blackbird, common name in North America of a perching bird allied to the bobolink, the meadow lark, the oriole, and the grackle and belonging to the family Icteridae. The European blackbird, Turdus merula, is a thrush. The blackbird is possibly the most numerous N America land bird. The red-winged blackbird of E North America is a familiar sight, its scarlet shoulder patches conspicuous among the tall grasses of the marshes and wet meadows where it nests. It eats grain, insects, and weed seeds. Another common species is the yellow-headed blackbird, Xanthocephalus xanthocephalus. Except during the breeding season, blackbirds usually travel in flocks. The yellow-headed, the tricolored red-winged, and brewer blackbirds are found in the West. The rusty blackbird, glossy blue-black in summer when the brown edging of its winter feathers has worn off, winters in the United States. Many members of the family are polygamous, although the incidence of polygamous behavior varies from population to population. For example, in the brewer blackbird, the male becomes polygamous only when there are more females than males; when the balance is even, monogamy is the rule. The female blackbird usually builds the nest, which consists of a cup-shaped structure made of grasses. Flocks of blackbirds may be as large as 5 million birds, and they often do serious crop damage when foraging for food. However, the birds are invaluable because of the insects they consume. Blackbirds are classified in the phylum Chordata, subphylum Vertebrata, class Aves, order Passeriformes, family Icteridae.