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 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 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 wetland habitats.
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 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!
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.
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.
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, 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
©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
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.