Very similar to Red-winged Blackbird. Male entirely glossy black with red shoulder patch bordered by white, not yellow. Female dark brown and streaky, larger and darker than any sparrow. Lacks warm tones to plumage, unlike female Red-winged Blackbird. For both sexes, note relatively thin, sharp bill. Found in marshes and adjacent fields; breeds in colonies. Undergoing significant population decline due to habitat loss. Song is nasal and low-pitched, not as complex or as musical as Red-winged.