"The whistling ducks or tree ducks are a subfamily, Dendrocygninae, of the duck, goose and swan family of birds, Anatidae. They are not true ducks. In other taxonomic schemes, they are either considered a separate family, Dendrocygnidae, or the tribeDendrocygnini in the goose subfamily Anserinae. The subfamily has one genus, Dendrocygna, which contains eight living species, and one undescribed extinct species from Aitutaki of the Cook Islands."
You could actually say its more of a goose than a duck.