January 2022

Beavers are found throughout most of North America. 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 family members of danger, beavers slap their tails against the water, creating a powerful noise. Beavers are primarily crepuscular. They are only occasionally seen during the day. They usually wake at dusk and are also active at dawn. The tails are one of the defining characteristics of beavers. They are broad and flat with large, blackish scales. Another characteristic of beavers is their teeth. Like all rodents, beavers have large central incisors (front teeth) that are always growing. They must keep them trimmed by gnawing bark. Beavers travel good distances from their homes to find food. If they find a good source, they build canals to the food source to float the food back to their lodges. Logs and twigs are stored underwater for winter feeding. Beavers float small trees and branches through canals to the stream where they are building their lodge. The lodge can have several underwater entrances to keep out predators, with a large dry room inside that is used as a nursery and haven. The living area is well insulated by the lodge and surround-ing water, so the temperature is considerably warmer inside the lodges than outside. Beavers are generally beneficial to the environment. They are instrumental in creating habitats for many aquatic organisms, maintaining the water table at an appropriate level, and controlling flooding and erosion, all by building dams. Beavers are thickset and heavy, about 1.2 m (4 feet) long, including a 30 cm (1 foot) paddle-shaped tail; they weigh as much as 32 kg (70 pounds). Their legs are short and their hind feet large and webbed. They use their forepaws like hands. A pair of anal musk glands, or castors, produce castoreum, which is used by the beavers to waterproof the fur and is used commercially in making perfume. Dense brown to tan underfur is covered by coarse guard hairs. Chisel- like front teeth enable the beaver to gnaw down trees used for building dams, island lodges, and canals. They mate in January-February, and one to eight young are born in April-May. Beavers reach maturity in 2-3 years and live about 16 years. 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 is possible. They are born with all 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. Beavers eat bark and cambium (the softer growing tissue under the bark of trees). 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 cannot 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) to digest this material. Beavers build dams to slow down the flow of water in streams and rivers and then build stable lodges for shelter in the ponds created. The dams are engineered according to the speed of the water; in slow water the dam is built straight, but in fast water the dam is built with a curve in it. This provides stability so that the dam will not be washed away. The lodges are made of sticks, mud and rocks. In faster rivers and streams, beavers sometimes build lodges into the sides of banks. Some lodges are large enough to fit a human inside them. The conservation status differs with respect to source, but there have been significant threats to the survival of the beaver. Beavers have been hunted and trapped extensively in the past and by about 1900, the animals were almost gone in many of their original habitats. Pollution and habitat loss have also affected the survival of the beaver. In the last century, however, beavers have been successfully reintroduced to many of their former habitats.