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.”