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Beavers are known for building dams, which the animals construct from trees and branches they cut with their strong incisors, according to the National Park Service (opens in a new tab). The rodents also use grass, rocks and mud to reinforce these structures.
But why do American beavers (Castor canadensis) build dams? Do they live in them?
Simply put, beavers build dams to stay safe, which is especially challenging given their awkward body shape and clumsy nature. “Beavers weigh 40 to 80 pounds [18-to-36 kilogram] smelly meat bags with very short legs,” Chris Jordan (opens in a new tab)a fisheries biologist at the National Oceanic and Atmospheric Administration (NOAA) Northwest Fisheries Science Center in Newport, Oregon, told LiveScience in an email.
That makes these large rodents easy prey. “When beavers are on the land, they are very awkward and vulnerable, like big lumps of chicken waddling around that any predator would love to have as a meal.” Emily Fairfax (opens in a new tab), an ecohydrologist at California State University Channel Islands in Camarillo, Calif., told LiveScience in an email. “But when they’re in the water, they’re almost invincible. They’re excellent swimmers and can hold their breath for 10 to 15 minutes. By building a dam, they create a pond, and that pond is their safety zone.”
These bodies of water are deep enough for beavers to hide from predators, such as mountain lions, bearswolf and coyotes, Jordan said. Damming can also flood areas to bring beavers closer to their main food source, he noted. This includes the bark, leaves and twigs of trees, as well as aquatic plants, such as water lilies and cattails, according to a fact sheet from King County, Washington (opens in a new tab).
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Furthermore, “beavers dig extensive channel networks behind their dams to disperse the water,” Jordan said. This can safely bring them closer to trees, but it also “helps transport larger pieces of food and building materials back to the lodge, dam and food buffer.”
Although dams protect beavers, they do not live in these structures. Instead, they often live in oven-shaped huts made of sticks, grass, moss and mud built in or on the banks of the ponds they created, according to the University of Michigan’s Animal Diversity Web online database (opens in a new tab). In these cabins, they live in family groups, known as colonies, consisting of an average of five beavers, the King County site says.
The Eurasian beaver (Castor fiber), which lives in Europe and Asia, is slightly larger than the American beaver. It also builds dams, huts and canals, a 2020 study in European Journal of Wildlife Research (opens in a new tab) noted.
Beaver dams help ecosystems
Beaver ponds benefit not only their creators, but also many other species. “Beaver dams help slow down the water and keep it on the landscape longer,” Fairfax said. “This transforms simple streams into thriving wetland ecosystems. The amount of food and water available in their wetlands makes them ideal habitat for many different species. That’s part of the reason beavers are what’s known as a keystone species.”
Ultimately, returning beavers to their original habitats can help reduce the effects of Climate changes and benefit from their ecosystems in many other ways, Fairfax and Jordan noted in an April 2022 perspective article in the journal WIRE’s Water (opens in a new tab).
“When their dams slow down the water, some of it is stored in the soil, where plant roots can access it even during drought“, Fairfax said. “It helps keep the vegetation lush, so when wildfires start, the beaver complexes are uniquely resistant to burning. These fireproof patches help preserve intact ecosystems; provide refuge for animals that cannot escape, fly or swim away from the fire; stabilize riverbanks after fire; and help trap and settle ash and sediment suspended in streams after the fire.”
In addition, vegetation from beaver dams can pull greenhouse gas carbon dioxide from the air and reduce flood damage, the researchers noted. When all of this beaver-linked data was examined together, “it was remarkable how well suited beavers are to not only survive changing climates, but also to do some of the climate change adaptation work that we as humans have been trying to do ourselves,” Fairfax said.
“My big takeaway from that is that we are not alone in our efforts to restore ecosystems and build resilience to climate change,” she said. “Beavers, and probably other ecosystem engineers and keystone species, do similar things through their own innate abilities. More progress will be made if we work with them rather than against them.”
