Small trees are eaten more completely than larger, woodier ones. Beavers cannot cut trees and make them fall in a certain direction. Beavers build dams on streams and creeks. This building behavior appears to be instinctive rather than learned. A dam backs up a barrier of water around the beaver's home lodge, much like a moat around a castle.
Dams require periodic maintenance, especially after heavy rains and during snow melt.
For shelter and rearing young, beavers construct lodges. These are dome-shaped islands of sticks and logs plastered with mud. The mud freezes in winter, making the lodge impregnable to predators that might visit. Beavers are generally congenial, although rivals fight during the February-March breeding season. Females are believed to be monogamous, while some authorities think males may breed more than one female.