(Zool.) Any one of several species of large Old World ducks of the genus Tadorna and allied genera, especially the European and Asiatic species. (Tadorna cornuta syn. Tadorna tadorna), which somewhat resembles a goose in form and habit, but breeds in burrows. Note: It has the head and neck greenish black, the breast, sides, and forward part of the back brown, the shoulders and middle of belly black, the speculum green, and the bill and frontal bright red. Called also shelduck, shellduck, sheldfowl, skeelduck, bergander, burrow duck, and links goose. Note: The Australian sheldrake (Tadorna radja) has the head, neck, breast, flanks, and wing coverts white, the upper part of the back and a band on the breast deep chestnut, and the back and tail black. The chestnut sheldrake of Australia (Casarca tadornoides) is varied with black and chestnut, and has a dark green head and neck. The ruddy sheldrake, or Braminy duck (Casarca rutila), and the white-winged sheldrake (Casarca leucoptera), are related Asiatic species.