Sialia mexicana

Adult male has a bright blue head and upperparts (may have some reddish coloration), chestnut breast (chestnut coloration may be bisected by blue) and scapulars (shoulder patches), and blue-gray belly and undertail coverts. Adult females are considerably duller and not extensively bluish. The head and throat are gray, the back is gray-brown, the abdomen and undertail coverts are grayish, and there is blue in the wings and tail. Adult plumages do not change much throughout the year. First-year birds resemble adults but are slightly duller. Juveniles have a white eye-ring and are gray-brown above, streaked or spotted with white; the breast is heavily streaked, and the wings and tail have some blue coloration. Length is around 7 inches (18 cm).

Breeding range includes western North America from southern British Columbia and southwestern Alberta south to northern Baja California and the Central Volcanic Belt of Mexico, excluding most of the Great Basin. Breeding range in the United States extends east to Wyoming, Colorado, New Mexico, and western Texas. Winter range includes the breeding range (typically at lower elevations) in southern British Columbia, western Oregon, California, Baja California, southwestern Nevada, and from central Utah and portions of central Colorado and New Mexico south. Western bluebirds also winter in areas outside the breeding range in California, Baja California, Arizona, New Mexico, westernmost Texas, and throughout much of northern Mexico.

Habitat includes open woodlands, farmlands, orchards, savanna, and riparian woodlands; also deserts in winter. Nests are in natural tree cavities, abandoned woodpecker holes, or bird nest-boxes, usually 5-40 feet (1.5-12 meters) above ground.

Nesting may begin in March in some areas (usually in April-May in most areas), and may extend into July or August. Clutch size is 2-6 (typically 5). Most females produce or attempt two broods per year. Incubation lasts 12-18 days. Altricial nestlings are tended by both parents. Fledged young are tended by the male if the female re-nests. Western bluebirds may wander/withdraw from northern breeding areas during the winter. Some move to higher elevations in fall.