coscoroba swan

— The coscoroba swan is the smallest swan, and it is recognized by its bright-red, flattened, ducklike bill and its red legs, which are the longest in relation to body size of any swan species. Coscoroba swans share some characteristics of whistling ducks [...]. Consequently, many authorities regard the coscoroba swan as a sister species to true swans; the coscoroba swan bears the closest affinities to the whistling ducks.