PILEOLATED WARBLERS. Wilsonia pusilla³⁸

Field characters.—Half size of Junco. Top of head with a black cap (restricted in females); plumage plain yellowish green above, yellow on forehead and on under surface of body. No dark streaks or white markings whatsoever. (See pl. 9g). Movements quick and nervous; often flies out to capture passing insects. Voice: Song of male a series of rather flat-toned notes, on about same key, emphasis and intervals between them decreasing toward end of series; call note a similarly flat tchep.

Occurrence.—Common summer visitant, chiefly to Canadian Zone, on west slope of Sierra Nevada (subspecies chryseola). Also found in spring along eastern base of the mountains and as a migrant through the western foothills (subspecies pileolata).³⁸ Lives in thickets over damp ground, usually close to streams, foraging within 6 feet of ground and nesting near or upon the ground. In pairs or solitary.

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³⁸Two subspecies of Pileolated Warbler occur in the Yosemite section. These cannot often be distinguished with certainty in life.

GOLDEN PILEOLATED WARBLER, Wilsonia pusilla chryseola Ridgway, a slightly smaller more yellowish backed subspecies with an orange tinge on the forehead. (See pl. 9g). It nests in California and is a common summer visitant on the west slope of the Sierra Nevada in the Canadian Zone and locally in the Transition Zone. It was recorded sparingly in Yosemite Valley, and commonly from Hazel Green and Chinquapin eastward to Merced Lake.

ALASKA PILEOLATED WARBLER, Wilsonia pusilla pileolata (Pallas), a darker toned more greenish subspecies of slightly larger size which summers in the Rocky Mountain district and the Northwest, was found to be common in spring at Mono Lake and in small numbers as a spring transient near Lagrange.

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In the territory surrounding the Yosemite Valley the small streams and boggy meadows bordered by creek dogwood and willow are frequented by small black-capped yellow birds which are likely to be seen capturing insects close to or within the thickets. The species is the Golden Pileolated Warbler and this territory is its regular headquarters during the summer months. A few of the birds have been seen in summer near the Happy Isles in Yosemite Valley, but the main population at that season is to be looked for in the Canadian Zone above, where pairs are found in favorable country every two hundred yards or so.

The Golden Pileolated Warblers arrive on the west slope of the Yosemite section at least by April 29 (1916). Males seemingly precede the females by a few days. By the middle of May their headquarters are established, and with the coming of June nests are to be expected. After the young are abroad some of the birds wander above the boundary of the breeding zone. Two, for example, were seen on Mount Clark at an altitude of 10,500 feet on August 22, 1915. Our last record of the species for the west slope was made August 28, 1915, when an immature bird was taken at Washburn Lake. The species occurs still later, however, for Mr. Joseph Mailliard (1918, p. 19) states that in 1917 it was noticed up to September 22.

The Alaska Pileolated Warbler is a migrant along both sides of the Yosemite region. Near Mono Lake the first (pileolata) in 1916 was seen on April 29. Thereafter they continued in evidence until May 31, and it is possible that some of the birds remained there to nest. Only a few were noted on the west slope; one of those seen was obtained near Lagrange on May 8, 1919. The time of the return migration of this race has not yet been determined for the Yosemite region. Pileolated warblers (subspecies undetermined) were noted in Yosemite Valley from August 25 until October 4 in 1920 (C. W. Michael, MS).

The Pileolated Warbler, whichever the race, may be known at a glance by the cap of black on the top of the head (pl. 9g). Both males and females, adult and young, have some of this marking. It is largest and most intensely black in adult males. In most warblers the females lack certain of the striking (and to us useful) markings worn by the males, but here the two sexes are closely alike. The present species shows no other contrasting color features; its plumage is yellow, tinged on the back with green. In one of the races (chryseola) the color of the forehead has an orange hue.

Pileolated Warblers do the most of their foraging within 6 feet of the ground and practically never ascend far into trees even to sing. They keep within the cover of the lower stratum of foliage and are therefore only to be caught sight of momentarily. The birds are noted for their habit of darting out after flying insects; indeed one book name of the eastern relative of the pileolated is "black-capped fly-catching warbler." Of all our other warblers only the Tolmie is likely to be found in the same cover inhabited by the Pileolated Warbler. (See fig. 56.) The Tolmie often forages out into the drier chaparral, whereas the present species adheres closely to damp situations, either over boggy ground or else within a few yards of a stream. In favorable country, pairs of Pileolated Warblers may occur as frequently as eight or even more to the linear mile.

The song of the Pileolated Warbler is far less shrill than that of the Yellow Warbler and is less clear and more mechanical than that of several other warblers. The syllables are given all on about the same pitch and about as rapidly as a person can pronounce them, but with the intervals shortening and the emphasis decreasing toward the end of the series: tshup, tshup, tshup-tshup-tshup-tshup. The call note is not nearly so sharp as that of other warblers, but, on occasion, appeals to one as surprisingly loud for the size of the bird. It has an unmistakable quality of its own. Singing is done largely within the cover of the shrubbery; in other words this species does not, as do so many brush dwellers, seek out prominent song perches.

A nest of the Golden Pileolated Warbler was discovered on Indian Creek, below Chinquapin, at about 5800 feet altitude, on June 11, 1915. The nest was discovered through the observer's seeing the female flush as he stepped within a few feet of the site. The bird made off 40 feet or so and then stayed at about that distance, uttering her call note, tchep. The ravine bottom 20 feet away was filled with creek dogwood, Sierran currant, and rank growths of monkey flower and grasses. The slopes adjacent bore incense cedars and sugar pines. The nest was in a depression in an earth bank at the bases of two azalea stems. It was overhung by these stems and also by a mat of dead brakes, which concealed the eggs from view above. The foundation of the nest was of loosely laid dead leaves and this graded into the rest of the structure which was composed of leaves and grass blades. The fine lining was chiefly of deer hair. The structure measured about 3-1/2 inches in diameter outside, and the cavity was 2 inches across and 1-1/4 inches deep. The 5 eggs were fresh.

A family comprising 4 birds was seen near Merced Lake on August 23, 1915. This would suggest a later nesting date than that in the instance just described.