The Mountain Beaver is not a mountain version of the Beaver who makes dams. They are different animals. Mountain Beavers are stocky burrowing mammals typically between 10 and 18 inches long and weighing from 1 to 3 pounds. Their fur is dark brown and they have rounded heads with small beady eyes and small ears. Their legs are short but strong and they have long, strong claws for digging on the front feet.
Mountain Beavers are powerful diggers, and they build extensive burrow systems with multiple entrances, typically in moist forest bottomlands near streams. They are solitary animals and will defend their burrows from invaders with shrill whistle-like vocalizations and grating of their large incisors.
An herbivore, the Mountain Beaver feeds on a variety of plants but prefers Sword and Bracken Fern and the cambium (green, living layer below the bark) of both coniferous and hardwood trees. They are also partial to flower bulbs, tree seedlings and newly sprouted garden plants if the opportunity arises. Food items are usually cut and dragged back to the burrow to be consumed. Mountain Beavers have poor hearing and even worse eyesight, but they have well-developed senses of smell and touch.
Although they are common in Western Washington, Mountain Beavers are seldom seen due to their secretive habits. They are predominantly nocturnal, but are occasionally active during the day.
Female Mountain Beavers begin breeding at 2 years old. Mating takes place in late winter and 3-5 young are born in the spring. The young stay with their mother throughout the summer but by autumn they are weaned and set off to establish their own burrows/territories.
If you live near a moist, forested slope or ravine in Western Washington, there is a good chance that you have Mountain Beavers in your area. Most conflicts that arise between property owners and Mountain Beavers involve the animals burrowing in undesired areas or eating ornamental or garden plants. There are many ways to address conflicts with Mountain Beavers, but exclusion is the most effective way to mitigate the problem in most cases.
To prevent Mountain Beavers from damaging the trunk or branches of young trees, a piece of stovepipe, PVC or sheet metal can be used to encircle the lower trunk. The barrier should be at least 18 inches tall to prevent the animals from climbing over it, and it should be secured in such a way that it can easily be loosened or removed as the tree grows.
Mountain Beavers seem to have a strong affinity for rhododendrons and similar ornamental shrubs. Small, loose wire fencing can be used to prevent Mountain Beavers from accessing these plants. The fence can be constructed using chicken wire, or a similar 1-inch mesh wire or heavy plastic attached to metal or wooden stakes. It should be at least 2 feet high, and it should not be pulled tight between the stakes. If the Mountain Beaver does try to climb the fence, the laxity in the wire mesh will make it much more difficult.
It is also a good idea to build the fence with a slight outward angle (away from the plants) to make it more difficult to climb. A two-foot skirt running along the ground on the outer side of the fence and staked down at the ends will also prevent Mountain Beavers from digging underneath.
It is possible to exclude Mountain Beavers from your yard entirely with a fence like the one described above. It is easiest to do if your yard is bordered on both sides by solid fencing. You simply build the small wire fence between your yard and the Mountain Beaver's burrow system and secure to the solid fencing at either end. If your yard already has a traditional wooden or chain-link fence, you can affix the wire or sturdy plastic mesh directly to the existing fencing and extend the 2-foot horizontal skirt directly out from the bottom of it to prevent the Mountain Beavers from digging in.
Simply allowing Mountain Beavers to use your property may be the most desirable course of action. They are interesting, uniquely Northwestern mammals that few people even know exist. If you are fortunate enough to catch a glimpse of these curious little animals as they go about the business of their lives, you may find that they are a welcome addition to the diversity of life in your neighborhood.
Above: A young Mountain Beaver in care at PAWS Wildlife Center