Part 31

The Bowles brothers (1906) say that the nests are very much like those of the eastern Nashville warbler, as taken by them in Massachusetts. In Washington, "the site chosen is usually at the base of a very young oak, or fir, tho on one occasion we found one built under some blackberry vines at the base of a large fir stub. The nests are sunk well into the ground or moss, and are so well concealed as to defy discovery unless one flushes the bird."

Eggs.--The eggs of the western Nashville warbler are practically indistinguishable from those of the eastern form. The measurements of 40 eggs average 15.3 by 12.2 millimeters; the eggs showing the four extremes measure =16.6= by =13.2=, =14.3= by 11.9, and 16.0 by =11.5= millimeters (Harris).

We have no information on the incubation of the eggs or care of the young. The changes in plumage parallel those of the eastern bird. Very little seems to be known about the exact food of the Calaveras warbler, and its voice seems to be the same as that of the Nashville, but the following accounts of its habits seem worth quoting. Grinnell and Storer (1924) write:

The forage range of this warbler lies chiefly in trees other than conifers. Such trees as the black oak and big-leafed maple renew their foliage every spring and the Calaveras Warblers find excellent forage in the insects and larvae which feed upon this tender new leafage during the spring and summer months. Less often these birds may be found in golden oaks and occasionally in Douglas spruces. They usually forage 25 to 40 feet above the ground, keeping within the stratum of new foliage, but they have been seen as low as 10 feet and as high as 70 feet above the earth. When within the foliage their yellow and green coloration makes it difficult to locate them, especially as the birds do not move about as rapidly as some of the other warblers. At times a Calaveras Warbler will poise on rapidly beating wings to capture some insect otherwise out of reach.

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).