Most everyone knows that beavers cut down trees to build dams, lodges and ponds. Beavers need to cut down trees for another reason. Their teeth grow constantly, and beavers in captivity who were not allowed to gnaw on trees have actually had their teeth grow into the opposite jaw, preventing them from feeding at all. The condition is, of course, fatal. The orange-colored outer layer of beaver teeth is extremely hard and the layer behind is softer. That means that beaver teeth will stay very sharp because they wear at different rates.
Their food preferences are -- in order -- aspen, willow and birch inner bark. Once they run out of aspen and willow, however, they are usually looking for a new place to live. Adult beavers need about 200 trees each, per year, for food. There is one treat that they prefer even over aspen, if they can find it. Pond lilies have root-like tubers which look like a long, thin pineapple. Beavers dig them up in the summer and gorge themselves. In the Rocky Mountain West, the tubers are much less common than elsewhere in North America.
Mythology has exaggerated the beavers’ lumberjack skills. Some people have marveled over their ability to drop trees into the water, until they realize that trees near the water always lean out over it, looking for sunlight. In reality, quite a few beavers have been crushed under trees they cut down. Beaver dam-building gets triggered by water making noise, tumbling over rocks. Fortunately for the beavers, that is usually the narrow place in a stream, and there is usually a wider and flatter valley upstream. It often makes for the perfect home. Beaver lodges are almost always built next to the deepest place in a pond, which is, of course, the old stream channel. This location ensures that they will be able to construct their winter food pile (branches stuck into the mud) in the deepest place possible. Reason? It is below the winter ice.
Their lodges have two chambers, a lower “dining room” and a higher “bedroom”. The walls are at least two feet thick – insulation which keeps the lodge above 40 degrees F. even when it is forty below. The colder the day, the more active the beavers – living “furnaces” heating up the lodge. During the day, beavers are packed like sardines in the upper chamber. It is logical then, that when they emerge to feed in the evening, they want to be alone.
If they are usually alone outside the lodge, how do we know anything about their family life? The answer is: look for the subtleties, the fine print. Beavers communicate by smell and sound. They have castor glands in their lower belly which produce castoreum, a liquid that smells like licorice. Beavers build mud-pies called scent mounds in their main activity areas, such as near the lodge or feeding spots. If other beavers from outside the family swim by often (such as on a larger river), they will build many more scent mounds. So, technically, they don’t mark the edges of their “territory”, but only the areas where they are busiest.
Beaver young are called “kits” and are born in June. They stay with the adults until May of their second year, when they are forcibly evicted from the pond by both adults. In June, “mom” also evicts the “dad” and the yearlings from the main lodge for a month or so. She bears and raises the small kits alone. The adult male and yearlings take up residence in the “summer cabin”, a smaller lodge at the other end of the pond.
The adult female, besides (1) evicting the other beavers for a while, is (2) larger than the male, (3) builds more of the scent mounds and (4) does more dam and lodge maintenance. She also (5) emerges from the lodge first every evening, checks for danger, and goes back inside. Then, and only then, do the other beavers emerge for the night. Lastly, (6) everyone pays attention when she slaps her tail on the water surface (a danger signal). If the yearlings or kits tail-slap, no one pays much attention. If the adult male slaps, the others often swim over to investigate. When “mom” slaps her tail, everyone disappears into the lodge – now! (Mother knows best?)