by Janice Welsh
Have you ever heard the saying "busy as a beaver?"
The beaver, Minnesota's largest rodent, works year-round. We know beavers are busy because we can see the evidence: dams, lodges, and fallen trees. From late summer through the fall, beavers are getting ready for winter. They build their homes, fix their dams, and gather and store branches for food.
Unlike other mammals, beavers grow throughout their lives. A full-grown beaver can weigh about 60 pounds. That's as heavy as a large dog. In the wild, a beaver might live five years and weigh as much as 90 pounds.
All rodents, including beavers, have front teeth called incisors that keep growing all their lives. Constant gnawing and gnashing wears down their teeth and keeps them even.
During the summer, beavers chomp on water plants. In the late summer and fall, they cut down trees by chewing all around the trunk. They chew the trees into smaller pieces to make the wood easier to carry. Then they pile the branches in the water or stick them in the mud at the bottom of the pond for the family's winter food supply.
Beavers eat the bark on the branches the way you eat corn on the cob. They do this to get at the nutritious layer between the bark and the wood. They add the bare branches to their dam or lodge. Their favorite trees are willow, aspen, alder, birch, and maple.
A beaver is well-suited to live in its watery habitat. Thick fur and a layer of fat underneath help keep it warm during the winter. A beaver waterproofs its coat year-round with oil from a gland near the base of its tail. Using a split claw on each hind foot, the beaver combs the oil through its fur.
When the beaver is swimming, valves in its nose and ears close to keep out water. Clear membranes cover its eyes to protect them from wood chips and other things in the water. A beaver can spend 15 minutes underwater before coming up for a breath.
When a beaver gnaws bark or carries branches underwater, it lips are sealed. Folds of skin on both sides of its mouth close behind its front teeth. This keeps the beaver from swallowing pond water.
Shaped like a canoe paddle, the beaver's wide, flat tail works as a rudder for steering underwater. The tail also works as a kickstand, propping up the beaver while it chews down trees.
Webbed toes on its hind feet help the beaver swim. Like swim fins, the feet push back against the water. On the forward stroke, the webbed toes fold together.
Using sticks, mud, and rocks, beavers build a dam on a stream to form a pond. Inside their house, beavers dig out a living space above the water line. Wood chips on the floor of their lodge absorb moisture, and a vent lets in fresh air. Even in the coldest weather, the temperature inside a beaver lodge stays around 32 degrees.
Four to 10 beavers spend the winter together in a lodge. This helps them stay warm. A beaver colony includes an adult male and female, young kits, and yearlings born the previous spring.
Beavers usually give birth to four kits in May. The furry kits are born with their eyes open. They weigh about a pound. The kits can swim the day they are born. Young beavers usually leave the colony during their second year.
People paid a lot of money for beaver fur 200 years ago. Indians sold beaver pelts to European fur traders, who sent the pelts to Europe to be made into fashionable coats, robes, and beaver-felt top hats. Beaver pelts were used just like money in the wilderness.
Trappers all across North America searched for beavers. Sometimes they trapped too many, and beavers disappeared from many areas. Today some places have more than ever.
When too many beavers live in one place, beaver dams and ponds can flood farm fields and roads. People sometimes get angry when beavers cut down trees. To prevent beaver damage to trees, people can put 3-foot-tall wire-mesh fences around tree trunks. People still trap beavers for their fur and to reduce their numbers where they cause problems.
The work done by beavers can help people and other animals. Beavers create meadows and ponds used by ducks, otters, moose, and other creatures. The ponds help prevent flooding by holding spring rains.
Call local nature centers and state parks to ask about opportunities to see beavers in the wild. To see beavers at work, visit a beaver pond in the evening. Wear dark clothing, then sit quietly.
At the Minnesota Zoo in Apple Valley, you can see beavers at work during the day. You go into a room with a window that lets you watch the beavers underwater and above water. A TV camera lets you see the beaver lodge.
Janice Welsh, who wrote this story, runs the DNR's Project WILD, a program for schools.
A complete copy of the article can be found in the July-August 1995 issue of Minnesota Conservation Volunteer, available at Minnesota public libraries.