In the tops and upper branches of the trees, rather than In the thickets beneath.

Then, 17 years later, came Dr. Jonathan Dwight’s (1897) full and interesting account of the Philadelphia vireo, as he had observed it near Tadousac, Quebec, on the Saguenay River. He was struck with the close resemblance between the red-eyed vireo and the Philadelphia, saying: “Both frequent the same localities in the wilderness, but the Philadelphias rather shun civilization and rarely appear, like the Red-eyes, in the village trees. Both prefer to sing in the upper branches, but I have seldom found the Philadeiphias in the rambling groves of birches which are the especial delight of the Red-eyes, and they are more partial to the low, bushy, second growth or copses of alders sprinkled with stray trees.”

The Philadelphia virpo is now known to breed in the Canadian Zone in southern Canada, from Alberta to New Brunswick, and in the Northern States, from North Dakota to Maine, in all suitable wilderness localities. L. M. Terrill writes to me: “The Philadelphia vireo is common and well distributed in suitable localities wherever I have been in Gasp4, especially in the extensive alder growths in bottomlands and along streams. I also found it among dense patches of mountain maple (Acer spicatum) and alders well up on mountain slopes, but it was not as common here as along streams.”

Spring: From its winter home in Central America this vireo migrates northward in spring over most of the United States, at least from the Mississippi Valley eastward. It does not seem to be abun. dant anywhere, and generally not even common. It is, however, easily overlooked, as it sings very little on migration and often frequents the tree tops, where it moves about in a very leisurely manner and where its colors blend well with the fresh foliage; for these reasons, it may be commoner than is generally supposed. It passes through the States in May, coming along with waves of the later migrating warblers. It is generally seen at this season in the small trees, thickets, and shrubbery bordering streams or marshes, but sometimes in the tree tops of the more open woodlands or in scattered trees.

Among the many attractive bits of nature writing from the pen of that gifted writer, Mr. Brexvster’s (1880) account of this vireo at Umbagog Lake, Maine, is one of his best:

The Philadelphia Vireos usually arrive at Umbagog during the last week of May, or, if the season be a late one, in early June. They come with the last flight of Warhiers, when the forest trees are putting on a drapery of tender green, and the moose-wood is white with snowy blossoms. They are most apt to he found singly at this season, though they not infrequently associate with the various species of Wnrblers. For some time after their first appearance they are severely silent, and, although by no means shy or suspicious, their habits are so retiring and unobtrusive, that their presence may be easily overlooked. Their motions are essentially like those of all the rest of the genus. A branch shakes, and you catch a glimpse of a pale lemon breast that matches well with the tint of the thin foliage. Then the whole bird appears, hopping slowly out along the limb, and deliberately peering on every side in that nearsighted way peculiar to the tribe. Occasionally its search among the unfolding leaves in rewarded by the discovery of some luckless measuring-worm, which Is swallowed with the same indifference that marks all the bird’s movements. You begin to feel that nothing can disturb the equanimity of the little philosopher, wben it suddenly launches out into the sunshine, and, with an adroit turn, captures a flying insect invisible to human eyes. The next moment there is a dim impression of glancing wings among the trees, and it has vanished. There Is little chance of finding it again, for its voice has as yet no place in the chorus that rises from the budding thickets around.

Nesting: Evidently Ernest T. Seton (1891) was the first to report the discovery of the nest of the Philadelphia vireo, which he found on the west slope of Duck Mountain in Manitoba; his report follows: “On June 9, 1884, near Fort Pelly, on the upper Assiniboine I found a Vireo nesting in a small bluff of poplar and willow. The chosen site was in the twigs of a willow some 10 feet from the ground; the nest was the usual suspended cup formed of fine grass and strips of birch bark. * * * On June 13, the Virco began to sit on her four eggs. I shot her and found her to correspond exactly with Cones’ description of pltiladelpkicus, except that the yellow on the breast was quite bright. The eggs closely resembled those of the Red-eyed Vireo, but were destroyed by an unfortunate accident before they were accurately measured.”

Although Mr. Brewster (1903) had been more or less familiar with this virco in the Lake Umbagog region since 1872, it was not until June 14, 1903, that he succeeded in finding its nest. He describes the incident in his inimitable way and gives one of the best descriptions of the nest and its location that I hav&seen. He had been listening to the song of a vireo, which he suspected might be a Philadelphia; it was concealed in the top of an aspen (Populus tremuloides), and he was gathering stones to throw into the tree to make it move, when it occurred to him that some vireos sing on their nests. He writes:

This reflection caused me to drop the stones and begin looking for a nest Instead of a bird. A few moments later I saw, through an opening In the foliage, in the very middle of the tree, scarce ten feet below Its topmost twigs and fully thirty feet from the ground, a globular object of a light grayish brown color. Holding my glass on it with some difficulty: for I was now actually trembling with excitement: I made it out clearly to be a small, neatly-finished and perfectly new-looking Vireo’s nest attached to a short lateral twig of one of the long, upright terminal shoots that formed the crown of the aspen. Looking still more closely I could see the head of the sitting bird and even trace the swelling of his throat and the slight opening of his bill as he uttered his disconnected notes. Soon after this he left the nest and flying to a neighboring tree alighted on a dead twig where I had a clear view of him and quickly satisfied myself that without question he was a Philadelphia Vireo.

The next morning the nest was taken, with the three fresh eggs that it contained; dissection of the female showed that no more eggs would have been laid. Brewster continues:

The nest was hung, after the usual Vireo fashion, in a fork between two diverging, horizontal twigs. One of these, a lateral branch from the upright shoot already mentioned, is rather more than a quarter of an inch in diameter and evidently formed the chief support, as the other twig is scarce thicker than the flower stem of a buttercup. The nest is firmly bound to both for some distance along its rim. It is much longer than broad, measuring externally 3.20 inches In length, 2.75 in width, and 2.65 in depth; internally 2.00 in length, 1.50 in width, and 1.35 in depth. Its walls are more than half an inch thick In places, its bottom almost a full inch. It appears to be chiefly composed of interwoven or closely compacted shreds of grayish or light brown bark, apparently from various species of deciduous trees and shrubs as well as, perhaps, from dried weed stalks. The exterior is beautifully decorated with strips of the thin outer bark of the paper birch, intermingled with a few cottony seed tufts of some native willow still bearing the dehiscent capsules. Most of these materials are firmly held in place by a gossamer-like overwrapping of gray-green shreds of Usa cc, but here and there a tuft of willow down or a piece of curled or twisted snow-white bark was left free to flutter in every passing breeze. It would be difficult to imagine anything in the way of external covering for a bird’s nest more artistically appropriate and effective. The interior, too, Is admirably neat and pretty, for it is lined with the dry, tan-colored needles of the white pine (among which are a very few slender blades of grass), arranged circularly in deep layers around the sides and bottom of the cup in which the eggs were laid.

Philipp and Bowdish (1917) found three nests of the Philadelphia vireo in northern New Brunswick in 1916. “The situations where nests were found, as well as where additional birds were observed, were, in every instance, on islands or along the shores of river bottoms, with a growth of willow and alder.

“The nests found were in slender forks of alder, at a height varying from ten to seventeen and one half feet (the latter actual measurement). On June 17, two of these nests held four eggs each, the third five.” Their description of the nests is not very different from Mr. Brewster’s.

Dr. Harrison F. Lewis (1921) was fortunate enough to have a pair of Philadelphia vireos build their nest in a young rock maple, within 30 feet of the front door of his residence, in the suburbs of the city of Quebec. He made the best of this unusual opportunity by watching the birds and their nesting activities from June 12 to July 14, 1919, climbing to the nest daily and often more than once a day. As a result of his observations, has has given us a full, accurate, and detailed account of the home life of these birds, to which the reader is referred for details. Although the locality was near the city, it was not strictly urban, for a woodland area of mixed deciduous and coniferous trees, which was two or three square miles in extent, aproached to within about 30 feet of the nesting-tree. He describes the nest as follows:

About four feet from the top of a young Rock Maple which was one of a row of such trees a small twig sprang at a considerable upward incline from the south side of the main stem of the tree, which was here one and one-fourth inches thick. The twig itself is one-fourth of an inch in thickness, and at a distance of one and one-eighth inches from the main trunk it divides at an angie of fifty degrees Into two nearly equal parts, each of which is about five inches long and ends in a cluster of leaves. The pensile nest, which was well hidden and shaded by foliage, was hung from the fork between these two small twigs, at a height of twenty-four feet, eight inches, from the ground. Although the lower part of it is roughly circular, the rim is “gathered” to the twigs, so that the opening is shaped like a sector of a circle, with the two twigs as radii, and the outer rim as the arc of the sector. The acute angle between the twigs is filled in for about three-quarters of an inch with nesting material. The “gathering’ of the rim of the nest, causing the walls to be indurved at the top, must have been efficacious in retaining eggs and young within it when it tossed and swayed in the breeze, as it did very much In the slender top of the tree. * * * The outside of the nest is composed of fine strips of the outer hark of White Birches, dead grass blades, coarse xvhite hen feathers, hits of frayed white twine, one spider’s white “cocoon,” and much spiders’ web. The birch bark is much the most conspicuous material. Ends of strips of it have been left loose, so that they flutter in the breeze, breaking up the outline of the nest and helping to conceal it. At points where strips of birch bark cross one another they sometimes seem to possess mutual adherence without visible binding material, as though they had been gummed together, perhaps by the bird’s saliva. The nest Is fastened to the twigs by spiders’ web, strips of birch hark, string, and grass blades. The interior is lined chiefly with fine dead grass stems and flower spikelets, but the lining includes also one or two needles of the White Pine and several white hen feathers, finer than those on the outside of the structure.

The building of the nest was apparently well under way when Dr. Lewis first noticed the birds on June 11, and on June 15 the nest held the first egg. Both birds secmed interested in the construction of the nest, but, as he usually could not distinguish between the sexes, he was not sure that the male did any work on the nest.

Charles E. Doe has sent me his notes on a Philadelphia vireo’s nest that he found on a small island at the north end of Moosehead Lake, Maine, in July 1907. On July 7 he saw both birds working on the nest, 35 feet from the ground, attached to a lower limb of a big yellow birch on the edge of some dense spruce timber; there was no other birch in the vicinity. When lie found the birds building, on July 7, they had woven only a few strands close up in the crotch of the twig; two days later it was nearly finished, and on the 10th it was all done. On July 15, he wrote in his notes: “The first egg must have been deposited on the 12th, for I climbed to the nest for the first time on the 13th, when it contained two eggs and the bird was on the nest; today, when I climbed to it, she sat very close and allowed me to part the leaves that partly hid the nest; I watched her fully five minutes and then she flew only when I put my hand within six inches of her. Up to then, she had simply raised her head and watched me closely; and how pretty she was with her yellowish white throat! When she flew, she kept out of sight for about ten minutes, and then returned and moved about in a nearby tree, but did not scold as vireos do.”

He found another nest in the same locality on June 29, 1909. This was 40 feet from the ground in a thick maple, a lone tree among spruces, on the edge of heavy spruce timber at the top of a ravine. Both nests contained full sets of four eggs each.

Mr. Terrill has sent me a photograph (pl. 45) of a nest that he found 8 feet from the ground in an alder along a small stream; this nest had some birch bark in its composition, as well as a quantity of usnea, which can he seen hanging below the nest; he says that the use of usnea in the nest is diagnostic.

Eggs: From three to five eggs may constitute a full set for the Philadelphia vireo, four being the commonest number and five very rare. These are very much like the eggs of the red-eyed vireo, though slightly smaller. Mr. Brewster (1903) describes his eggs as “elongate ovate in shape and pure white, sparsely spotted with burnt umber, chocolate and dull black.” Philipp and Bowdish (1917) say that their eggs “were white with dark brown spots and specks, the larger spots tending to have a rusty border”. Mr. Doe’s eggs are marked on the large end with dark reddish brown. The scanty markings are sometimes scattered over the whole surface, but more often nearer the larger end of the egg. The measurements of 50 eggs average 19.2 by 14.0 millimeters; the eggs showing the four extremes measure 21.7 by 14.9, 21.6 by 15.3, 17.8 by 14.0, and 18.5 by 18.0 millimeters.

Young: Dr. Lewis (1921) found the incubation period for the Philadelphia vireo to be about 14 days. He saw the male relieve the female and sing while incubating on the nest. Mr. Brewster (1903) also saw the male singing on the nest. In the nest that Dr. Lewis studied the first egg hatched on June 29; during that afternoon the pair changed places on the nest at very frequent intervals. “During the hour and twenty-five minutes between 12.40 p. m. and 2.05 p. m. the pair had exchanged places on the nest eight times, the intervals between reliefs being sometimes as short as three, four, or six minutes.”

The remaining three eggs hatched during the following two days. “It will be noted that the first, second, and third young birds were hatched in fourteen days after the laying of the first, second, and third eggs, respectively. The time required for the incubation of the fourth egg lies somewhere between thirteen days, three hours, twenty-eight minutes and thirteen days, eleven hours, sixteen minutes [between times of examination]. If all the eggs were warmed alike when a bird was incubating, and if the several eggs required equal amounts of incubation to cause hatching, it would appear that incubation began as soon as the first egg was laid, but that it was more broken and ineffective between the laying of the third and the fourth eggs than at other times.”

He gives the following brief outline of the chief events at the nest:

June 15. First egg laid.

June 18. Fourth (last) egg laid.

June 29. First egg hatched.

July 1. Third and fourth eggs hatched.

July 3. First cries of young heard.

July 12. Three oldest nestlings left nest.

July 13. Fourth nestling left nest.

July 14. Last observation of nestlings (two only).

On July 6: “Between 12.51 p. m. and 2.35 p. m. the young were fed at 12.52, 1.17, 1.20, 1.28, 1.39, 1.46, 1.52 (twice), 1.54 (twice), 2.20, 2.27 and 2.29, a total of thirteen feedings in one hour and forty-four minutes. I have recorded txvo feedings at 1.52 p. m. because at that time I saw the two parent Vireos stand on opposite sides of the nest and both feed the young at once. At 1.54 both birds were in sight near the nest at once and they fed the young in quick succession. At 1.20 and again at 1.52 one of the old birds, after feeding the young, removed excrement from the nest and flew away with it. The young birds were brooded from 12.52 to 1.16, from 1.28 to 1.36, from 1.39 to 1.46, and from 2.29 to 2.35, when I departed for a few minutes.”

For an early morning feeding period, he made the following record: “Between 4.00 a. m. and 7.00 a. m. the young were fed at the following times: 4.06, 4.17, 4.29, 4.31, 4.38, 4.39, 4.40, 4.42, 4.45, 4.48, 4.49, 4.50, 4.52, 4.55, 4.56 (twice), 5.30, 5.54, 5.55, 6.00, 6.02, 6.03, 6.04, 6.05, 6.09, 6.12, 6.15, 6.18 (twice), 6.21, 6.28, 6.30 (twice), 6.32, 6.35, and 6.51, a total of thirty-six feedings, or nine for each young bird, in the first three hours of morning activity. * * * Between 4.05 and 4.57 there were sixteen feedings, between 4.57 and 5.53 there was one feeding only, and between 5.53, and 6.53 there were nineteen feedings. It will be observed that the feedings exhibit a marked periodicity, as though the young were given regular meals, with intervals of comparative rest.” He noted other evidences of periodicity at other times, and saw some evidence that the parents were not satisfying their own hunger during the periods of rest. “Food which I saw the adult Philadeiphia Vireos take to their young consisted largely of naked caterpillars, brown, green, and whitish, and of flying insects of various kinds.”

For two or three days before the last nestling finally left the nest the young birds were more or less restless and frequently hopped about in the tree or fluttered down to the ground, or even made short flights. They were often rescued from the ground and placed in the tree or returned to the nest. At such times the parents were quite excited and aggressive; Dr. Lewis says: “I climbed the tree again and, as I drew near the youngster, one of the parents dashed at me, crest erect, scolding loudly and rapidly. This was continued until I left the tree and was the first scolding I had received from an old bird when I was in the tree.”

Dr. Dwight (1897) writes:

It is evident that but one brood is raised in a season. I have seen young birds as early as July 7, comical little chaps largely bare skin and the promise of a tall. At this tender age they are unwilling to essay flight except when urged by anxious parents to make a clumsy, flying leap from one twig to another, but they are knowing enough to keep quiet when they hear a crashing in the bushes, and as they become older they lose no time in moving quickly away. I have found them in alder thickets or along some of the bushy cattle paths which end abruptly at steep walls of rock or lose themselves In small clearings. In fact I never could tell when or where I might run across the birds, young or old, but during the latter part of July, when the moult is in progress, it is almost impossible to find them anywhere.

Plumages: Dr. Dwight (1900) describes the natal down as “pale drab-gray.” And he says that the juvenal plumage is “similar to V. o~ivaceus and V. gilvus, but darker above and distinctly yellow below. Above, wood-brown, darker and olive tinged on the back and wing coverts. Wings and tail clove-brown with olive-green edgings. Below primrose-yellow, auriculars, orbital ring, and superciliary stripe buffyellow. Lores and postocular streak dusky.”

An incomplete postjuvenal molt, involving the contour plumage and the wing coverts, but not the rest of the wings or the tail, begins at the end of July This produces a first-winter plumage, which is practically indistinguishable from the winter plumage of the adult. Dr. Dwight describes this as “similar to the previous plumage but greener with a grayer crown, and brighter yellow below. Above, dull olivegreen, slate-gray on the pileum. Below pale canary-yellow, whiter on middle of abdomen. Sides of head pale greenish or grayish buff, superciliary stripe paler; transocular streak dusky.” He says that the adult, at this season, is usually paler yellow below with a larger area of white on the abdomen.

There is apparently no prenuptial molt, but specimens taken at the proper season to show it are not available. The sexes are practically alike in all plumages.

Food: Of the 84 stomachs of the Philadelphia vireo in the collection of the Biological Survey, Dr. Edward A. Chapin (1925) found that only 75, taken in May, June, and September, contained enough food to show the percentages.

All but 4.34 percent of the animal food consisted of insects, the remainder being spiders. Lepidoptera formed the largest item, 24.13 percent of which were caterpillars and 2.17 percent adult moths and butterflies; in September the percentage of these lepidopterous items rose to 45.53, or nearly half of the entire food for the month.

Coleoptera ranked next, 24.82 percent for the year. “The beneficial beetles eaten are almost all of the family Coccinellidae, or ladybirds, well-known as enemies of plant lice and scale insects. Thirteen species of ladybirds have been identified from stomachs of the Philadelphia virco, and these make up a little more than a fifth of all the beetles consumed, or about 5 percent of the total food.” This is a bad showing for this vireo, but it is more than offset by all the injurious beetles destroyed, such as leaf-eating beetles (Chrysomelidae), 7.99 percent; weevils (Rhynchophora), 3.43 percent; wood-boring beetles (Buprestidae and Cerambycidae) and the plant-feeding Elateridae, together, less than 1 percent. The mildly beneficial dung beetles and the leaf-chafers (Scarabaeidae) taken together amount to 6.94 percent.

Of the Hymenoptera, “approximately 14 percent of the annual subsistence of the Philadelphia vireo is composed of wasps, bees, and related insects. Here are to be found some of the most beneficial of all insects, the parasitic ichneumon flies and the minute chalcids. On the other hand, the kinds of ants eaten are usually injurious, especially the large, black, carpenter ants (C’amponotus ,4erculeanus), and even if some of them do no direct damage they are indirectly injurious in fostering plant lice.”

Flies (Diptera) form 11.76 percent of the food, including midges and both injurious and beneficial forms. True bugs (Hemiptera) make up 10.46 percent of the annual food, including the injurious stink bugs but not the useful stink bugs or the beneficial assassin bugs, so that the score is good in this group. Other insects amount to only 1.14 percent.

The seasonal average of vegetable food was but 7.22 percent of the whole, although in September it amounted to 18.71 percent. The fruits identified were bayberries, wild rose hips, and wild grapes, but no cultivated fruits or seeds were found.

Dr. Lewis (1921) says of the feeding habits of this virco:

The birds fed usually in the border of the woods, among the lower limbs of the Red Oaks and Red Maples, less often among the White Birches or the Rock Maples. The pair which resided among the White Birches a hundred yards behind my house probably fed among them.

I found the Philadelphia Vireos to be rather more active in their feeding habits than are the Red-eyed Vireos. The trick mentioned by Dwight of hanging backdownward, like a Chickadee, from a cluster of leaves while picking insects from it was observed frequently, but the majority of the food of this species seemed to be taken while the birds were on the wing. They would leap repeatedly into the air to snap up passing insects with distinct “click’s” of the bill. At other times they were seen hovering like Kinglets before branch-tips while they gathered food therefrom. The work done by this pair of Philadelphia Vireos must have aided greatly in keeping the trees in their vicinity free from insect pests this summer.

Behavior: Much of the normal behavior of this vireo is described in Mr. Brewster’s remarks under “Spring” and in Dr. Lewis’s account of its feeding habits above. But Dr. Lewis (1921) wrote on July 3, describing a rather unusual performance:

Observation began at 6.16 a. in., when one bird was on the nest, while no song of the species was to be heard. No change was noticed until 6.24 a. in., when the male began singing among the oaks. A moment later, still singing, be flew to a perch near the nest. The next instant there was a series of excited squeskings, and both birds were away in a mad chase, fighting at frequent intervals with one another, apparently without mercy. They would circle around and around, passing repeatedly through the nesting-tree, then turn face to face in the air and struggle furiously, with much fluttering of wings and sharp clicking of bills, until often they fell nearly to the ground. After the first few seconds the squeskings stopped and shortly afterward the male began to sing as he fought. As the birds passed through the tree they would sometimes alight for a moment, two or three feet apart. After the briefest of pauses the female would attempt to fly hack to the nest, when the male would dash after her again and the fight would be resumed.

Voice: Every observer seems to agree that the song of the Philadelphia vireo closely resembles that of the red-eyed vireo, yet there is a subtle difference that a practiced ear cnn detect, especially if the two are heard at the same time. Mr. Brewster’s (1880) first impression follows:

Contrary to what might he expected from the apparently close relationship of the two birds, the song of this species does not in the least resemble that of Vireo gilvas. It is, on the other hand, so nearly identical with that of V. oUreceas that the most critical ear will, in many cases, find great difficulty in distinguisbing between the two. The notes of pbfledelphicus are generally pitched a little higher in the scale, while many of the utterances are feebler, and the whole strain is a trifle more disconnected. But these differences are of a very subtile character, and, like most comparative ones, they are not to be depended upon unless the two species can be heard together. The Philadelphia Vireo has, however, onc note which seems to he peculiarly its own, a very abrupt, doublesyllabled utterance, with a rising inflection, which comes in with the general song at irregular hut not infrequent intervals. I have also, on one or two occasions, heard the male, when in pursuit of his mate, utter a soft psero, similar to that sometimes used by Virco oliveccus and both sexes when excited or angry have a harsh, petulant note exactly like that of V. gUy us.

Referring to the “double-s~llabled utterance” mentioned by Mr. Brewster, Dr. Dwight (1897) says:

I would merely emphasize the fact that it Is the essence of the song and enters into it at as regular intervals as any of the other notes. It is a liquid note, beginning the song and occupying about three fifths of a second for the two syllables of which it is composed, on both of which considerable emphasis is laid. There seems to be a slight trill or ripple between the syllables when heard close at hand and the inflection rises slightly on the latter. A pause follows, approxtmating one and two fifths seconds, and the first note is again repeated, less forcibly and slightly varied. Again the pause ensues, and now it is followed by a triple note, not interrogatory and indistinguishable from one of V. olireceas. Again the pause, this time followed by a repetition of the triple note, slightly varied so as to lose some of its sibilance, and after the customary pause of one and two fifths seconds, the song is repeated from the beginning, nearly eight seconds having elapsed in completing one cycle. The four notes may be suggested by the syllables chuir-r’wd, chfir-wd, pst’-1-rJ, psr’-r-rii. * * * The speed at which the song flows is an interesting factor and is remarkably uniform for each individual songster,: in fact, I could almost Identify certain Philadeiphias and Red-eyes by timing their songs. V. phuladelphicus sings at the rate of from twenty-txvo to thirty-six notes a minute, averaging a trifle over twenty-six, while V. olzvaccas rattles on at the rate of from fifty to seventy, their song rate averaging a trifle over fifty-nine. * ï * The male Vireos are in full voice during June, hut toward the end of the month the song period rapidly wanes, and after the first days of July their notes are not very often heard save as a subdued warble at rare intervals.

Also referring to Mr. Brewster’s “double-syllabled utterance,” Philipp and Bowdish (1917) write: “In our experience with the birds, this distinctive song absolutely predominated with the general impression of a song quite distinctive from that of the Red-eye, or, in fact, of any other Vireo we had heard.

“These birds have the common scolding note characteristic of Vireos, but, in addition, they gave voice to several rather musical, but apparently protesting notes. In one instance, the female sung a subdued but musical reply to the song of her mate who was at a little distance from the nest on which she sat.”

Dr. Lewis (1921) also says that it is certain that the female can sing, and that her song is sometimes, at least, made up of notes differing from any heard from the male. “The only songs which I know with certainty were uttered by the female are two loud ‘Doodle-ee l’s,’ a few very low notes, and the song xvhich she sang just after laying her last egg on June 18. This latter song was very sweet, clear, and simple, and was sung slowly for eight minutes in a low voice. It consisted of a variety of notes, such as ‘Hbllit; ee-db-it; w?ty-wer; ee-ch~w-ee; doo-we’?; hhllit-whew I’, uttered over and over in a different order each time. The effect was charming.”

He seems to differ from Dr. Dwight in the rapidity of the song, for he says: “On June 21 I counted for five minutes the song utterances of a bird which was singing this song [the one mentioned below] among the oaks, and found the number of utterances per minute to be seven, seven, nine, eleven, and six, respectively. A similar count for one minute on June 22 of the utterances of a bird singing this song from the nest showed seventeen utterances to the minute, which I consider to be quite the highest rate at which I heard this song delivered.” The discrepancy is perhaps due to the fact that lie was counting complete songs, while Dr. Dwight was counting individual notes.

He says, of the song he counted: ï The song heard from the male from June 13 to June 22, inclusive, was simple, but delightful; a low, sweet, gentle “Duo-we? whed-hooey; doo-we? whe&hooey,” uttered slowly and with long intervals between one utterance and the next. Sometimes the first utterance was elaborated into “Doodle-eeT’. * * * On June 23, and often thereafter, the male Philadelphia Vireo sang a song altogether different from that which I have described. This new song was loud and vigorous, and was readily recognizable as a Vireo’s song, although the tone In which it was given was not quite so full as is the tone of the song of the Red-eyed Vireo. It consisted of notes like “S-s-s-cApe I ee-~h-yuh! ee-ybit! chAeh-ly I’, and perhaps one or two others, repeated over and over in different orders. * * * On June 25, when the female had left incubation to feed, the male, while following her through the lower branches of the trees, sang, in a loud voice, “Chee-Ow-y! hee-flh I,” over and over again. This song was heard at such times only. Other loud songs which were heard often from this male after June 23 were “Whte-hoit! s-s-s-jArry I,’ and “S-s-s-chAw-ee! whAe-hooey I” After July 4 sInging rapidly declined, the lait song heard from this species being a few loud notes on July 17, three days after I ceased to find the juvenals. * * * Other Philadelphia Vireos heard daring the nesting-season sang similar loud songs, but the songs of no two of them were exactly alike. * * * I might point out that many common song-phrases of the Red-eyed Vireo, such as its plain little “Huh-huh,” do not appear in any recognizable form in the songs of the Philadelphia Vireos heard by me, and that this seems to provide one ready means of distinguishing between the songs of the two species.

He mentions, also, “a mouse-like squeaking, a scolding note, a fine 7 * * * ‘It, it, it, it, it,’ and (from the female only) a ‘Mew, mew. The ‘Mew, mew’ of the female apparently indicated readiness for coition.”

Field marks: A glance at the excellent colored plate published with Dr. Dwight’s (1897) paper will show that the Philadelphia vireo looks very much like a warbling vireo with a pale yellow breast but slightly greener above and with the stripe over the eye less distinct. It also looks like a red-eyed vireo, minus the gray cap, distinctly bordered with dusky, and with more yellow beneath. The yellow throat and breast of the yellow-throated vireo are a much deeper yellow, and there are two white wing bars on each wing. From the warblers, some of which have a similar color pattern, it can be distinguished by its heavier bill and stockier shape.

Enemies: We do not know much about the enemies of this vireo. Dr. Friedmann (1934 and 1943) could find only two cases where it was parasitized by cowbirds, one in Alberta and one in Ontario, by the Nevada cowbird and by the eastern cowbird, respectively. Probably cowbirds are not too common in the regions where it breeds. Predators doubtless destroy some eggs, young and adult birds, but this apparently has not teen observed. Accidents may account for some mortality.

Fall: Mr. Brewster (1830) draws this attractive picture of the fall mwration in Maine:

At the close of the breeding season, when the brakes are turning brown, and occasional maples along the lake shore begin to glow with the burning tints of autumn, the Philadelphia Vireos join those great congregations of mingled Warbiers, Sparrows, Woodpeckers, Titmice, etc., which at thIs season go trooping through the Maine woods. The specimens taken at Upton, in 1874, were in flocks of this kind, and several of them were shot in low bushes, an apparent exception to the rule previously given. But mixed society among birds, as well as men, Is a great leveller of individual traits, and it is by no means uncommon on these occasions to find such tree-loving species as the nay-breasted, Cape May, Blackburnian, and Blue Yellow-hacked Warbiers, the Red-bellied Nuthatch, the Goldencrested Kinglct, and many others, consorting with Winter Wrens, Water Thrushes, and Canada Flycatchers in the thickets by wood-paths, or along the banks of ponds or rivers; and I know of no more interesting sight, especially if it be a bright September morning, before the sun has risen above the trees. The dark foliage of the alders and vihurnums is frosted with innumerable dewdrops, which fall in sparkling showers where a Warbler hops or a Woodpecker taps on the slender stems. Yellow and gold and scarlet liveries flash among the glossy leaves, as the active little forms appear and disappear, while the constant rnstling and low-toned conversational chirping from the depths of the thicket suggest all sorts of pleasing mysteries. It is a pretty picture, this gathering of the birds in the quiet depths of the forest.

Winter: The Philadelphia vireo spends the winter in Central America. Dickey and van Rossem (1938) call it a “common winter visitant at the upper limits of the Arid Lower Tropical Zone both along the interior and coastal mountains” in El Salvador. Where usually seen, “the altitude was 3,500 feet, and, curiously enough, the species was never seen at any other altitude, even though apparently identical conditions prevailed for at least 500 feet lower. In relative numbers, philadelplticus was slightly more common than gitvns and lnvariably outnumbered the latter when especially favorable trees brought the two species together. Sometimes as many as a dozen philadeiphicus could be found in a single food tree, but otherwise the species was, like most vireos, solitary.”

Range: Central Canada to Panama.

Breeding range: The Philadelphia vireo breeds north to northeastern Alberta (Chippewyan) ; central Saskatchewan (Prince Albert); southern Manitoba (Duck Mountain and Winnipeg, and has been recorded in summer at Churchill) ; central Ontario (Lac Seul, Moose Factory, Lowbush, and Lake Timiskaming); southern Quebec (Blue Sea Lake, probably Quebec, Tadousac, and the Forillon Peninsula, Gasp~ County); and southwestern Newfoundland (Tompkins). East to Newfoundland. South to Newfoundland (Tompkins); northern New Brunswick (Tabusintac, Chatham, and Edmundston); northern Maine (probably Sourdnahunk Lake, and Moosehead Lake); northern New Hampshire (Lake Umbagog and Dixville Notch and possibly Franconia); probably northern New York (Adirondack region); northern Michigan (Sault Ste. Marie); northern North Dakota (Turtle Mountains); eastern Montana (Johnson Lake, probably migrating) ; southern Saskatchewan (Crescent Lake); and southern Alberta (Red Deer). West to central and eastern Alberta (Red Deer, Camrose, Lac la Biche, and Chippewyan).

Winter range: The winter home of the Philadelphia vireo is in Central America from northern Guatemala (Volc~n de Agua and Secanquim) through El Salvador (Mount Cacaquatique); and probably western Nicaragua; the higher portions of western Costa Rica (Liberia, San J05~, Guayabo, and the valley of El General); to western Panama (VolcAn de Chiriquf, Cocoplum, and Altoc Cacao on the Azuero Peninsula). A specimen from Cozumel Island, Mexico, was recorded by 0. Salvin in the This for 1888 as taken in January “during the last two years.” It was probably accidental at that date.

Migration: Late dates of spring departure are: Costa Rica: San Jos6, April 23. Veracruz: Presidio, May 10. District of Columbia: Washington, May 30. West Virginia: Wheeling, May 24. New York: Geneva, June 5. Mississippi: Deer Island, May 7 (possibly accidental). Texas: Kemah, May 19. Kentucky: Lexington, May 16. Ohio: Youngstown, June 7. Missouri: Grandin, May 24. Illinois: Lake Forest, May 28. Wisconsin: Madison, May 29. Minnesota: Duluth, June 2. South Dakota: Sioux Falls, May 31.

Early dates of spring arrival are: Florida: Pensacola, April 18. District of Columbia: Washington, May 4. Pennsylvania: Doylestown, May 2. New York: Buffalo, May 3. Massachusetts: Lincoln, May 16. Maine: Dover-Foxcroft, May 12. Quebec: Hatley, May 12. New Brunswick: Oromocto, May 18. Arkansas: Winslow, April 24. Missouri: St. Charles, April 26. Tennessee: Memphis, May 2. Kentucky: Versailles, April 30. Ohio: Oberlin, April 26. Ontario: Ottawa, May 13. Michigan: Ann Arbor, ~Iay 10. Iowa: Des Moines, May 10. Wisconsin: Madison, May 10. Minnesota: Minneapolis, May 12. Texas: Galveston, April 9. Nebraska: Lincoln, May 16. North Dakota: Fargo, May 24. Manitoba: Margaret, May 15. Saskatchewan: Regina, May 19. Alberta: Chippewyan, May 23.

Late dates of fall departure are: Alberta: Camrose, September 8. Manitoba: Aweme, September 19. Wisconsin: Appleton, September 30. lowa: Giard, October 1. Louisiana: New Orleans, October 29. Texas: Dallas, October 20. Ontario: Ottawa, September 23. Michigan: Detroit, September 24. Ohio: Columbus, October 12. Illinois: DeKaib, October 10. Tennessee: Nashville, October 10. Mississippi: Bay St. Louis, October 15. Maine: Phillips, October 2. New Hampshire: Dublin, September 29. Massachusetts: Springfield, September 24. New York: Schenectady, October 1. Pennsylvania: McKeesport, October 5. District of Columbia: Washington, October 5. West Virginia: Bluefield, October 2. North Carolina: Swannanoa, October 2. Georgia: Atlanta, October 9. Florida: Pensacola, October 8. In the Atlantic Coast States this species is apparently more common in fall than in spring.

Early dates of fall arrival are: Minnesota: Lanesboro, August 18. Wisconsin: Madison, August 22. Iowa: Forest City, August 31. Michigan: Detroit, August 28. Ohio-Toledo, August 29. Illinois: Glen Ellyn, August 21. Kentucky: Versailles, August 28. Mississippi: Gulfport, September 19. Louisiana: Thibodaux, August 15. New Hampshire: Jaffrey, August 25. Massachusetts: Harvard, September 5. New York: Rochester, August 28. Pennsylvania: Jeff ersonville, September 9. District of Columbia: Washington, September 2. Florida: Pensacola, September 28. Guatemala: La Montanita, October 18. Nicaragua: Escondido River, October 21. Costa Rica: San Jos6, October 21. Panama: Cocoplum, Bocas del Toro, October 29.

Casual records: There is only a single record each for Kansas and Montana, though it is quite possible that this vireo is a fairly regular migrant through both States. In Kansas specimens were collected September 2 and 24, 1922, in Doniphan County; and in Montana one was collected on June 3, 1910, near Johnson Lake, Sheridan County.

Egg dates: Maine: 4 records, June 15 to July 15.

Manitoba: 3 records, June 9 to 14.

New Brunswick: 8 records, June 15 to 24.

Quebec: 2 records, June 18 and 26

About the Author

Sam Crowe

Sam is the founder of He has been birding for over 30 years and has a world list of over 2000 species. He has served as treasurer of the Texas Ornithological Society, Sanctuary Chair of Dallas Audubon, Editor of the Cornell Lab of Ornithology's "All About Birds" web site and as a contributing editor for Birding Business magazine. Many of his photographs and videos can be found on the site.

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