Part 45

HABITS

This subspecies was formerly supposed to range throughout most of Alaska, but its breeding range is now understood to be restricted to the coast region of southern Alaska and British Columbia, from Kodiak Island (the type locality) southward to Vancouver Island. It migrates through California to Mexico and Central America, and probably spends the winter in South America. In El Salvador, according to Dickey and van Rossem (1938), "this race was found only as a fairly common spring migrant through the upper levels of the Arid Lower Tropical. As with D. p. aestiva the winter range undoubtedly lies farther to the south. It is notable that rubiginosa occurs at somewhat higher elevation than the other three forms and was not found at all in the 'tierra caliente.'" This race has been reported in Kansas and in central Texas, but these birds may have been amnicola, which somewhat resembles rubiginosa and which had not been accepted at that time.

Ridgway (1902) describes the Alaska yellow warbler as "similar to D. ae. aestiva, but slightly smaller and much duller in color. Adult male darker and duller olive-green above, the pileum concolor with the back or else becoming slightly more yellowish on forehead (very rarely distinctly yellowish on forehead and fore part of crown); wing-edgings less conspicuous, mostly yellowish olive-green, sometimes inclining to yellow on greater coverts. Adult female darker and duller olive-greenish above, duller yellow below." He might have added that the chestnut streaks on the breast are narrower than in aestiva.

Nothing seems to have been published on the nest and eggs of the Alaska yellow warbler, nor on its habits, all of which probably do not differ materially from those of the species elsewhere in similar environment.

DENDROICA PETECHIA MORCOMI (Coale)

ROCKY MOUNTAIN YELLOW WARBLER

HABITS

This is another race that was described many years ago by H. K. Coale (1887) but has only recently been accepted by the A. O. U. Coale gave it its scientific name in honor of J. Frean Morcom and called it the western yellow warbler. The following remarks by Dickey and van Rossem (1938) tell the story very well:

The race of yellow warbler summering in the Great Basin and Rocky Mountain regions of the United States of late years has been generally overlooked and has been synonymized commonly with aestiva or, in part, with brewsteri. Although not a well differentiated form, its characters are readily apparent in series, and there is no reason why it should not be accorded equal standing with the races currently recognized. The underparts of the males are heavily marked, and in this respect morcomi is not distinguishable from aestiva. Dorsally, however, morcomi is darker and less yellowish green, particularly on the interscapular region. The females are, age for age, more buffy (less yellowish) below and darker and more grayish above than the females of aestiva. In comparison with brewsteri, morcomi (particularly the bill) is larger, and the males are more heavily streaked below. The range of morcomi is the Rocky Mountain region of the United States, north to Wyoming and Idaho, west to the eastern slope of the Sierra Nevada, and south (in the western part of its range) to Mammoth, Mono County, California. We have not seen material from the southern Rocky Mountains; so we cannot state the southern limits in that region.

They call it a "common spring and fall migrant and winter visitant in the lowlands," of El Salvador. "Dates of arrival and departure are August 1 and April 9."

Angus M. Woodbury has sent me a copy of the manuscript for "The Birds of Utah," by Woodbury, Cottam, and Sugden, from which I infer that the haunts, nesting, and other habits of the "western yellow warbler," as they call it, do not differ materially from those of the well-known eastern bird. They say of its status in Utah: "This yellow warbler is a common summer resident from early May to late August, the vanguard sometimes reaching here in late April and stragglers sometimes lingering into September, the latest record being September 23. It is primarily a bird of the riparian growths along water edges, either of streams, ponds or lakes or irrigated areas, particularly of the valleys and lower canyons, but occurs higher in the canyons in suitable habitat up to at least 8,000 or 9,000 feet. It does not seem to be attracted to large trees such as cottonwoods, but seems to prefer the more leafy shrubbery and small trees of developmental stages in ecological succession. In migration, it sometimes leaves this niche and may occasionally be found elsewhere. * * *

"In nesting, it is usually found in a bush, chaparral or small tree stratum, seldom going to the ground or to the tops of trees. Its nests are compactly woven cups generally placed from 3 to 10 feet above ground, sometimes 15 feet, in rosebushes, willows, choke cherries, hawk-berries, oaks, young cottonwood or boxelder trees, usually within a short distance of the water's edge. The nest is usually composed of gray plant fibers, bark shreds or grasses and is usually lined with some downy substance such as cottonwood or willow cotton or hair."

DENDROICA PETECHIA BREWSTERI Grinnell

CALIFORNIA YELLOW WARBLER

HABITS

The 1931 A. O. U. Check-List gives the breeding range of this subspecies as the "Pacific coast strip from western Washington south through Oregon and California, west of the Great Basin and southeastern deserts to about lat. 30° in Lower California." It intergrades with rubiginosa on the north and with morcomi to the eastward, but exact boundaries are difficult to define. It seems to range well up into the mountains, for James B. Dixon tells me that he has found it nesting in Mono County, Calif., at altitudes of 6,500 to 9,200 feet.

Dr. Joseph Grinnell (1903) in an interesting study of western yellow warblers, bestowed the above name on the California bird, for which he gives the following subspecific characters: "Resembling Dendroica aestiva aestiva, from which it differs in smaller size, paler (or less brightly yellow) coloration, and, in the male, narrower streaking on under surface; differs from Dendroica aestiva rubiginosa in much smaller size and yellower coloration, and from Dendroica aestiva sonorana in smaller size and much darker coloration."

Spring.--Both rubiginosa and brewsteri occur in California and in Washington on migrations. As it is difficult to distinguish the two forms in life, some of the following remarks may refer to either or both of these two subspecies. Mrs. Amelia S. Allen writes to me that this species "is the latest of the warblers to arrive in the San Francisco Bay region for the breeding season. Sometimes they are here by April 8, but the average date is about April 18. At Lake Tahoe, the first week of June, breeding pairs were settled in the willows and migrants on their way farther north were migrating through."

Samuel F. Rathbun says in his Washington notes: "Our experience with this species, based on many years of observation, is that the birds in the spring migration progress northward in a series of what may be called waves. Invariably the first noted will be one or two individuals, and these are heard for a short time only and evidently move on. Then there is a break of a day or so before the next are heard, a larger number. A period of a day, or perhaps two or three, may again elapse before the main body of birds arrive and they are heard on all sides. Common in and about the city at this period, it haunts the shade trees lining the streets and the fruit trees in the gardens, but is not at all partial to the outlying sections, except in the more cultivated areas and the orchards. It is essentially a bird of the older settled districts, wherever fruit trees and deciduous trees may abound."

For May 6, 1924, he remarks, "These warblers drifted by all day, in ones and twos or threes, straggling, but, although seemingly widely separated, always within hearing distance of each other. At times there will be a break when apparently none are passing, then in the distance the song will be heard again, soon growing louder, as the bird draws nearer, following in the wake of others that have preceded him, his song in turn growing fainter in the distance after he has passed."

Nesting.--The summer haunts and nesting habits of the California yellow warbler are generally similar to those of the eastern bird. Grinnell and Storer (1924) write:

Yellow warblers nest abundantly on the floor of Yosemite Valley. Some of the nests are in growths close to water, whereas others are located in brush tangles or other rank growths back some distance from the streams. A nest found June 7, 1915, may be taken as fairly typical. It was 52 inches above the ground in the crotch of a forking stem of a chokecherry which grew in a clump of the same plant, and was shaded by a black oak. As usual it was higher than wide outside, being 3-1/2 inches in height by 3 to 3-1/4 inches in diameter. The cuplike cavity was 1-3/4 inches across at the top and the same in depth at the center. Shreds of bark and flat plant fibers were the principal materials used in construction, the lining being of horsehair and a few feathers.

One nest was "4 feet above the ground in a mountain lilac (Ceanothus integerrimus)," and another "was placed about 15 feet above the ground in a small pine tree growing at the margin of a pond. It rested on the next to the topmost whorl of branches and one side was against the slender trunk of the tree."

In the Lassen Peak region, Grinnell, Dixon, and Linsdale (1930) report four nests in willows, one in a wax-berry (Symphoricarpos), one in a snowbush, and one fastened between stems of rose and willow at the edge of a clump of rose.

Eggs.--Three or four eggs seem to constitute the commonest set for the California yellow warbler. These are hardly distinguishable from those of the eastern bird, though they average, perhaps, more heavily marked. The measurements of 40 eggs average 16.6 by 12.4 millimeters; the eggs showing the four extremes measure =18.3= by 13.5, 17.8 by =15.0=, =14.7= by 12.2, and 16.3 by =11.4= (Harris).

Food.--Prof. F. E. L. Beal (1907) analyzed the contents of 98 stomachs of California yellow warblers, and found that the animal matter amounts to 97 percent of the food, consisting wholly of insects and a few spiders.

The largest item is Hymenoptera, which amounts to over 30 percent, almost half of which are ants. The remainder are small bees and wasps, some of which are probably parasitic species, though none were positively identified. * * * Caterpillars, with a few moths, aggregate over 18 percent.

Beetles form nearly 16 percent of the diet, and embrace about a dozen families, of which the only useful one is that of the ladybirds (Coccinellidae), which are eaten to a small extent. The great bulk of the beetle food consists of small leaf-beetles (Chrysomelidae), with some weevils and several others. One stomach contained the remains of 52 specimens of Notoxus alamedae, a small beetle living on trees. Bugs (Hemiptera) constitute over 19 percent of the food, and are eaten regularly every month. Most of them consist of leaf-hoppers (Jassidae) and other active forms, but the black olive scale appeared in a number of stomachs. Plant-lice were not positively identified, but some stomachs contained a pasty mass, which was probably made up of these insects in an advanced stage of digestion.