THE Sheld-Ducks, Sheldrakes, Shiel-ducks or Shieldrakes, as they are variously termed, are birds of considerable size. The sexes are closely alike in colour, and they have only the ordinary autumn moult. They have rather long legs, and are able to walk fairly well. The feathers of the crown of the head are somewhat lengthened.
Of the six species of Sheld-Ducks known, four are restricted to areas within which they are resident. The other two are seasonal visitors to India, but are resident in many parts of their wide range. The Sheld-Ducks may therefore be considered a family of Ducks in which the migratory instinct is disappearing. The primaries of all the species of this group are black.
The two Indian Sheld-Ducks differ from each other in several respects. In the Common Sheld-Duck (Tadorna), the upper outline of the bill is very concave ; the bill is broader near the tip than at the base, and is furnished, in the male, with a fleshy knob which increases in size with age, but is always much larger at the nesting season than at other times; the legs ate flesh-coloured. In the Ruddy Sheld-Duck (Casarca), the upper outline of the bill is nearly straight; the bill is of equal width throughout, and is not furnished with a knob at any age; the legs are dark in colour.
The term Sheldrake, according to John Ray, who published a small book in 1674, entitled " A Collection of English words not generally used," as quoted by Mr. Stevenson, is derived from the Suffolk word sheld, which means flecked or parti-coloured. In Suffolk, a cat of the colour usually called " tortoise-shell" is spoken of as a " sheld-cat."