COWBIRDS. Molothrus ater (Boddaert)²²

Field characters.—Slightly smaller than female Red-winged Blackbird, bill short and thick, sparrow-like. Male with head and chest dull brown, plumage otherwise black with a slight iridescence; female entirely dull brown, paler on under surface where faintly streaked; no contrasted color markings in either sex. General habits of a blackbird. Voice: So far as heard by us, a protracted squeal or high-pitched whistle, uttered by male.

Occurrence.—Found as a summer visitant in the Lower Sonoran Zone at Snelling and near Lagrange (race obscurus); also east of the Sierras, in the Transition Zone in the vicinity of Mono Lake (race artemisiae). One individual of the latter race was picked up dead 3 miles north of Mount Bullion on December 27, 1917. Frequents stream-side willow thickets and also stock corrals and pastures.

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²²Two species of Cowbirds are found in the Yosemite region. At Snelling and Lagrange is found the Dwarf Cowbird, Molothrus ater obscurus (Gmelin), while east of the mountains in the vicinity of Mono Lake there is the Nevada Cowbird, Molothrus ater artemisiae Grinnell. These two races differ chiefly in size, the former being smaller throughout; but these differences can be determined only from specimens in hand.

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Our first record of the Cowbird in the Yosemite section was made on May 29, 1915, when a male of the Dwarf race was obtained at Snelling after attention had been attracted by its high-pitched squeal. This bird was perched at the tip of a tall dead tree standing within the dense growth of willows bordering the Merced River. A pair of Dwarf Cowbirds was seen near the Tuolumne River, 2 miles below Lagrange, on May 8, 1919, but no evidence as to their breeding activities was obtained, nor did we chance to find Cowbirds' eggs in any of the birds' nests examined there.

At Mono Lake in the season of 1916 a number of Nevada Cowbirds were obtained. Two birds taken on May 10 showed little sign of breeding activity, but a female obtained May 23 contained an egg nearly formed which probably would have found its way into the nest of some small bird the following morning. It is to be recalled here that the female Cowbird is a shirker in that she deposits her eggs, singly, in the nests of other birds, usually species smaller than herself. She thus foists upon these other birds the duties of incubating her eggs and rearing her off spring. On May 31 a second female was taken which contained a good-sized yolk. Another bird taken the same day was a non-breeder, possibly having failed to find a mate. On June 17 a third female was taken which gave indications of laying activity close to the time of capture. Cowbirds were heard in the corrals at the Farrington Ranch near Williams Butte on September 14, 1915, but since none was obtained nor any others observed during the subsequent week when intensive field work was carried on in the vicinity, this may have marked the last appearance of the species in the region for that season.