Sunday, 1 May 2011

Report Text_American Beavers

American Beaver

The Master Builders of the Animal Kingdom

American beavers live throughout North America. They have brown fur and large, flat tails. They are among the most skilled builders in the animal kingdom. American beavers build structures called dams that stop flowing water. These dams help create wetlands. This provides habitat for mammals, fish, frogs, turtles, birds, and ducks. In fact, Native American people called the beaver the “sacred center” of the land, because beavers create rich habitat for so many species. Today, scientists view American beavers as the keystone species in wetland environments.
Beavers are master builders
Beavers are the master builders of the animal kingdom.  They change their environment to fit their needs.  Their dams stop flowing water and create ponds and wetlands.
©Tom & Pat Leeson

Sizing Up the American Beaver

Beavers use sharp teeth
Beavers use their sharp front teeth to cut down trees.  They can cut down a large tree in just one night.  After they cut down a tree, they eat the tender green bark and leaves. They use the stripped branches for their dam and lodge.
©Tom & Pat Leeson
Beavers grow to be about 120 cm long, including the tail, and can weigh up to 43 kg. Beavers keep growing throughout their lives. Thousands of years ago, some beavers of North America were about 2.3 m long. These beavers were the size of modern bears!  Beavers have been around since the time of mammoths, mastodons, and wooly rhinoceros.  Scientists have found fossils of these giant beavers in ancient wetlandhabitats.

Crafty Beavers

The beavers’ ability to change and reshape their environment to fit their needs is rare in nature. Humans and elephants are the only other animals that have such a large impact on their environment. Beavers devote a lot of time to building and maintaining their dams. A beaver’s desire to build a dam is very instinctive. Beavers in captivity will build useless dams just so they can build.  In the wild, scientists have observed beavers making “repairs” and “additions” to human-made dams. Beavers hate the sound of running water. It makes them think there could be a leak in their dam.  If they hear running water, they will often work day and night to find the leak and repair it.
Beavers collect branches
Beavers collect branches with green bark and place them in an underwater storage area near their lodge. They feed on the stored food during the winter when green plants are scarce.
©Tom & Pat Leeson

Eating As They Build

Beavers live and work near their favorite foods - aspens, cottonwoods, willows, water lily tubers, and clover. But beavers will also travel to find food.  If they find a good source some distance away, they may dig small canals from the food source to their pond. This makes it easier to transport the food. Beavers are nocturnal and do most of their dam work and food finding at night.
Beavers are herbivores. They prefer to eat tender tree shoots, leaves, and green bark. If they cannot reach the parts of a tree they want to eat, they will use their sharp front teeth to cut the tree down.  Beavers cut trees down by gnawing around the trunk in a circular pattern.  While cutting the tree, they stand on their back feet and balance themselves with their huge, flat tails.
Beavers must eat a lot of food to get the nutrition they need. A beaver may eat up to 20% of its own weight in just one day. For example, a 22 kg beaver might eat about 4.5 kg of food a day! That’s a lot of leaves and branches!
Beaver dam
Beavers use cut trees to build dams that stop or control water. They also build a lodge to live in and raise their babies in.  The lodge is dome shaped and made of sticks. It has a warm den inside. A hole in the den’s floor goes straight into the water. The lodge is most often built on a bank or small island.   
©GLOBIO.org

Built to Build

American beavers have special adaptations for living in and near water. Adaptations are also what make them so good at building dams and cozy lodges out of sticks and mud. 
©Tom & Pat Leeson

Born to Be Busy

Beaver babies are called kits. They are born in litters of about three to four.  Kits weigh between 250-600 g at birth. They are born with a full coat of fur and their eyes open. Within 24 hours, they can swim. They’re ready to get on with life!  After several days, kits are able to dive and explore some of their surroundings with their parents. But, kits still spend most of their first month inside their safe, warm lodge. During this time, they learn many important skills through imitation and experience.  Yearling beavers also help care for new kits born in the lodge.
Baby beavers
Baby beavers, called kits, are usually born in litters of three to four.  They are born with all their fur and with their eyes open.  They can swim within one day of birth but generally stay inside the lodge for the first month.
©Tom & Pat Leeson

All in the Family

Adult beavers leave their parents’ lodge when they are about three years old. They set up their own territory and find a mate. Beavers are one of the few mammals who mate for life. Both parents help take care of the babies. A family of six or more beavers all living together in a lodge is called a colony. Members of a colony communicate with each other using low groans, whistles, and whines.  Beavers usually interact and share territory only with their family group.  Most beavers live 10 to 20 years.

Beavers in Trouble

Beaver fur hats
In the 1700s and 1800s, many styles of beaver-fur hat were popular. Hunting beavers for their fur almost caused the American beaver to become extinct.
©Horace T. Martin/HBCA
Beavers are not endangered but they were once hunted to the brink of extinction. Beaver pelts (fur) were used to make top hats, which were very popular in Europe and North America during the 1800s. Beaver populations were also stressed due to habitat destruction as more and more wetlands were drained to create farms.

Back From the Brink: Protecting the American Beaver

Fortunately, people realized beaver populations were declining fast. They began to take conservation action to protect the species. Beaver populations have now recovered to a stable level.  However, experts say that today’s American beaver population is only 5% of what it was when Europeans’ first settled in North America.  Perhaps with continued protection of their wetland habitat, these amazing builders will be around for many years to come.

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