Male: jet-black mantle and pointed wings; rest of plumage glossy white. Female: dark brown where male is black; black wing underside; black spots on head; duller overall in winter. Very long, pink-red legs diagnostic; extends much beyond tail in flight. Gregarious; large numbers, often along with other waders in wetlands; long legs enable it to enter relatively deep water; clumsy walk; submerges head when feeding; characteristic flight silhouette.