About the Eastern Bluebird
The eastern bluebird is a species familiar to millions in eastern North America. Polytypic. Length 7" (17.5 cm).
Male: bright blue above, with orange throat, ear surround, chest, sides, and flanks. Female: differs in that upperparts are less blue (often grayish); has partial whitish eye ring, and whitish throat bordered by brown lateral throat stripes. Juvenile: very similar to western bluebird, but with tertials fringed cinnamon; immatures discernable with duller upperparts and browner primary coverts. Flight as in other bluebirds; pale wing stripe less obvious than in the western bluebird.
Four subspecies in North America; compared with widespread and somewhat migratory, short-billed nominate sialis, resident fulva of southern Arizona slightly larger and paler, males with cinnamon-fringed scapulars; southern Texas nidificans larger, more richly colored, with upperparts feathers edged with cinnamon; and southern Florida grata with longer bill.
Male western bluebird with all-blue head, including chin and throat, and generally a deeper blue. Male western also has at least some rufous on upperparts, particularly on scapulars.
Call: musical, typically 2-noted too-lee. This call is also given in flight. Song: mellow series of warbled phrases; varied.
Status and Distribution
Common in the eastern three-fifths of the lower 48 states and in southern Canada; uncommon and local in southeastern Arizona. Breeding: nests in open woodland, second-growth habitats, and along the edges of fields and pastures, placing nest in cavity; readily accepts nest boxes. Migration: short- to medium-distance migrant. Spring: arrivals. Great Lakes ±25 February; southern Saskatchewan ±1 April. Departs northernmost range during October. Usually migrates in flocks. Winter: almost always in flocks, often mixed with yellow-rumped, pine, and palm warblers and/or dark-eyed juncos; mainly central and southern United States., but to south-central Colorado, central New Mexico, and northeastern Mexico. Vagrant: casual west to Alberta and Utah; recent local colonization in western Colorado.
Nest boxes have apparently helped reverse a decline.
—From the National Geographic book Complete Birds of North America, 2006