Oregon Symbols, Animal: Beaver

Adopted in 1969.

The American Beaver (Castor canadensis) was named Oregon state animal by the 1969 Legislature. Prized for its fur, the beaver was overtrapped by early settlers and eliminated from much of its original range. Through proper management and partial protection, the beaver has been reestablished in watercourses throughout the state and remains an important economic asset. The beaver has been referred to as "nature's engineer," and its dam-building activities are important to natural water flow and erosion control. Oregon is known as the "Beaver State" and Oregon State University's athletic teams are called the "Beavers."

Physical Characteristics

The beaver is a large, semi-aquatic rodent with a large, flattened tail. Beavers are about 3 ft (0.9 m) long; their flat, thick tail is about 1 ft (30 cm) long. They weigh 30-70 pounds (14-32 kg). Like all rodents, their teeth continue to grow their entire lives. Their ears and nostrils can close while the beaver is underwater. While swimming, transparent eyelids protect their eyes. Beavers can close their mouth by closing a flap located behind their teeth, allowing them to chew while holding their breath. It is a strong swimmer and can swim up to 5 miles per hour (8 kph). The beaver can swim underwater for up to 15 minutes. Young beavers are called kits. Beavers live in forests in North America and in parts of Europe and Asia. Beavers do not hibernate over winter, but they will stay in their lodge, where they have stored enough food to last until spring.

Natural History

Diet

Beavers are herbivores (plant-eaters). They eat tree bark, leaves, roots, twigs, and water plants. Their favorites include willow, maple, poplar, beech, birch, alder, and aspen trees. They also eat water vegetation as well as buds and roots. Cellulose, which usually can not be digested by mammals, is a major component of their diet. Beavers have microorganisms in their cecum (a sac between the large and small intestine) that digest this material.

Reproduction

Female beavers are sexually mature at 2.5 years old. They give birth to one litter of kits per year, usually between April and July. The gestation period is about 3 months. The litter usually consists of 4 kits, but up to 8 are possible. They are born with all of their fur, their eyes open, and their incisor teeth erupted.

The young usually stay with their parents for 1-2 years and then leave to make their own homes.

(Frazier, 1996; Sevilleta LTER, 1995)

Predators

The beaver is hunted by many animals, including coyotes, wolves, bears, lynxes, and wolverines. Minks, owls and hawks prey upon young beavers. Beavers cannot move very quickly on land, so their best defense from predators is to retreat into the water and go into their lodge.

 Lodges and Dams

Beavers build sophisticated lodges out of sticks and mud. The dome-shaped lodge is built in water and only has underwater entrances. If the local pond water isn't deep enough, the beaver will build a dam (or a series of dams) downstream from where the beaver wants to build a lodge. The dam forms a deep pond. Beavers cut down trees for the dam using their strong teeth. The water in the pond must be deep enough so that the pond bottom won't freeze in winter, blocking the lodge's entrance.

Behavior

Beavers form monogamous pairs and usually live in family groups of up to 8 related individuals called colonies. The younger siblings stay with their parents for up to 2 years, helping with infant care, food collection, and dam building.

Beaver families are territorial and defend against other families. In order to warn each other of danger, beavers slap their tails against the water, creating a powerful noise.

Beavers are primarily nocturnal. They are only occasionally seen during the day. They usually wake at dusk.

Beavers travel good distances from their homes to find food. If they find a good source, they build canals to the food source as a way to float the food back to their lodges. Logs and twigs are stored underwater for winter feeding.

(Hall and Kelson, 1959; Frazier, 1996; Sevilleta LTER, 1995)