How do beavers survive Minnesota winter?

As you bundle up for the cold weather, consider the American beaver, whose pelts once provided one of the best ways to stay dry and well insulated in the winter.

That insulated fur helps beavers, North America’s largest rodent, survive freezing temperatures in and out of the water as they gnaw down the last trees of the season.

“A lot of their time [in late fall] is sticking branches and other vegetation into the mud of the pond so they have access to food all winter long,” said Jason Abraham, fur-bearer animal specialist for the Minnesota Department of Natural Resources. The mud helps preserve their food supply, which often includes alder, birch and willow.

Chewing wood keeps beavers’ ever-growing orange teeth at a reasonable length. Their distinctive flat tail provides a rudder when swimming, offers some stability when felling trees, and serves as a warning when slapped loudly. They also have a special toe on their hind leg to help them comb oils from a castor gland across their fur for waterproofing. Their lungs are strong enough that they can stay underwater for about 20 minutes, which can be essential for building lodges.

The nocturnal creatures use trees to dam waterways and create a pond that surrounds their lodges and keeps them safe from predators. Sticks, rock and mud are piled tightly together, but loose enough for air holes on top. The lodges must be spacious enough for a mated pair, their growing kits, and sometimes a female kit or two from the spring before. Most lodges include two underwater entrances big enough for the adults, which can grow up to 60 pounds.

A remote beaver lodge in Canada grew so big it can be seen from satellites, but most beaver lodges average about 6 feet high to about 12 feet wide.

While beaver dams can cause problems for landowners, they’re considered a keystone species for creating placid ponds and ecosystems where diverse plants and wildlife, including small fish and waterfowl, can thrive.

“They create all kinds of habitats,” Abraham said. “There’s definitely a give and take with their dam building.”

Lisa Meyers McClintick of St. Cloud has freelanced for the Minnesota Star Tribune since 2001 and volunteers as a Minnesota Master Naturalist.