THE LIFE OF MAMMALS 
that when the mass freezes the enormous strength of a bear or 
wolverine is hardly able to break it down; but in summer both 
these marauders, and especially the latter, frequently tear it to 
pieces. The domed chamber within an old house will be six 
or seven feet in diameter, and in winter is snugly bedded with 
grass. Such a house stands a great many years —is a per- 
manent habitation, in fact; but never contains at once more 
than one family, which consists of the parents and two suc- 
cessive broods of young; the third year the oldest youngsters 
leave, or are driven out to set up for themselves. In summer, 
however, when the babies are arriving, the old “buck” beavers 
all leave home and wander widely, keeping (or kept) away from 
their wives and little ones. 
There is, then, no real community life, even in a large beaver 
colony, except in the ownership and care of the waterworks, and 
there each works as he pleases, though all share the benefit of 
his labors. Each separate family builds and repairs and occu- 
pies its own lodge, and provides its own store of food. 
This food, as I have said, is mainly birch, poplar, and maple 
bark, and it can be obtained only by gnawing down trees. This 
the beavers do as often as necessary, but mainly 
late in autumn, in preparation for the impending 
winter. At that season they attack large trees, — sometimes 
eighteen inches in diameter, — and gnaw them off by standing 
on their hind legs and biting all round them until they fall. 
Having felled a tree, the family busies itself in saving a store 
of bark for winter use. For this purpose the smaller brushy 
parts of the limbs are first cut off and dragged or floated nearly 
to the door of the house, where they are sunk to the bottom of 
the pond, and somehow fastened there. The larger limbs are 
then cut into manageable lengths and put into the same place; 
and there they stay until one by one, during the winter, they are 
dragged into the lodge and stripped for food. Then the de- 
nuded logs are thrown out and form the materials for repair 
466 
Food. 
