Understandably also known as Knob-billed Ducks, the unusual Comb Ducks are named for the prominent, leaf-shaped caruncle or fatty comb atop the basal two-thirds of the drake's black bill, a structure clearly evident even in flight. While flaccid and reduced in size for much of the year. These fleshy combs enlarge considerably prior to the breeding season, when caruncle size presumably indicates the general vigor of males. Drakes are twice the size of females, and their dark dorsal surfaces are glossed with dazzling metallic-violet, purple, bronze and green. There appear to be two distinct species probably originating from Africa these ducks can migrate for 2,500 miles Taken at Slimbridge Wildlife wetlands reserve in the UK