The shelducks are a group of larger often semi-terrestrial waterfowl, which can be seen as intermediate between geese (Anserinae) and ducks. They are mid-sized (some 50–60 cm) Old World waterfowl. The sexes are colored slightly differently in most species, and all have a characteristic upperwing coloration in flight: the tertiary remiges form a green speculum, the secondaries and primaries are black, and the coverts (forewing) are white. Their diet consists of small shore animals (winkles, crabs etc.) as well as grasses and other plants. They were originally known as "sheldrakes", which remained the most common name until the late 19th century. The word is still sometimes used to refer to a male shelduck and can also occasionally refer to the canvasback (Aythya valisineria) of North America.
The genus name comes from the French name Tadorne for the common shelduck. It may originally derive from Celtic roots meaning "pied waterfowl", essentially the same as the English "shelduck". The namesake genus of the Tadorninae, Tadorna is very close to the Egyptian goose and its extinct relatives from the Madagascar region, Alopochen. While the classical shelducks form a group that is obviously monophyletic, the interrelationships of these, the aberrant common and especially raja shelducks, and the Egyptian goose were found to be poorly resolved by mtDNA cytochrome b sequence data; this genus may thus be paraphyletic.
- Ruddy shelduck (Tadorna ferruginea)
- South African shelduck (Tadorna cana)
- Australian shelduck (Tadorna tadornoides)
- Paradise shelduck (Tadorna variegata)
- Crested shelduck (Tadorna cristata) - possibly extinct (late 20th century?)
- Common shelduck (Tadorna tadorna)
- Raja shelduck (Tadorna radjah)
Fossil bones from Dorkovo (Bulgaria) described as Balcanas pliocaenica may actually belong to this genus. They have even been proposed to be referable to the common shelduck, but their Early Pliocene age makes this rather unlikely.