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The shelducks, most species of which are found in the genus Tadorna (except for the Radjah shelduck, which is now found in its own monotypic genus Radjah), are a group of large birds in the Tadornini tribe of the Anatidae, the biological family that includes the and most duck-like waterfowl such as the goose and .
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 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 Radjah sheducks, and the Egyptian goose were found to be poorly resolved by mtDNA cytochrome b DNA sequence data;Sraml, M.; Christidis, L.; Easteal, S.; Horn, P. & Collet, C. (1996). Molecular Relationships Within Australasian Waterfowl (Anseriformes). Australian Journal of Zoology 44(1): 47-58. (HTML abstract) this genus may thus be paraphyletic.
The Radjah sheduck, formerly placed in the genus Tadorna, is now placed in its own monotypic genus:
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.
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