Part 16

Dr. J. C. Merrill (1888) calls them "restless, shy, and very difficult to shoot", and says further, "When alarmed, as they very easily are, the males move rapidly through the trees, often flying a hundred yards or more at once, and were it not that their constant song indicates their movements, it would be impossible to follow them. I have frequently followed one for half an hour or more before I could even catch a glimpse of it, and my pursuit of any particular one was more often unsuccessful than the reverse. * * * I have never found a land bird more wary and difficult to shoot. But as soon as the young leave the nest this extreme shyness disappears, and the parents are readily approached and observed as they busily search for food for their young family."

Dr. William T. Shaw, who collected a specimen of this warbler in northwestern Washington, says in his notes: "This warbler, a singing male, was noticeably a percher upon high, isolated cedar poles when singing, having three or four favorite ones in his territory, which was a hillside grown to a height of about 15 feet with second-growth deciduous trees, following fire. He sang from a height of from 30 to 40 feet up near the top of these old widely-scattered, fire-blasted, weather-bleached trees, clearly out in the open and isolated from green sheltering foliage beneath him, in such a location as one is accustomed to seeing lazuli buntings perch when they sing." Dr. Shaw thought the first part of the song suggested that of Macgillivray's warbler, and the latter notes reminded him of "those heard among the inspirational notes in the song of the lazuli bunting."

The Bowles brothers (1906) say that, in the spring, the males have at times a very pleasing habit while singing, "that of hovering thru the air for a distance of fifteen or twenty yards. The manner of flying at these times is very slow and closely resembles that of one of the marsh wrens, but the beak is turned upwards and the feathers on the swelling throat separate until it seems almost certain that the bird will sing himself into some serious bodily mishap."

VERMIVORA VIRGINIAE (Baird)

VIRGINIA'S WARBLER

PLATE 18

HABITS

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, Ridgway (1877) first observed this warbler "among the cedar and piñon groves on the eastern slope of the Ruby Mountains. * * * On the Wasatch and Uintah Mountains it was more abundant, being particularly plentiful among the scrub-oaks on the foothills 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, piñon-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 piñons close to creeks; singing in dead shrub 10 feet high at base of rock slide; in aspen; in thickets of sage, elder, _Ephedra_, 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 _virginiae_, together with other migrating warblers, 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 Huachuca 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 bark, 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 3-1/2 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 vinaceous-drab." 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 male.

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 warblers 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 follows: "The male is very musical during the nesting season, uttering his _swee_ 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 fullness 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 _ché-we-ché-we-ché-we-ché-we, wit-a-wi't-wi't-wi't_ (these terminal notes being partially characteristic of _Helminthophagae_) and _che-wé-che-wé-che-wé, ché-a-ché-a-ché_". Dr. Linsdale's (1938) comments on singing males follow:

The song varied from 7 to 10 notes, being usually 8, and it occupied about 3 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 cañon 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 _zdl-zdl-zdl-zdl, 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's warblers.

DISTRIBUTION

_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 Colorado (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 Amarilla, 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. Colorado--Estes Park, May 2. Arizona--Madera Canyon, Santa Rita Mountains, April 2. Utah--Vernal, 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.

VERMIVORA CRISSALIS (Salvin and Godman)

COLIMA WARBLER

CONTRIBUTED BY JOSSELYN VAN TYNE

HABITS

Described in 1889 from a single specimen collected by W. B. Richardson in the Sierra Nevada de Colima, Mexico, this handsome warbler was, in 1932, still known from only a dozen museum specimens, and not a word had been recorded on its habits. In that year a University of Michigan expedition found the Colima warbler to be common in the higher forests of the Chisos Mountains of southwestern Texas and made the first discovery of its nest and eggs. The basis for the inclusion of this warbler in the A. O. U. Check-List had been a single specimen collected by Frederick M. Gaige in the Chisos in 1928 (Van Tyne, 1929).

The range of the Colima warbler has been recorded only very sketchily, but Bangs (1925) was probably correct in surmising that the specimens from southern Mexico (Colima and Michoacán) were migrant birds. The closely related Virginia's warbler, which nests in the Rocky Mountain States, winters mainly in Michoacán, Guerrero, and Jalisco. Recently R. T. Moore (1942) added a second, more southerly, locality in Michoacán and one in eastern Sinaloa to the known southern range of the Colima warbler. The breeding range is apparently restricted to the highlands of northeastern Mexico and the Chisos Mountains of southwestern Texas. In Texas the Colima warbler occurs at altitudes between 6,000 and 7,500 feet (Van Tyne, 1936); in Coahuila, apparently, only above altitudes of approximately 7,500 feet (Burleigh and Lowery, 1942). Records from the southern part of its range, however, show a greater altitudinal spread. The type specimen was taken in Colima at about 8,000 feet, and R. T. Moore (1942) reports two November specimens, one taken at 9,500 feet in northeastern Michoacán, the other at 5,200 feet in Sinaloa. These represent the extremes of the known altitudinal range.

_Courtship._--Mating behavior has been observed during the first few days of May and sets of eggs noted May 15 (just completed) and May 20 (highly incubated). The only recorded specimen in juvenal plumage was collected July 20. Peet observed pursuit behavior in the Chisos Mountains on May 4 (within a few days of nest building), which may have had some courtship significance, but nothing definite is known of the courtship habits. Sutton noted copulation twice on May 1 in the Chisos, and the gonads of specimens collected that day were much enlarged; there was no indication that the females had begun incubating.

_Nesting._--Two nests, both in the Chisos Mountains, have been described. The first (discovered in 1932) was lodged between small rocks and deeply imbedded in dead oak leaves on the sloping bank of a dry stream bed. A dense ground cover of vines and other herbaceous plants arched completely over it, leaving an entrance only on the northwest side, toward the stream. The nest had a basic structure of loosely woven fine grasses, the outside reinforced with pieces of green moss and the rim with strips of cedar bark; the cavity (5 centimeters across the rim and 4 centimeters deep) was lined with fine grass, a little fur, and a few hairs (Van Tyne, 1936). The other nest, which was "on the ground, under a little bunch of oak leaves, at the edge of a talus slope, almost at the very base of the cliffs" (Sutton, 1935), was similar, but its basic structure included dry leaves, and the site was concealed by only a partial canopy of leaves (Van Tyne and Sutton, 1937).

Nest building was observed in the Chisos Mountains on May 7, 1932 (Van Tyne, 1936):