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America's largest rodent may be clumsy on land, but in water, it's a marvel of design.
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America's largest rodent may be clumsy on land, but in water, it's a marvel of design.

Thank goodness for fickle fashion. If beaver hats hadn't gone out of style in Europe in the 1830s, fur traders might have trapped North America's largest rodent to extinction–bad news for the scores of animals that depend on the nutrient-rich wetlands these natural engineers create. Beaver dams also help filter water, reducing pollution and keeping sediment from clogging downstream lakes. With its chisel-like front teeth and waddling gait, the 45-pound mammal might look clumsy on land, but its sleek shape and muscular tail make it a graceful swimmer that can double the average human's best freestyle pace. Look for the resourceful beaver from coast to coast, up to treeline, in waterways surrounded by deciduous trees.

Adaptations

Humans would need flippers, goggles, earplugs, nose plugs, and a wetsuit to approach a beaver's underwater aptitude.

Eyes, ears, nose A beaver's nostrils and ears shut to form watertight seals, while clear eyelid membranes allow the animal to see while traveling underwater.

Mouth Lips close behind the front teeth, enabling beavers to carry sticks while swimming.

Hind feet Powerful webbed feet propel beavers through the water.

Coat Thick, water-resistant fur insulates in icy ponds.

Tail The scaly black tail serves as a rudder, moving slowly back and forth to steer. On shore, beavers slap their tails against the water's surface at signs of danger, issuing a gunshotlike warning.

Beaver Watching

Fresh mud on dams and lodges, gnawed trees, and well-worn trails to favorite groves indicate an active colony. Scope the site in the late afternoon and early evening, when beavers–which usually become active at dusk–start to come out. As the autumn gets cooler, they often emerge during the last few hours of daylight to stockpile food and winterize the lodge. "It's almost as if they feel the pressure of winter is coming on them," says Douglas Smith, a Yellowstone biologist who has studied beavers for more than a decade. Beaver hotspots include Voyageurs National Park (MN), Rocky Mountain National Park (CO), and the Adirondacks (NY).

Home Sweet Lodge

Inside a beaver's custom-built shelter

Beavers eat water plants and a tree's bark, twigs, and a soft inner layer of cells (called the cambium), gnawing on sticks the way people eat corn on the cob. As winter nears, beavers begin building a food cache, storing their favorite aspen and willow branches in underwater piles next to the lodge. When ice covers the pond, a fresh meal is only a few feet away.

On land, slow-moving beavers are easy prey. But in the pond, underwater tunnel entrances keep predators like wolves, bears, and coyotes at bay.

Some beavers burrow lodges into the banks of streams and lakes; others build their own islands in the center of a pond. These lodges, made from sticks and vegetation woven together with mud, can be eight feet across and three feet high. Beavers pad the inner chambers with wood chips and even poke holes through the roof for ventilation.

Families consisting of a monagamous pair, their yearling offspring, and newborn kits all share one lodge. Babies are born April through June and can swim within a few days, venturing out of the lodge with their parents in midsummer.