Beavers are most active at night. They feed mostly on the inner bark of hardwood trees that grow near lakes and streams. The animals usually live in family groups called colonies. These typically consist of 12 beavers (often a pair and their last two litters), in several homes.

The beaver's home, or lodge, is built in the water or on the bank of a pond, lake, or stream. The lodge is a hollow mound of sticks plastered together with mud. The room inside, which serves as living quarters for the family, is above water level and has an air hole in the top. The lodge has thick walls that protect the animals from weather as well as from enemies. Its entrance is a tunnel that opens under water. Some beavers store twigs and branches for winter food in a second room dug under the first. Others store their food in an underwater pile near the entrance to the lodge.

Beavers dam streams and ponds to keep the water deep around their lodges at all seasons of the year. The entire colony works on these dams, the largest of which are sometimes 1,000 feet (300 m) long and more than 10 feet (3 m) high. The animals use their sharp teeth to cut down trees and shape the logs. The pieces are then dragged into the stream and laid in layers in the mud, which anchors them. Mud, stones, and branches are packed among the logs. As the dam raises the water level, more material is added at the top.

A beaver dam is a wall of sticks and stones in a stream. The dam traps water flowing downstream. Behind the dam, a pond forms. The pond is still and deep—the perfect place for a beaver home. The pond is also a place to store food and to hide from enemies.

Building a dam keeps beavers very busy. Often a whole family works together to build the dam. The beavers begin by pushing rows of sticks into the stream bed. Then they pile rocks and mud onto the sticks to weigh them down. Later, the beavers push tree branches and grass between the sticks. They add more mud so that water cannot flow through the sticks.

It usually takes two to three days for beavers to build a dam. When it is finished, the wall of sticks is high. The top of the dam rises above the water. Beaver dams can be very long, too. Most stretch between 16 and 96 feet (5 and 30 meters) across.

A lodge is a home that beavers build in a pond. The lodge is made from the same materials as the dam—sticks, rocks, and mud. The top of the lodge rises 3 to 6 feet (91 to 180 centimeters) above the water. It has a shape like a cone and looks a little like a tepee.

The lodge has several underwater tunnels and entrances. All of them lead to a main indoor room, or chamber. The chamber floor is 4 to 6 inches (10 to 15 centimeters) above the water. The chamber keeps baby beavers warm and dry. It is also a place where parents dry off after bringing food to their babies.

Beavers take good care of their lodge. They add to it and fix it often. Some beaver lodges last as long as 30 years.

Beavers mate for life. A litter consists of up to eight young, or kits, which weigh less than one pound (450 g) at birth. The young remain with the parents until they are nearly two years old and are carefully trained to take care of themselves. In their natural environment, beavers live 10 to 12 years; in captivity, sometimes nearly 20 years.

At birth, baby beavers look just like their parents, only smaller. Baby beavers are called kits or pups. Newborn kits are about 15 inches (38 centimeters) long from their heads to the ends of their tails. They each weigh 1/2 to 1 1/2 pounds (0.2 to 0.7 kilograms). Beaver kits have thick fur, sharp teeth, and open eyes. They can see, hear, walk, and swim immediately.

Before baby beavers are born, the other family members get the lodge ready. They work closely together to do this.

The mother carries her babies inside her body for three months before giving birth. She has two to four babies at a time. Usually they are born in April or May.

Like all mammals, baby beavers drink only their mother’s milk at first. They swim for the first time inside the lodge. They’re too young to waterproof their own fur, so their mother does it for them.

After one month, the kits can leave the lodge. The mother shows them how to find food and escape from enemies. The kits learn by doing what she does.

As kits grow, they play together. They wrestle and chase each other. They also dive and swim. All this exercise helps make their muscles stronger.

After one year, the young beavers are ready to start working. They cut down trees and help build and fix the dam and lodge. They also help their parents care for their newest brothers and sisters.

Young beavers live at home for about two years. Then they must go off on their own. In time, they each find a mate and build a new lodge.