Shelduck

The shelducks, genus Tadorna, are a group of large birds in the Tadorninae subfamily of the Anatidae, the biological family that includes the ducks and most duck-like waterfowl such as the geese and swans.

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 different 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", this 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.

Systematics
The genus name Tadorna comes from Celtic roots and means "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.