The mammals of Shetland are comparatively few. There are no deer, foxes or badgers. Rats and mice are numerous, hedgehogs are fairly common. Moles and bats are unknown. So, too, are snakes, lizards, frogs and toads. The weasel is found in many districts, and its near relative, the ferret, is used for hunting rabbits, which are plentiful everywhere. Hares were imported some time ago, but have a hard struggle for existence with so many enemies around. Along the shore may occasionally be seen the sea-otter, when he comes up on a rock to enjoy a feast of sea-trout, or to venture inland in search of fresh water. He must needs be wary, as he is greatly sought after for the sake of his valuable skin. Another amphibian is the seal, whose habitat is the base of inaccessible cliffs and out-lying rocks and isles. [Illustration: Kittiwakes. Noss Isle] The birds of Shetland may be divided into residents, summer visitors, and winter visitors. In the great annual migrations which take place in spring and again in autumn, the islands form a resting-place for the feathered voyagers, some of whom stay to nest. Sea fowl naturally predominate. The gull family is the most numerous and includes the great black-backed gull, the lesser black-back, the herring gull, the common gull, the black-headed gull and the pretty kittiwake. Shags (scarfs) and cormorants are abundant all the year round; and in their season come the guillemots, razorbills, puffins, manx shearwaters and little auks. The guillemots congregate in thousands on the rocky ledges of cliffs, where each female lays a solitary egg on the bare rock. The egg is so formed that, even if disturbed, it will not roll off the shelf on which it lies. The plumage of the black guillemot or “tystie” during the winter season is of a mottled-grey colour, and the bird is difficult to recognise in its changed appearance. Eider ducks are abundant, and the great northern diver (emmer goose) may often be seen. [Illustration: Shag on Nest. Noss Isle] Colonies of fulmar petrels are spreading all round the coast, while the stormy petrel comes to nest in the outer islands. The piratical skua is common; and the great skua, which is strictly protected, is on the increase in certain localities. Among the shore birds may be mentioned the noisy terns and oyster-catchers. In the winter come the turnstones, sandpipers, dunlins and redshanks. Among the divers may be noted the golden-eye, merganser, and long-tailed duck, while the stock-duck, teal and widgeon are fairly plentiful.