Why do beavers build dams and what are they made of?

Beavers make their complex domestic arrangements to improve security from predators and to move and store a reliable food supply.

Dam building is only one of their construction activities, along with canal building and lodge building.

The dammed-up ponds make an important contribution to the beavers’ well-being by creating storage at the right depth to stash a winter’s supply of bark, twigs, roots, and leaves at temperatures above freezing, but cool enough to keep their nutrient value intact.

The ponds also improve security and must be deep enough for a family of beavers to swim under winter ice from their lodge to the hidden food.

The dams are constructed by moving mud, stones, sticks, and branches across a shallow stream. Beavers use their forepaws to move mud and small stones from the stream bottom to the dam site.

Large sticks and branches are towed to the site with the beavers’ large incisors and are used to support the dam and keep the other components in place.

The females are the most active in dam building, though all adults and yearlings may take part. Most construction takes place at night.