Mountain Beaver

Mountain Beaver

Aplodontia, Mountain boomer, Ground bear, Giant mole, Sewellel beaver, Boomer

Aplodontia rufa
Population size
Life Span
6-10 years
g oz 
cm inch 

The Mountain beaver (Aplodontia rufa) is a rodent from North America. It should not be confused with true North American and Eurasian beavers, to which it is not closely related; instead its closest relatives are squirrels.


Mountain beavers are usually dark gray or brown, but their fur can range from slightly more reddish (rufa) to more blackish depending on subspecies, with a light patch under each ear. The animals have distinctively short tails. Their superficial similarity with true beavers reflects only their relatively large size (for rodents), strong odor, preference for living in extremely watery/moist habitats, and propensity to gnaw bark and cut branches.




Mountain beavers live in North America, their two main ranges being from Merritt in British Columbia to Rio Dell in California and from Mt. Shasta, California over to western Nevada. Sparse populations also inhabit the Californian coast. Their habitat ranges from sea level forested areas to timberline peaks. They prefer areas of second growth tree species and shrubs, and like to be near water. They are most common in high mountain peaks that have deciduous forest and least found in coniferous forests.

Mountain Beaver habitat map

Climate zones

Mountain Beaver habitat map
Mountain Beaver
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Habits and Lifestyle

Mountain beavers are not very sociable. They tend to stay within a few meters of their burrows. With their home ranges overlapping, each beaver defends its nest site. These animals are predominantly nocturnal, though they are occasionally active in the daytime. They vocalize with whistles and booming sounds and will squeal and make grinding noises with their teeth when fighting. The burrow system of these animals is centered around their nest sites. Nearly all the entrances connect to the nest chambers underground. The nest chambers are lined with dried leaves. The entrance to the tunnels either has vegetation covering it or is covered over with a tent-like stick structure. Mountain beavers do not fell trees, build dams, live in lodges, or communicate by tail slappings. They forage above the ground climbing trees a few meters high.

Group name
Seasonal behavior

Diet and Nutrition

Mountain beavers are herbivores (folivores, graminivores). Their diet includes ferns, grasses, forbs and other plants.

Mating Habits

6-8 weeks
2-3 pups
pup, kit, kitten

Little information is known about the mating system of Mountain beavers. Breeding occurs between January and March. The gestation period usually takes 6-8 weeks and the female gives birth to 2-3 young. At birth, the young weight 25.5g; they are pink, blind, helpless, and have little fur. They are able to function within 6 to 8 weeks and become reproductively mature at the age of 730 days.


Population threats

This is a common species and it is considered a pest in much of its range due to the damage it causes. People use herbicides and burning to reduce the food source for the beavers. The threats to the subspecies phaea and nigra include wildfire, expansion of exotic plants, livestock grazing, rodent control measures, housing development, alteration of stream flows, highway construction, predation by dogs and cats, and small population sizes.

Population number

According to the IUCN Red List, the total population size of the Mountain beaver is between 10,000 to more than 1,000,000 individuals. Currently, this species is classified as Least Concern (LC) on the IUCN Red List and its numbers today are stable.

Ecological niche

Mountain beavers may affect predator populations, including bobcats, coyotes, cougars, golden eagles, and owls, as items of prey.

Fun Facts for Kids

  • The senses of sight and hearing of Mountain beavers are very poor but they have well-developed senses of smell and touch.
  • Mountain beavers are excellent tree climbers and swimmers
  • Beavers are assisted in seeing underwater with a third transparent eyelid.
  • A beaver’s front teeth will never stop growing, as with all rodents.
  • A beaver's tail can be used as a rudder, a lever to drag branches, a third leg for balance when standing upright, and a sound maker to slap on water to warn fellow beavers of danger.
  • Mountain beaver burrows can be used by other species including mink, moles, voles, weasels, and salamanders.
  • Mountain beavers, like humans, have opposable thumbs.


1. Mountain Beaver Wikipedia article -
2. Mountain Beaver on The IUCN Red List site -

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