The Blue Duck (Hymenolaimus malacorhynchos) is a member of the uck, goose and swan family Anatidae. It is the only member of the genus Hymenolaimus, placed in the shelduck subfamily Tadorninae after previously being considered part of the paraphyletic "perching duck" assemblage. The Māori name is whio, which is an onomatopoetic rendition of the males' call.