Beavers need trees and shrubs as building material for dams, which impound flowing water to create a pond for them to live in, and lodges, which provide shelter and protection. Without such material, beavers dig burrows into a bank to live. Construction begins in late summer or early fall, and they repair them whenever needed. Beavers can fell trees wide or less in under 50 minutes; trees as large as can require over four hours. When chewing down a tree, beavers bite the trunk at a 45-degree angle and chew with the side of the mouth; alternating between the left and right sides. Tree branches are cut and carried through land and water using the powerful jaw and neck muscles. Other building materials, like mud and rocks, are carried under the chin with the forelimbs.