VERMIVORA VIRGINIAE (Baird)
This warbler was discovered by Dr. W. W. Anderson, at Fort Burgwyn, New Mexico, and was described by Baird, in a footnote in The Birds of North America, by Baird, Cassin, and Lawrence (1860). The footnote occurs under the explanation of plates in the second volume. The warbler was named for Mrs. Virginia Anderson, wife of the discoverer.
Its range during the breeding season covers portions of Nevada, Utah, Colorado, Arizona, and New Mexico, mainly in the mountain regions, and it retires to Mexico for the winter. It seems to be more abundant in Colorado than elsewhere, breeding from the foothills, where it is a characteristic bird and perhaps the most abundant of the wood warblers, up to 7,500 to 8,000 feet in the mountains. On the spring migration, it is abundant along the valley streams, among the cottonwoods and willows, or sometimes among the pines; but in the summer it is found among the low scrub oak brush on the hillsides.
Bailey and Niedrach (1938) write attractively of Virginia's warbler in its Colorado haunts:
In the broken prairie where the yellow pines have taken their stand upon the crest of the tableland, and in the rocky canyons clothed with the scraggly scrub oaks slipping down to narrow grass-grown creek-bottoms, Virginia's Warbler chooses its nesting grounds.
Plants seem to burst into life during the early weeks in May. * * * The flowers of the scrub oaks tinge the hillsides with a greenish-yellow bloom; the green of bursting leaves and grasses soon blends with the nodding blossoms of the pasque-flower; the beautiful pink plume sways on the hillside, and yellow blossoms of the Oregon grape thrust forth among the holly-like leaves, making one think of flowering Christmas wreaths. It is then that the Virginia's Warblers are at the height of their activity. Their colors are the grays and yellows of the new vegetation. The males perch among scrub-oak branches and yellow pines, where they are usually concealed, and do their utmost to outsing their towhee neighbors.
In Nevada, IRidgway (1877) first observed this warbler "among the cedar and pifion groves on the eastern slope of the Ruby Mountains. * * * On the Wahsatch and Uintah Mountains it was more abundant, being particularly plentiful among the scrub-oaks on the foot-hills near Salt Lake City. They lived entirely among the bushes, which there were so dense that the birds were difficult to obtain, even when shot."
In the Charleston Mountains, Nev., according to A. J. van Rossem (1936), "the distribution appeared to be limited to the so-called Upper Sonoran associations of mahogany and Gambel oaks, and therefore the species is considered characteristic of that zone, although the extremes of altitude at which it was found were 6,300 and 9,000 feet. Because of the relative scarcity of oaks, by far the greater number were found in mahogany which here grows as low, dense forest, instead of in the more familiar shrub form in which it is usually known."
In the Great Basin region, Dr. Jean M. Linsdale (1938) found Virginia's warblers in a variety of situations, such as "in sage on rocky, pifion-covered slope 100 yards from a stream; in sage on top of ridge; at tip of mountain mahogany tree; in plum thicket; singing and foraging through upper foliage of tall birches close to creek; in cottonwoods and pifions close to creeks; singing in dead shrub 10 feet high at base of rock slide; in aspen; in thickets of sage, elder, Ephecira, and Symphoricarpos; in willow; on ground among rocks at crest of ridge." The altitudes ranged from 6,500 to 8,000 feet, with the largest number between 7,000 and 7,500 feet.
In southern Arizona, this warbler, according to Mr. Swarth (1904): proved to be very abundant during the spring migration, particularly in the lower parts of the mountains; but the most of them seem to go farther north, and but few, compared with the numbers seen in April and the early part of May, remained through the summer to breed. The earliest arrival noted was on April 10th and soon after they were quite abundant, mostly in the oak region below 5000 feet, remaining so throughout April and up to the first week In May, at which time the migrating birds had about all passed on. All that were seen after that I took to be breeding birds, for they gradually moved to a higher altitude, (6000 to 8000 feet) and were nearly all in pairs. About the middle of AprIl, 1902, I found a few viroiniae, together with other migrating warbiers, In the willows along the San Pedro River, some fifteen miles from the mountains.
Nesting: Ridgway was evidently the first to record the nest of Virginia's warbler, finding it near Salt Lake City on June 9, 1869. "The nest was embedded in the deposits of dead or decaying leaves, on ground covered by dense oak-brush. Its rim was just even with the surface. It was built on the side of a narrow ravine at the bottom of which was a small stream. The nest itself is two inches in depth by three and a half in diameter. It consists of a loose but intricate interweaving of fine strips of the inner bark of the mountain mahogany, fine stems of grasses, roots, and mosses, and is lined with the same with the addition of the fur and hair of the smaller animals" (Baird, Brewer, and Ridgway, 1874).
Shortly afterwards, a nest was found on June 1, 1873, in Colorado, by C. E. Aiken. It was reported by Aiken and Warren (1914) as "the first nest of this species known to science. * * * This was sunk in the ground in a tuft of bunch grass growing in a clump of oak brush, with the dead grass hanging over and completely concealing the nest, which was reached through a small round hole like a mouse hole through the protecting grass.~~ Dr. Linsdale (1938) reports a nest found in Nevada, at an elevation of 7,700 feet, that "was at the lower edge of a clump of grass 20 inches tall and 2 feet across. The surrounding hillside was of small rocks lying at a maximum angle of rest. A few similar grass clumps were scattered near, about 10 feet apart. The surrounding trees were mountain mahogany and chokecherry. The nest was composed entirely of grass and was in a depression in the loose soil. It was well concealed by dead grass at the base of the tuft."
In the Iluachuca Mountains, Ariz., Mr. Swarth (1904) found a nest that "was built on a steep sidehill about ten feet from a much traveled trail, and was very well concealed; being under a thick bunch of overhanging grass, and sunk into the ground besides, so as to be entirely hid from view. This was at an elevation of about 8,000 feet, which seems to be about the upward limit for this species in this region."
We found Virginia's warbler fairly common there in the middle reaches of the canyons, around 7,000 feet, and found a nest being built at the base of a bush of mountain misery; Mr. Willard collected it with a set of three eggs on June 4, 1922; it was made of leaves and strips of bark and was lined with horsehair.
Another nest before me, from the Huachucas, has a foundation of moss and lichens, dry leaves, and strips of cedar mark, over which are finer strips of the bark and shreds of dry weed stalks and grasses, with a lining of still finer fibers; it is a shallow nest, its diameter being 3 by 3'/2 inches outside and 2 inches inside.
Eggs: While 4 eggs seem to constitute the usual set for Virginia's warbler, as few as 3 and as many as 5 have been reported. These are ovate to short ovate and only slightly lustrous. They are white, finely speckled or spotted with shades of reddish brown, such as "chestnut" and "auburn," intermingled with faint specks of "pale vinaceousdrab." Some eggs are profusely spotted over the entire surface, while others have the markings concentrated at the large end. The measurements of 40 eggs average 15.9 by 12.4 millimeters; the eggs showing the four extremes measure 17.0 by 12.4, 16.0 by 13.0, 14.2 by 12.2, and 16.3 by 11.2 millimeters (Harris).
Young: On the period of incubation and on the development and care of the young we have no information except the following observations of Bailey and Niedrach (1938): "The hatching time of many species of Colorado birds seems to coincide with an abundance of larvae feeding upon plants among which the birds are nesting. We have noticed time and again, that pests are numerous upon the vegetation when the fledglings are in the nest, but a few weeks later, after the little fellows have taken wing and are able to move to other parts, the caterpillars have gone into the pupa stage." At a nest they were watching, they observed that both parents shared the work of feeding the young, averaging a trip every 6 minutes.
A. J. van Rossem (1936) took young birds that were not fully grown on July 10, and others on July 13 that had nearly completed the postjuvenal molt, from which he inferred that two broods might be raised in a season. H. S. Swarth (1904) noted that the young birds began to appear in the Huachuca Mountains about the middle of July, after which both old and young birds moved down into the foothills.
Plumages: The young Virginia's warbler in juvenal plumage is plain grayish brown above; the throat, chest, and sides are paler brownish gray; the abdomen and center of the breast white; the upper and under tail coverts are dull greenish yellow; there is no chestnut crown patch; and the greater and median wing coverts are tipped with dull buffy. The sexes are alike.
The postjuvenal molt begins early in July and is often complete before the end of that month. The first winter plumage is similar to that of the adult female at that season. In this plumage the sexes are not very different, and the crown patch is not much in evidence or is altogether lacking in the young female; both sexes are browner and with less yellow than in the adult plumage, and the female is duller than the ma1~.
A partial prenuptial molt occurs between February and May, mainly about the head, during which the chestnut crown patch is at least partially assumed and the young birds become almost indistinguishable from adults. There is, however, considerable individual variation in the advance toward maturity.
Subsequent molts consist of a complete postnuptial molt in July and August, and a partial prenuptial molt in early spring. The adult male in the fall is browner above and on the flanks, and the yellow on the chest is duller than in the spring, while the chestnut crown patch is concealed by brownish gray tips. The female, also, is browner than in the spring, with little if any yellow on the chest and with the crown patch similarly concealed. In spring birds there is much individual variation, perhaps owing to age, in the amount of yellow on the breast, throat, and chin. Some females are nearly as brightly colored as are the duller males, some have very little yellow on the chest and some lack the chestnut crown patch.
Food: Our information on the food of Virginia's warbler is limited to the observation of Bailey and Niedrach (1938) who saw a pair of these warbiers feeding their young on the caterpillars that eat the foliage of the trees and shrubs on their nesting grounds. It is significant that after these caterpillars are no longer available the warbler leaves its breeding haunts and moves down into the foothills, perhaps in search of other food; and it would be interesting to learn what that food is. It has been seen foraging on the ground, as well as in the foliage, and flying up into the air to capture insects on the wing.
Behavior: Virginia's warbler is a shy, retiring species, spending most of its time not far above the ground in the thick underbrush, where it is not easily seen, as its colors match its surroundings. It is also very lively and active, almost constantly in motion, except when it mounts to the top of some dead bush or small tree to sit and sing.
Voice: Dr. Chapman (1907) quotes C. E. Aiken as folloxvs: "The male is very musical during the nesting season, uttering his 811256 ditty continually as he skips through the bushes in search of his morning repast; or having satisfied his appetite, he mounts to the top of some tree in the neighborhood of his nest, and repeats at regular intervals a song of remarkable fulness for a bird of such minute proportions." Henry D. Minot (1880) calls the "ordinary note, a sharp chip; song, simple but various (deceptively so) ; common forms are cAS-we-ch4-'we-ch6--we-chtwe, wit-a-wii-wii-'wii (these terminal notes being partially characteristic of Hels'rtintltophagae) and ohs-toteke-tot-ohs-tot, oht-a-ohs-a-oht". Dr. Linsdale's (1938) comments on singing males follow:
The song varied from 7 to 10 notes, being usually 8, and it occupied about S seconds. At the beginning the notes were slow and they came more rapidly at the end. About half a minute elapsed between songs." Another bird "sang 14 times in 3 mInutes and 10 seconds. * * Singing perches on dead limbs that were rather exposed were the rule, but they were not often as high as the tops of tall trees. * * * On June 16, 1930, near Kingston Creek, 7500 feet, a singing male was followed for an hour, beginning at 7: 30 a. m. It sang about every 30 seconds. The territory over which it moved was surprisingly large, estimated as extending 400 yards along the caflon slope and vertically about 150 yards, from near the stream to the base of the broken cliffs. * * * The song, compared with that of the Tolmie warbler had a more rapid rhythm and the notes were thinner and weaker. It could be distinguished from that of the Audubon warbler by the lack of rising inflection at the end. The song was represented by the observer (Miller) as rdl-zdl-zdl-zdt, zt-zt-zt-zt.
Field marks: Virginia's warbler, with its plain gray upper parts, is an inconspicuous bird, and its shy, retiring habits make it difficult to observe. The chestnut crown patch is not, prominent and is often invisible. The yellow on the chest and throat of the male is quite variable and in the female and young much reduced or lacking. The best field marks are the dull yellow rump and upper and under tail covers, which are more or less conspicuous in old and young birds at all seasons.
Enemies: O. W. Howard (1899) says that "the nests of the bird, like those of other ground-nesting birds of this locality, are destroyed by jays and snakes. The jays steal both eggs and young. Often a whole band of these winged wolves will sweep down on a nest and in less time than it takes to tell it they will devour the contents and destroy the nest, the pitiful notes of the helpless parents being drowned by the harsh notes of the marauders."
Frank C. Cross writes to me that Robert J. Niedrach showed him a nest of this warbler that contained a young cowbird and one young warbler.
Winter: By the last of August or early September, Virginia's warblers have retired from their northern breeding haunts, to spend the winter in southern Mexico. Dr. C. William Beebe (1905) writes: "Occasionally in the mornings, numbers of tiny grayish warblers came slowly down the walls of the barranca, feeding as they descended, taking short flights, and keeping close to ground among the dense underbrush. These birds lingered at the camp for a time, and then, with soft, low chirps, all passed on to the water, where they alighted on the sand and drank. Then, as if at some silent signal, all flew up and returned quickly, still keeping close to the ground, zig-zagging their way upward in a long line, like tiny gray mice." These were, of course, Virginia'~ warblers.
Range: Western United States to Southern Mexico.
Breeding range: Virginia's warbler breeds north to central eastern California (White Mountains); central and northeastern Nevada (Kingston Creek, Ruby Mountains, and East Humboldt Mountains); northern Utah (Salt Lake City, Parley's Park, Packs Canyon, and Ashley) ; possibly southeastern Idaho (Joe's Gap, Bear Lake County; one specimen from Bancroft, Bannock County); and northern Cobrado (probably Little Snake River, Moffat County, and Estes Park). East to the eastern slope of the Rocky Mountains in Colorado (Estes Park, Denver, Manitou, Fountain, and Beulah); in migration has occurred east to Limon, and Monon in Baca County close to the Kansas line; and central New Mexico (Tierra Ainarilla, Lake Burford, Sandia Mountain, and Apache, probably). South to southwestern New Mexico (Apache); and southeastern Arizona (Paradise and the Huachuca Mountains). West to southeastern and central Arizona (Huachuca Mountains, Santa Catalina Mountains, and Prescott) ; and eastern California (Clark Mountain and White Mountains; casually in migration to Lemon Grove).
Winter range: In winter Virginia's warbler is found in west central Mexico from northern Jalisco (Bolanas) ; and Guanajuato (Guanajuato), to Morelos (Yautepec); and Guerrero (Talpa and Chilpancingo).
Migration: A late date of spring departure is: Sonora: Moctezuma, May 10.
Early dates of spring arrival are: Texas: Socorro, April 20. New Mexico: Cooney, April 10. Coborado: Estes Park, May 2. Anzona: Madera Canyon, Santa Rita Mountains, April 2. Utah: .Vernab, May 5. Nevada: South Twin River, April 30.
Late spring migrant in Brewster County, Tex., May 13.
Late dates of fall departure are: Utah: Vernal, September 20. Arizona: Tombstone, September 11. Colorado: Boulder, September 21. New Mexico: Koehler Junction, September 11. Texas: El Paso, September 16.
Early dates of fall arrival are: Arizona: Toprock, July 23. Texas: Toyavale, August 21. Sonora: Guadalupe Canyon, August 31.
Casual records: Two specimens of Virginia's warbler have been taken in western California: in San Diego County, on September 3, 1931; and at Prisoner's Harbor, Santa Cruz Island, on September 8, 1948. Virginia's warbler has been reported as occurring in Nebraska and Kansas, but there is no record of a specimen having been taken in either State.
Egg dates: Arizona: 10 records, May 17 to June 21; 5 records, May 25 to June 4. Colorado: 6 records, June 1 to 26. Nevada: 3 records, June 8 to 15.
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