Beavers are unique among mammals in that they alter their habitat to meet their needs by damming streams to form ponds. This behavior actually benefits other species (including people), as well. By building dams and flooding woodland swamps, beavers play an important part in the restoration of lost wetlands (over 50 percent of our wetlands have disappeared since European settlement in North America), providing habitat and food for a wide variety of plants and animals.
Beavers build their dams in order to create deep ponds that won’t freeze at the bottom in winter. Within these ponds, they build lodges to provide protection for the young in summer and for the entire colony in winter. Lodges are large structures, from 15 to 40 feet across and three to six feet above the water. They line the living space (located above the waterline) with dry plant material. Entrances are located underwater.
Because of the flooding beavers create, trees often die off, providing nesting sites for Great Blue Herons, Wood Ducks, Tree Swallows, and other birds. These new ponds become homes to amphibians, turtles, fish, otters, muskrats, and other animals.
Beaver-created wetlands also enhance human habitat by storing and slowly releasing floodwater, which controls downstream flooding. They improve water quality by removing or transforming excess nutrients, trapping silt, binding and removing toxic chemicals, and removing sediment. And finally, flooded areas can also recharge and maintain groundwater levels, and provide flow to streams even during droughts.