any of the three species of the North American genus Sialia of the chat-thrush group (family Turdidae, order Passeriformes). The eastern bluebird (S. sialis), 14 cm (5 ¹/₂ inches) long, and the western bluebird (S. mexicana) are red-breasted forms found east and west of the Rockies, respectively; the mountain bluebird (S. currucoides), also of the west, is all blue. Bluebirds arrive from the south in earliest spring, uttering soft, blurry notes. They live in open country and woodland glades; they nest in holes in trees or in fenceposts—and in bird boxes, if they are not driven away by starlings or house sparrows.