As offering another step in the transition between the Geese and Ducks, and making any sharp line between them impossible, we come to the Shelldrakes (Tadorna), of which two species are known. They are large, strikingly handsome birds, natives of the Old World, with rather long legs in which the tarsus is covered in front with transverse scutes, thus conforming in this “Duck-like” character to the true Ducks. They agree with the Geese, however, in the plumage of the sexes being similar, and the male retaining the same dress through-out the year. They agree with the Tree-Ducks in having a narrow membrane connecting the toes, and in the single annual moult. The best-known and most widely distributed is the Common Shelldrake (T. Tadorna), which spends the summer from Europe to southern Siberia and Japan, and the winter in Africa, India, and China. It is about twenty-six inches long and has the upper back chestnut, the lower back, rump, upper tail-coverts, and tail white, the latter black-tipped, the scapulars, a part of the secondaries and the primaries black, the wing-coverts white, the head and upper neck glossy green, followed by a broad white collar, while the lower parts are dark brown and black. The bill is provided with a prominent knob, which, together with the bill itself, is bright red. It inhabits the sandy seacoast, feeding on mollusks and marine insects. Curiously enough they nest in burrows, sometimes excavating them for themselves, but oftener making use of the abandoned holes of rabbits and foxes. The burrow is from six to twelve feet long and ends in a chamber, which is lined with dry grasses, moss, and quantities of down plucked by the female from her own body. The eggs are from seven to twelve, creamy white in color. The other species (T. Radjah) is smaller, is without the knob on the bill, and has the whole head and neck white. It occurs in New Guinea and Australia, and, according to Gould, makes its nest in hollow trees.
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