When mention is made of “waterfowl” we are likely to think “ducks and geese.” Actually, the common domestic waterfowl include four different species.
Domestic goose breeds descend from two separate wild ancestors. Embdens, Pilgrims, Romans, Toulouse, Pomeranians, and other common breeds descended from the European Graylag (Anser anser); while Chinese and African geese descended from the Asian Swan Goose (A. cygnoides). An identifying characteristic of the latter is a large, forward-inclining knob that develops where the upper bill meets the skull. (Two feral species—the Canada and the Egyptian—have also been domesticated and are kept by some hobbyists.)
All true ducks share the same ancestor—the wild mallard (Anas platyrhynchos). Though referred to as “ducks,” Muscovies have an entirely different wild ancestor, Cairina moschata—considered by some more closely related to geese than to true ducks. (They can mate with true ducks, though the offspring are likely to be sterile, like mules. In southwest France, Muscovies and Pekin ducks are crossed to produce prized Moulard ducks.)
I have raised all four of these species and recommend them if you are looking for fowl that are easy to raise, take advantage of foraging opportunities, and have lots of personality. Some flocksters such as Carol Deppe (in The Resilient Gardener) prefer ducks to chickens as working homestead partners.