Part 60

In the Atlin region of northern British Columbia, according to Mr. Swarth (1926), it is a common species, breeding mostly in the lowlands:

A nest with five fresh eggs (Mus. Vert. Zool. no. 1992) was taken by Brooks on June 15. It was in a slender spruce, one of a small thicket in a locality that is largely poplar grown, about forty feet from the ground and near the top of the tree. It rested on the twigs forming the terminal forks of a branch, about three feet from the trunk. The outer walls of the nest were built mostly of the shredded bark of the fire-weed stalks, with a little fire-weed 'cotton,' some coarse grass and small twigs, and several wing and tail feathers of a small bird. In the lining there was some horse hair, mountain sheep hair and a few soft feathers.

Another nest, containing newly hatched young on June 28, was in a small jack pine in open woods on the shore of Lake Atlin.

During the last week in August and the first week in September the southward exodus was at its height. Flocks of warblers, mostly this species, flitted rapidly through the poplar woods, and there was a constant stream of myrtle warblers making long flights overhead. The last one, a single bird, was seen September 19.

As the breeding ranges of Hoover's warbler and Audubon's warbler approach each other in British Columbia and may even overlap it would not be strange if hybrids between these two closely related species should occasionally turn up. Joseph Mailliard (1937) calls attention to a number of such hybrids between both forms of coronata and auduboni. And more recently, Fred M. Packard writes to me: "I have inspected skins in most of the major museums in America to detect these hybrids, and have been surprised at the number I have found. All but two were taken in the Rockies or farther west, so that presumably the subspecies concerned is D. c. hooveri."

DENDROICA AUDUBONI AUDUBONI (Townsend)

PACIFIC AUDUBON'S WARBLER

PLATE 34

HABITS

The Pacific Audubon's warbler is a handsome western species closely related to our familiar myrtle warbler, which to a large extent it replaces, and is much like it in behavior and appearance; but it has one more touch of color in its brilliant yellow throat, five spots of yellow instead of four, and it has more white in the wings and tail. Although its breeding range does not extend nearly as far north as that of the myrtle warbler, it extends farther south, and to considerably higher altitudes, breeding largely in the Canadian Zone among the pines, firs, and spruces. Including the range of the Rocky Mountain form (memorabilis), which has not yet been admitted to the A. O. U. Check-List, the type race breeds from central British Columbia, central Alberta, and west-central Saskatchewan southward to southern California, northern Arizona, New Mexico, and western Texas. Throughout most of this range it is widely distributed in the lowlands only during the winter, retiring to the mountains for the breeding season.

In the mountains of New Mexico it has been found breeding at altitudes of from 7,500 feet to over 11,000 feet. In Colorado it breeds at similar elevations and perhaps up to nearly 12,000 feet. In southern California, Dr. Joseph Grinnell (1908) found it breeding in the San Bernardino Mountains from 9,000 feet "almost to timber limit, 10,500 feet elevation, at least. * * * This was one of the most abundant birds of the San Bernardino mountains, and was widely distributed from the lower edge of the Transition zone up through the Boreal." Grinnell and Storer (1924) write:

The Audubon Warbler is the most widely distributed and the most abundant of all the species of wood warblers found in the Yosemite region. It occurs in numbers throughout the main forested districts of the mountains during the summer season, and it frequents the deciduous trees and brush of the foothill and valley country in the winter time.

Altitudinally its summer range extends from the beginning of the Transition Zone yellow pines on the west slope, at 3300 to 3500 feet, up through the lodgepole pines and other conifers of the Canadian and Hudsonian zones to the upper limit of unstunted trees at 10,000 feet or a little higher. * * *

During the summer season the Audubon Warbler keeps mainly to coniferous trees, foraging from 10 to 50 feet or more above the ground. In the Transition Zone and part of the Canadian Zone it shares this habitat with the Hermit Warbler, but at the higher altitudes it is the only warbler present in the evergreen forest.

Farther north, in Mono County, Calif., James B. Dixon tells me that he found it nesting between 7,600 and 9,500 feet elevation. Referring to the Toyabe region in Nevada, Dr. Jean M. Linsdale (1938) found the Rocky Mountain form in a somewhat different environment: "In the mountains the area occupied by this warbler agreed fairly well with the area covered with trees. Individuals were seen most often in aspens, limber pines, birches, willows, and mountain mahoganies." Angus M. Woodbury (MS.) says of the breeding range of the Rocky Mountain form in Utah: "It summers in altitudes ranging from about 7,000 to 10,000 feet and nests in almost any of the components of the forests in those altitudes; pine, fir, spruce, aspen, or oak."

In Washington, Audubon's warbler is common and well distributed from near sea level in the vicinity of Seattle and Tacoma up to about 8,000 feet in the mountains. Near Tacoma, D. E. Brown showed us some typical lowland haunts of this warbler in the so-called "prairie region." On this smooth, flat land, a fine growth of firs and cedars was scattered about in the open; the two or three local species of firs were most abundant and were growing to perfection, being well branched down to the ground.

Spring.--There is a northward as well as an altitudinal migration in the spring. Samuel F. Rathbun says in his notes from Seattle: "Although the Audubon's is of frequent if not regular occurrence during the winter, a migration of the bird through the region is to be noted each spring and fall." Near Seattle the first birds are seen and their song is heard about March 10 to 15, and numbers are seen passing through up to the latter part of April. "By way of comparison, in the Lake Crescent section the first are seen about April 2, at the earliest, and after three weeks the last appear to have passed by, as the species performs its spring migration in a leisurely manner." A later wave of migrants passes through Seattle between April 10 and 25, probably birds that nest farther north.

Migration is evident in Utah, for Woodbury (MS.) says: "In addition to its summer residence, it is a common migrant through the state, and a sparse winter resident, mainly at low altitudes. It migrates through the streamside and cultivated trees of the valleys, including shade trees and orchards. The migrations cover a period of about 6 weeks each in spring and fall, usually from about mid-April to the end of May and from mid-September to the end of October, but in different years the waves may be a little earlier or later."

In California, there is a gradual exodus of Audubon's warblers from the lowlands to the mountains during April and May. Mrs. Amelia S. Allen tells me that "by the end of April they have disappeared from the San Francisco Bay region." And Swarth (1926b) says that in May, following the spring molt, "there is a gradual withdrawal of the birds to the higher mountains and to more northern latitudes."

Audubon's warbler occurs abundantly on the Huachuca Mountains, Ariz., but as a migrant only, during March, April, and May. Swarth (1904) writes:

Though distributed over all parts of the mountains, they were at all times more abundant in the higher pine region, than elsewhere; and on April 24, 1903, I found them particularly numerous along the divide of the mountains, evidently migrating. They could hardly be said to be in flocks on this occasion, for along the ridge, which runs almost due north and south, there was for several miles a continuous stream of Audubon Warblers travelling rapidly from tree to tree, always moving in a northerly direction; sometimes a dozen or more in one pine, and sometimes only two or three, but never stopping long and all moving in the same direction. Almost all that were seen on this occasion were high plumaged males, hardly half a dozen females being observed for the day.

This was about two weeks before the local breeding race (D. a. nigrifrons) might be expected to arrive.

Dr. Merrill (1888), at Fort Klamath, Oreg., found Audubon's warblers "extremely abundant during the migrations. A few males were seen at Modoc Point on the 8th and 9th of April, and at the Fort on the 15th; by the 20th they were quite plentiful. A second 'wave' composed of both males and females, which latter had not previously been seen, arrived about the 4th of May, when they suddenly became more abundant than ever, bringing D. aestiva morcomi and H. lutescens with them."

Nesting.--The only two nests of Audubon's warbler that I have seen were shown to me in Washington, near the State University at Seattle. The University is located on high land at the north end of Lake Washington, where the steep banks, sloping down to the lake, are heavily wooded with a mixed growth of large and small firs of at least two species, as well as cedars, alder trees, and maples. In the more open part of the woods I was shown, on April 29, 1911, a nest of this warbler placed about 30 feet from the ground on two small branches and against the trunk of a tall Douglas fir beside a woodland path. The other nest I saw in the previously described "prairie region" near Tacoma on May 14, 1911; it was placed only 9 feet from the ground but 10 feet out from the trunk of a dense Douglas fir growing in the open, and was well concealed in the thick foliage.

These nests were evidently typical for the region, according to Rathbun. He mentions in his notes two other nests. One, found May 2, 1909, on the east side of Lake Washington and along a road, was 30 feet from the ground in a small hemlock, near the extremity of one of the limbs and 7 feet out from the trunk. The other, found May 11, 1913, was in a small fir about 30 feet up and about 4 feet from the trunk on one of the lower limbs. "The nest is a very beautiful structure, constructed outwardly of very small twigs from the fir or hemlock, inside of which are placed smaller ones of the same character, with black rootlets, and lined with feathers, of which a quantity are used, and a few horsehairs. It is a compactly built affair." Dawson and Bowles (1909) say that the nests are placed from 40 to 50 feet up, and usually measure 4 inches in width outside by 2-3/4 in depth; and inside 2 by 1-1/2 inches. They are made externally of such materials as fir twigs, weed tops, flower pedicels, rootlets, and catkins, and are heavily lined with feathers of various birds--including grouse, ptarmigan or domestic fowls--these feathers often curving upward and inward so as partially to conceal the eggs.

Dr. J. C. Merrill (1898) found a very different type of nesting near Fort Sherman, Idaho: "Here a majority of the nests I found were in deciduous trees and bushes, generally but a few feet from the ground. One was in a small rose bush growing at the edge of a cut bank overhanging a road where wagons daily passed close to it. * * * Occasionally one was seen in deep woods by the roadside near where hay had been brushed off a load on a passing wagon; this was utilized for the entire nest except lining, making a conspicuous yellow object in the dark green fir or pine in which it was placed."

P. M. Silloway (1901) found a nest of Audubon's warbler near Flathead Lake, Mont., that was 18 feet from the ground in a fork of a willow. "The fork containing the nest was in a main stem, upright, a number of feet below the leaf-bearing part of the tree, so that the nest was exposed quite fairly to view." H. D. Minot (1880) found one at Seven Lakes, Colo., in an odd situation: "The nest, composed of shreds and feathers, with a few twigs without and hairs within, was built in a dead, bare spruce, about twenty feet from the ground, compressed between the trunk and a piece of bark that was attached beneath and upheld above, where a bough ran through a knot-hole, so compressed that the hollow measures 2-1/4 x 1-3/4, and 1-1/2 inches deep." Dr. Chapman (1907) describes a nest from Estes Park, Colo., as "loosely constructed of weed-stems and tops, and strips of bark, lined with fine weeds and horse-hair."

Mr. Woodbury (MS.) describes Utah nests as "compactly woven, cup-shaped structures, usually of fine grasses, plant fibers or shredded bark, lined with feathers or some substitute, and camouflaged with some fine stringy material holding bracts or other small particles in place." He reports nests in such conifers as spruce, balsam, and ponderosa pine, and in aspen and oak.