On page 91 I have referred to some birds which have come to us from the north. One of these, the Snow Bunting (_Plectrophenax nivalis_), is a typically Arctic species. In summer it is widely distributed, and is found in Spitsbergen, Novaya Zemlya, Siberia, and the Arctic Regions generally. In winter it migrates down into North America, into Japan, Northern China, Turkestan, Southern Russia, and occasionally even across Europe into North Africa. Very characteristic Arctic birds are the Eider Ducks belonging to the genus _Somateria_. Three species have visited the British Islands. The common Eider Duck (_S. mollissima_), which is of such high commercial value, is abundant in Norway and northward, throughout the Polar Regions. The appearance of the King Eider (_S. spectabilis_) on our coasts is an extremely rare occurrence, and even in Norway it is only known as a visitor, but on Novaya Zemlya and along the Arctic shores of Siberia, in Greenland and Arctic North America, it is known to breed. The third species, Steller's Eider (_S. Stelleri_), seems to be still rarer, and only in the Aleutian islands and in the north of Alaska can it be said to be at all abundant. It is probable that the famous Great Auk (_Alca impennis_, Fig. 9) also was a typical Arctic species. Its range extended to both sides of the Atlantic. In Newfoundland and on the coast of Iceland it is known to have been met with in considerable numbers within historic times; and no doubt, like all Arctic species, it extended farther southwards at a more remote period. [Illustration: Fig. 9.--The Great Auk (_Alca impennis_).] The members of the genus _Lagopus_, including the various species of Grouse, are likewise of northern origin. The British Red Grouse (_L. scoticus_), which may be looked upon as a form of the Scandinavian Willow Grouse (_L. albus_) (compare p. 91), constitutes in some respects a curious case of parallelism with the Arctic Hare, since the latter, in its more southern station, generally retains the summer fur throughout the year. The allied Ptarmigan (_L. mutus_) inhabits Scandinavia, the Ural Mountains, and some of the Asiatic mountain ranges. It is also found in the European Alps and in the Pyrenees. The North European range of the Ptarmigan suggests that we are dealing with an ancient species which came south from the Arctic Regions at about the same time as the Arctic Hare; but it is more probable, as I have shown in a subsequent chapter (p. 334), that this species has entered Europe more recently with the Siberian migrants from Central Asia, where indeed the genus had its original home. The Black Cock (_Tetrao tetrix_) and the Capercaillie (_Tetrao urogallus_) have also come to us from the east, and have even penetrated into Ireland. They are therefore some of the few instances of members of the Siberian invasion having become temporarily established there.