The beaver, the industrious aquatic mammal known for altering his landscape much like a human, has performed one of North America's most remarkable ecological feats: recovery from near extinction.

Beavers numbered anywhere from 60–400 million prior to European colonization, but colonists in eastern North America so coveted the animal's thick, waterproof fur that the beaver was nearly trapped right out of existence. In fact, beaver pelts were so valuable that, for a time, they were even used as standard currency. By the early 1900s, the beaver population had dropped to as few as 100,000 due to overtrapping and land clearing, which largely destroyed their wetlands habitat.

Today, with their population rebounding, beavers are now recognized as a "keystone" species—one that fundamentally supports an ecosystem. However, as beavers return to long-abandoned watersheds, conflicts with humans increase, even though these aquatic animals have more in common with us than we might want to admit. We both substantially alter the environment for our own benefit. Though our dramatic alterations to the landscape ensure that the beaver population will never return to what it once was, these determined animals are reclaiming parts of their former range and are now more common in urban and suburban wetlands.

Beaver Basics

The largest rodent in North America, the beaver (Castor canadensis) can tip the scales at more than 60 pounds, although an average adult weighs 35–40 pounds. An adult beaver can be nearly three-feet tall when standing on his hind legs.

Found in wetlands throughout most of the United States and Canada, beavers are well adapted to an aquatic habitat. They're excellent swimmers, able to hold their breath for as long as 15 minutes. Beavers also have large, webbed hind feet; valves in their ears and nostrils that form a watertight seal; and dense, waterproof fur. A flap of skin behind their front teeth even prevents them from swallowing liquid when carrying wood underwater.

Beavers are also known for their large front teeth, whose exterior surface is covered in bright orange enamel. Although their long incisors may look menacing, beavers are completely herbivorous mammals, and generally peaceful creatures. Their ever-growing front teeth are worn down to a chisel-like edge by regular gnawing on trees, a plant that provides both food and shelter. Beavers feed primarily on the inner bark of woody plants, but also eat leaves, shoots, duckweed, water lilies, and pondweed. Of course, beavers are also famous for their unique, flat tails, which they use as balancing tools and communication devices—slapped on the water surface, the tails effectively signal danger.

Beavers typically live in lodges constructed from branches, mud, and other debris, or in dens dug into the banks of streams or lakes. Lodges may be created along the edges of canals or ponds, or formed as mounded islands of interwoven branches that stand further out in deeper water. The structures are packed solid with mud to make them weatherproof—except for the peak, which is left open for ventilation—and have at least two or more water-accessible openings.

In the fall, beavers stockpile winter food supplies by sinking large amounts of branches into the mud close by their lodges or dens. With a sizable underwater cache, beavers can remain comfortably well-fed even during the harshest winter freeze. They simply swim beneath the water's icy surface to retrieve choice branches, then devour them inside the lodge.

For beavers, dam-building is an instinctive survival skill. The main purpose is to surround themselves with a stable body of water—understandably important to animals who are far more adept in water than on land. The resulting pond provides beavers with a safe refuge from predators; flooding an even larger area also ensures watery access to prime food sources in the vicinity.

Beavers produce one litter per year, usually between March and June. A typical litter contains three or four kits. After kits are weaned, parents and older offspring who remain with the family share parental duties. A beaver colony usually has six to eight animals: an adult pair and the kits from the previous two litters. Older kits usually leave the colony by their second birthdays. Most generally travel less than six miles to find new homes, but some beavers have been documented to have traveled as far as 150 miles.

As part of our "Living in Harmony with Your Wild Neighbors" series, The HSUS has published a full-color pamphlet on beavers. To request your free copy, email them at wildlife@hsus.org.