This species typically prefers more wooded breeding habitats than does the mountain bluebird, though co-occurs widely with it. Polytypic. Length 7".
The western bluebird is shorter-winged and shorter-tailed than the mountain bluebird, producing similar wing/tail ratio, and different primary projection/tertial length ratio. Male: rich blue on head (including chin and throat), wings, and tail. Female: grayer head and back; paler orange underneath; at least partial whitish eye ring. Juvenile: similar to the eastern bluebird, being strongly spotted dark on underparts, whitish on upperparts and wing coverts, but with tertials fringed grayish; immatures distinguishable by browner primary coverts, duller upperparts. Flight is level and typical of thrushes. Migrates diurnally in flocks, occasionally with mountain bluebirds, from which they can be distinguished by more obvious pale underwing stripe (created by darker wing linings and flight feathers) and, with experience, by shorter, rounder wings.
Six subspecies, 3 in North America; Eastern bairdi (breeds western to central Utah, southern Arizona) larger; more extensive chestnut on upperparts than western occidentalis; jacoti of southeastern New Mexico and trans-Pecos Texas smallish, with extensive dark chestnut on upperparts.
Unlike plumage of the eastern bluebird, male’s head entirely blue; females confused with other bluebird species.
Call: similar to other bluebirds, but a more single-noted and harder few, though some calls are fairly strongly 2-noted; this call also given in flight. Song: consists of a series of call notes and is primarily heard at dawn.
Status and Distribution
Uncommon to fairly common at mid- and low elevations in western lower 48, extending north into Canada in British Columbia. Breeding: nests in parklike, low-elevation pine and mixed forests, rich riparian bottomlands, and oak savanna. Migration: short-distance migrant that rarely strays far from nesting areas. Spring arrival central Colorado ±15 March; eastern Washington ±10 April. Fall: most depart southern British Columbia ±31 October; northern Colorado ±30 September. Winter: primarily in southwestern United States and northern Mexico, but range to southern Washington on Pacific slope; northern extent of wintering variable, dependent on food (juniper or mistletoe berries). Vagrant: casual east to North Dakota, western Kansas, and eastern Texas.
Populations depressed by alteration of pine habitats due to fire suppression.
—From the National Geographic book Complete Birds of North America, 2006