Mountain Beaver

Mountain Beaver

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

Aplodontia rufa
Life Span
6-10 yrs
500-900 g
30-50 cm

The Mountain beaver is a medium-sized burrowing rodent that looks like a giant pocket gopher. It has small eyes and ears set in a distinctive triangular flattened skull. Its fur is dark brown with a pale spot below each ear. It has long whiskers, high conical cheek teeth, long claws, and a short furry tail.



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. This species is most common in high mountain peaks that have deciduous forest and least found in coniferous forests.

Mountain Beaver habitat map

Climate zones

Habits and Lifestyle

Mountain beavers are not very sociable. They tend to say within a few meters of their burrows. With their home ranges overlapping, each beaver defends its own 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.

Group name

Diet and Nutrition

Mountain beavers are herbivores and their diet includes grasses, forbs ferns like bracken fern and sword fern.

Mating Habits

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

Little information is known about the mating system of Mountain beavers. Breeding occurs from February to April and gestation usually takes six to eight weeks. Litters numbering two to three are common. At birth, beavers weight 25.5g, are pink, blind, helpless, and have little fur. They are able to function within six to eight weeks. Mountain beavers are 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

Mountain beaver is a very widespread, common species. The IUCN Red List resource estimates the global Mountain beaver population size from 10,000 to over 1,000,000 individuals. The subspecies nigra is thought to have 10 populations within its geographic range, totaling 100 animals. Currently Mountain beavers are classified as Least Concern (LC) and their numbers today remain 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.
  • Beavers hiss when they are frightened.
  • 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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