Beavers built dams long before men did

big beaver
  Men were not the first builders of dams. Beavers built dams long before men did. Beavers are clever engineers.
  Beavers build their homes in ponds. The dams they build hold back the water in streams and make it form ponds. There may be 25 or 30 beaver homes in one pond formed by a beaver dam.
  These animal engineers work together to build their dams. They pile up logs and twigs, weight them down with stones, and fasten them in place with mud. They pat the mud into the cracks with their noses and feet. They work on a dam until it is so solid and high that very little water goes through it or over it.
  Beavers build their homes, too, of branches, twigs, and mud. One of these homes looks like a big pile of branches out in a pond. It is really a one-room house with doors in the floor. Beavers must swim down into the water to get in or out.
  To get logs for their homes and dams, beavers cut down trees. They belong to the group of gnawing mammals, or rodents.
  They have four long, sharp teeth that are like chisels. To cut down a tree a beaver gnaws around and around it. The beaver works until it has cut a deep ring around the tree. When the tree shivers, the beaver slaps the ground with its tail. The slap warns other beavers that the tree is about to f all. Down it comes! Now many beavers work together cutting it into pieces.
  Beavers cut down trees not only to build dams and homes, but also to get food. They eat the bark of the trees. They may also eat the wood itself. The beavers store logs and branches in the water near their homes. They pile stones on the branches to hold them down. Poplar trees make the best food for beavers.
  Beaver dams create ponds in which the beavers build their houses.
  Some of the beavers in a pond may live by themselves in homes in the bank instead of in "log" houses. The homes in the bank are long tunnels.
  During the winter beavers stay in their homes most of the time. They leave their homes only to get food from their store-houses. But when spring comes they are "as busy as beavers" again.
  Beavers have beautiful fur. To get their fur we have killed far too many beavers for our own good. For beavers, while they are building dams to help themselves, are helping us, too. Their dams hold back water, prevent floods, and keep good farmland from being washed away. The soil that they save for us is worth much more than their fur.