BLACK-THROATED GRAY WARBLER. Dendroica nigrescens (Townsend)

Field characters.—Half bulk of Junco. Head, chin, and throat black (mixed with white in female and young), with a white line backward over eye and another from bill down side of throat; sides of body streaked with black; rest of under surface white; upper surface bluish gray; two light bars on wing; tail white margined. No conspicuous yellow in plumage. (See pl. 9f). Movements rather deliberate for a warbler. Voice: Song of male a slow drawling wee'-zy, wee'-zy, wee'zy, wer; call note a low chit.

Occurrence.—Moderately common summer visitant locally in Transition Zone on west slope of Sierra Nevada. Recorded from 3 miles east of Coulterville eastward to Yosemite Valley. Seen in fall migration near Mono Lake. In nesting time practically restricted to golden oaks. Solitary or in scattering parties.

The Black-throated Gray Warbler is a bird of the golden oaks and is to be found in fair numbers in the heavy growths of these trees which clothe the talus slopes along the north and south walls of Yosemite Valley. Elsewhere in the Yosemite section the species was found only in stands of this same oak or in nearby situations. This warbler is therefore notable for being one of the very few birds which, in the Yosemite section, is entirely restricted to the Transition Zone. The Yosemite Falls Trail below Yosemite Point, the Glacier Point short trail below Union Point, the Big Oak Flat road below Gentrys, and the Little Yosemite trail below Nevada Falls are good places from which to study this warbler, for all these trails pass through golden oaks.

This bird is preeminently a black and white warbler. (See pl. 9f). At a distance no yellow shows (though a small spot of this color is present in front of the eye). In this feature the bird departs from the color scheme of its local relatives, all of which show, even at a distance, more or less yellow. In the adult male of the present species the head, chin, and throat are chiefly black. The female has less black, her chin often being mixed black and white; this is true also of the young. Adults and immatures of both sexes share in common the white stripe above and behind the eye, the white line from bill down side of throat, the two light wing bars, the white margined tail and, best of all, the black streaking on the sides of the otherwise pure white under surface. The back is bluish gray in all.

A striking similarity in markings exists between the Townsend and the Black-throated Gray warblers. One is an exact replica of the other save that the yellow of the former is replaced by white in the latter. This parallelism extends to all ages and both sexes. The Townsend Warbler is only a transient here.

The Black-throated Gray Warbler arrives in the Yosemite region by April; it was already present in Yosemite Valley on April 29, 1916. It continues here until early fall, several being seen in company with some Audubon Warblers, along the Glacier Point trail, on September 25, 1915. The latest seasonal occurrence known is of a single bird recorded near Feliciana Mountain southwest of El Portal, on October 30, 1915. East of the mountains near Williams Butte two of these warblers, doubtless migrants, were seen in a mountain mahogany bush on September 16, 1915.

The population of this bird seems to fluctuate markedly from year to year. During a 50-minute walk up the Yosemite Falls trail to Columbia Point on June 4, 1915, 14 of these birds were recorded. A similar climb, through the somewhat lighter growth on the Sierra Point trail, May 16, 1919, revealed only one singing male, and elsewhere in the Valley, in the latter year, the numbers of this species were unusually small.

The Black-throated Gray Warbler is not a particularly active species and its slow movements combined with a 'disruptive' pattern of coloration sometimes render it difficult to see against the sunlit foliage of the oaks. The bird inhabits largely the crown and middle foliage and so does not often come into plain view. The song of the Black-throated Gray Warbler is a rather lazy, drawling utterance, deep-toned rather than shrill. Wee-zy, wee-zy, wee-zy, wee-zy-weet; tsewey, tsewey, tsewey, tsewey-tsew; zuee, zuee, zuee, soop; si-si-weezy, weezy we-tsu'; oweze-weze-weze-weze-chur, are syllabifications written by us at different times when individual birds were singing close at hand. There are modifications in the song; sometimes the terminal syllable is omitted and again only three of the two-syllabled notes are given. The ordinary call is a rather low, one-syllabled chit.

Near Smith Creek, east of Coulterville, a nest of the Black-throated Gray Warbler was seen on June 5, 1915. It was placed 5 feet 6 inches above ground in a mountain lilac (Ceanothus integerrimus) bush against a main stem. Outside, the nest measured 2-1/4 inches both in diameter and height. There were 4 young birds only 2 or 3 days old. Upon our approach the female flushed and made off, with the broken-wing ruse common to so many species. Then she perched on a nearby limb and fluttered her wings, chiting every second or so in remonstrance at our intrusion.

The same day, in the forest on the hill above and immediately east of Coulterville, one of our party interrupted an attack by a California Striped Racer upon a brood of Black-throated Gray Warblers. The female parent was much excited, flying from twig to twig, calling, and fluttering her wings. Near by, on the ground, was one of the young warblers. There was good evidence that the snake had already swallowed another member of the brood.

The records of two broods given in the preceding paragraphs indicate that the beginning of nesting was, in one case at least, close to the first of May. A pair of these birds intent upon nesting duties was seen in the oaks near Yosemite Falls on May 23, 1919; their nest, however, was not seen. A family group, with the young birds out of the nest and uttering food calls, was observed in the Valley on July 27, 1915. Nesting is probably mostly over by mid-July, as the song season ends about the first of that month.