The eggs, usually four in number, are of uniform pale blue of a slightly deeper shade than that of the _S. sialis_. They measure .87 of an inch in length by .69 in breadth. Dr. Cooper’s subsequent observations of this species in California enabled him to add to his account of it in his report on the birds of that State. He found it abundant in all the wooded districts, except high in the mountains, and thinks they reside through the summer even in the hot valley of the Rio Grande, where he found them preparing a nest in February. On the coast they are numerous as far north as the 49th parallel. He found a nest under the porch of a dwelling-house at Santa Barbara, showing that, like our Eastern species, they only need a little encouragement to become half domesticated. They raise two broods in a season, the first being hatched early in April. At Santa Cruz he found them even more confiding than the Eastern species, building their nests even in the noisiest streets. One brood came every day during the grape season, at about noon, to pick up grape-skins thrown out by his door, and was delightfully tame, sitting fearlessly within a few feet of the open window. In regard to their song Mr. Ridgway states that he did not hear, even during the pairing season, any note approaching in sweetness, or indeed similar to, the joyous spring warble which justly renders our Eastern Bluebird (_S. sialis_) so universal a favorite. The two Western species of _Sialia_, though associating during the winter in the region along the eastern base of the Sierra Nevada, are seldom seen together during the breeding-season; the _S. arctica_ returning to the higher portions of the thinly wooded desert mountains, while the _S. mexicana_ remains in the lower districts, either among the cottonwoods of the river valleys or among the pines around the foot-hills of the Sierra. Sialia arctica, SWAINS. ROCKY MOUNTAIN BLUEBIRD. _Erythraca (Sialia) arctica_, SWAINS. F. B. A. II, 1831, 209, pl. xxxix. _Sialia arctica_, NUTTALL, Man. II, 1832, 573.—BAIRD, Birds N. Am. 1858, 224; Rev. 64.—SCLATER, Catal. 1861, 11, no. 67.—DRESSER, Ibis, 1865, 478. (Texas, winter, very abundant.)—COOPER, Birds Cal. 1, 29. _Sialia macroptera_, BAIRD, Stansbury’s Rept. 1852, 314 (larger race with longer wings). SP. CHAR. Greenish azure-blue above and below, brightest above; the belly and under tail-coverts white; the latter tinged with blue at the ends. Female showing blue only on the rump, wings, and tail; a white ring round the eye; the lores and sometimes a narrow front whitish; elsewhere replaced by brown. Length, 6.25; wing, 4.36; tail, 3.00. (1875.) _Young._ Male birds are streaked with white, as in _S. sialis_, on the characteristic ground of the adult.