Marsh blackbirds that may outnumber every other land bird
Red-winged blackbirds (Agelaius phoeniceus) breed from Alaska through much of North and Central America. Winter censuses sometimes find loose flocks so huge that writers call them the continent's most abundant land bird. Linnaeus named the species in 1766; it is sister to Cuba's red-shouldered blackbird.
This icterid breeds from Alaska and Newfoundland down to Florida, Mexico and Guatemala, with outlying pockets in El Salvador, Honduras and Costa Rica. A few stay through winter in places as cold as Pennsylvania, yet most northern birds fly south to Mexico and the southern states. Winter flocks can exceed a million birds, and breeding pairs may top 250 million in good years, which is why some call it North America's most numerous land bird. It is also one of the most thoroughly studied wild birds anywhere. Despite the name, it is unrelated to the European redwing and the Old World blackbird, which are thrushes.
Linnaeus described it as an oriole in 1766, and Vieillot moved it to Agelaius, Greek for gregarious, in 1816; the species name means crimson. Its closest relative is Cuba's red-shouldered blackbird, and together they are sister to the tricolored blackbird of California and northern Baja. Authorities recognise 20 to 24 subspecies, most alike, though two isolated bicolored populations in California and on the Mexican Plateau look quite different, lacking the male's yellow wing band.
Adult males are glossy black with red shoulder patches, flashed in flight and display, backed by a pale yellow bar; first-year males show smaller, more orange spots and are usually subordinate. Males run 22 to 24 centimetres, females only 17 or 18, and females are streaky dark brown, paler below. Birds do not gain full adult plumage until after their first breeding season, unlike most North American songbirds. Tricolored males differ by a darker red patch edged in white. The species is polygynous and eats mostly seeds and insects.
The red comes from pigments the birds make themselves, chiefly astaxanthin at 35 percent of the total and canthaxanthin at 23 percent, mixed with dietary lutein and zeaxanthin. Strip those away experimentally and the feathers turn deep brown, because they also hold melanin, mostly eumelanin, an unusual combination for carotenoid ornaments.
Source: Red-winged blackbird
