Sialia mexicana

Adult male has a bright blue head and upperparts (may have some reddish coloration), chestnut breast (chestnut coloration may be bisectedby 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).

See Kaufman (1992) for detailed information on identification of bluebirds.

Habitat includes open woodlands, farmlands, orchards, savanna, riparian woodlands, and burned 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.

In montane forests in Colorado, Winternitz found an average of 0.6 breeding bluebirds/ha (Bureau of Land Management, no date). Territories averaged 0.43 hectares (Balda 1967) and 0.56 hectares (Szaro 1976) in two Arizona studies. Gopher snakes are common nestbox predators in central coastal California (Eichholz and Koenig 1992).

The distribution and abundance of this species is limited by nest site availability. For example, in northern Arizona, density increased from 9-21 breeding pairs per 100 acres to 65 pairs per 100 acres after nest boxes were added to the habitat (Brawn and Balda 1988).

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 3-8 (typically 4-6). Most females produce or attempt two broods per year. Incubation lasts 13-14 days. Altricial nestlings are tended by both parents. Fledged young are tended by the male if the female re-nests.