Blue-bird, any bird of the American genus Sialis. The species, named from the general colour of their plumage, are about the size of robins, and are as great favourites with the Americans as robins are in Britain. The adult male of S. sialis, the Eastern blue-bird, from the eastern States of North America, is rather more than 6 in. long; azure blue above, reddish brown beneath, belly and under tail-coverts white. S. mexicana, the Californian blue-bird, ranging from the Rocky Mountains to the Pacific, is slightly smaller, bright azure blue above, with more or less chestnut on the back, sides dark reddish-brown, rest of under-surface pale bluish. S. artica, the Rocky Mountain blue-bird, is the smallest species; greenish-azure with white belly. The females are duller in colour than the males; the young are spotted and streaked with white. These birds feed on small beetles and the larvae of the smaller butterflies and moths.