24 THE TUNDRA AND ITS FAUNA 
sea, and the glutton (Gulo luscus), a forest mammal, 
which just reaches the tundra. 
Among the mammals which find their food in the sea, 
we must place the polar bear. As its name (Ursus mari- 
timus) indicates, this animal haunts the margin of the 
sea, where it is found among the drift and floe ice, on 
the look out for its natural prey, seals and the walrus. 
It is thus not in any true sense a tundra animal, al- 
though occurring round the margin of the tundra region 
throughout its extension. Of the many kinds of seals 
also, we can only say here that though they breed on 
the shore they are not in any sense tundra animals. 
We may pass next to the birds of the tundra. In 
regard to these it is noticeable that large numbers of 
migrants occur, especially sea birds and those which 
haunt the vicinity of the shore or of fresh water. 
These come north to breed in the relative security of 
the tundra, and also probably because they find the 
long northern daylight an advantage, for it lengthens 
the period during which the search for food can be 
carried on. As winter approaches, these birds travel 
southwards, fleeing from the increasing cold and dark- 
ness. It is unnecessary to give lists of these migratory 
forms. All travellers to tundra regions, whether to the 
mainland areas or to the lands of the polar sea, speak 
of many kinds of gulls,‘of skuas, of kittiwakes, of 
geese, of various forms of ducks, including the eider, of 
auks and guillemots, of sandpipers, terns, petrels, and 
so forth, none of which can be regarded as definitely 
characteristic of the tundra, though their summer 
abundance at certain special localities is one of the 
features of the region. It is,otherwise with the true 
land birds, which, though relatively few in number, 
help to give its characteristic facies to the region. First 
