bluebird common name for a North American migratory bird of the family Turdidae (thrush family). The eastern bluebird, Sialia sialis, is among the first spring arrivals in the North. It is about 7 in. (17.8 cm) long. The plumage of the male appears vivid blue in bright light and black at a distance; the breast is cinnamon-red, the under parts white. The female's coloring is duller. The bluebird usually nests in orchards or on the edges of woodlands but will also use nesting boxes. As a destroyer of insects it is of great value; it also eats wild fruits. Related birds are the mountain, the western (genus Sialia ) or chestnut-backed, and the Florida bluebirds. Bluebirds have a cheerful call and a sweet, warbling song. They raise several broods during a single mating season. The female is responsible for the incubation duties. Bluebirds are classified in the phylum Chordata , subphylum Vertebrata, class Aves, order Passeriformes, family Turdidae.