As winter settles in on the mountains, a thin skim of ice begins to form on the edges of the quiet water on cold nights. Then one night it freezes completely over. This causes the beavers no inconvenience at all because if on one of their underwater excursions they should wish to surface for air, they have but to swim to a shallow place with firm bottom, and with one quick lift of their powerful muscles break a hole through the ice with their backs. They can break surprisingly thick ice in this way. The beavers live in comfort and plenty throughout the winter. The living room of the lodge has been furnished with comfortable beds of the cattails that have already become established along the edge of the pond. The lodge, although tightly built, still admits enough air for the beavers and food is stored in plenty on the bottom of the pond. As the bark is gnawed from the aspen branches, the bare poles are added to the bulk of the house or used in further construction of the dam. Before long, the mild southwestern winter merges into spring. In late spring the beaver family is considerably increased by the arrival of four miniature beavers. They weigh but 1 pound each at birth and are fully furred. At this time, the father is ostracized and the mother and her young live together in the lodge. When the young are about 3 weeks old, they take to the water for the first time. They quickly learn the beaver method of swimming; this is to kick with the hind feet and let the forelegs trail loosely alongside the breast, using the flat tail both as elevator and rudder. The young beavers are called kits, and indeed are as playful as true kittens can be. It is most amazing to watch them cavorting about in the water with as much ease as youngsters of other mammals do on dry land. As autumn nears, this play is exchanged for the sterner duties of existence, and the young take their places as adults of the family.