mountain beaver
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What is a mountain beaver?
The mountain beaver (Aplodontia rufa) is a unique, muskrat-sized burrowing rodent native to the Pacific Northwest of North America. It is characterized by its extremely short tail, small rounded ears, and short limbs, and typically weighs less than 2 kg.
These solitary animals possess strong senses of touch and smell but have limited sight and hearing. Mountain beavers construct extensive tunnel systems with nest sites and food storage. They do not hibernate, remaining active in winter through tunnels in the snow. Their diet includes ferns, leaves, bark, and seedlings, with a preference for wet forests and meadows near streams.
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Where do mountain beavers live?
The mountain beaver, Aplodontia rufa, is a unique, muskrat-sized rodent native to the Pacific Northwest of North America. They are not closely related to beavers. Instead, they are more closely related to squirrels.
These solitary animals reside in disjunct regions from British Columbia to California, including the Sierra Nevada mountains and areas north of San Francisco Bay. They thrive in wet forests and meadows below the treeline, favoring areas near streams with thick undergrowth. Mountain beavers are good swimmers and construct complex tunnel systems with nest sites, food storage, and multiple surface openings. Though active day and night, they remain close to their burrows.
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What do mountain beavers eat?
Mountain beavers, native to the Pacific Northwest, have a diet that changes throughout the year. During the summer, they consume various ferns and leaves from shrubs and deciduous trees. In the winter, they switch to bark, conifer seedlings, and deciduous trees. They also eat plants that are toxic or unpalatable to other animals, such as bracken fern, devil’s club, stinging nettle, and rhododendron. Mountain beavers occasionally climb trees to chew off twigs, and they store vegetation near their burrow entrances to dry for later consumption or use as nest lining.
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How do mountain beavers build their homes?
Mountain beavers, unlike the American and Eurasian beavers, do not build dams. They are burrowing rodents that create extensive tunnel systems with nest sites, food-storage chambers, and multiple surface openings. These tunnels, which are 13–18 cm high and 15–25 cm wide, are mainly constructed during the summer. Mountain beavers pile vegetation near burrow entrances to dry it before storing it inside for food or nest lining. These solitary animals dwell in wet forests and meadows, especially near streams, and are good swimmers.
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How are mountain beavers different from regular beavers?
The mountain beaver (Aplodontia rufa) is a unique rodent found in the Pacific Northwest, distinct from the common American and Eurasian beavers (genus Castor).
| Feature | Mountain Beaver | Regular Beaver |
| --- | --- | --- |
| Size and appearance | Smaller, about 1.6 feet long and 4.4 pounds, with an extremely short tail| Larger, up to 31 inches long and 35-66 pounds, with a distinctive flat, paddle-shaped tail|
| Habitat | Wet forests and meadows near streams, constructing extensive burrow systems| Streams, rivers, marshes, and ponds, constructing dams and lodges|
| Social Behavior | Solitary| Colonial, living in family groups|Unlike regular beavers, mountain beavers do not build dams. They are good swimmers and construct tunnels for shelter and food storage. Mountain beavers have limited vocalizations, mainly soft whining or grating sounds. They eat ferns, leaves, bark, and seedlings, and sometimes climb trees to chew off twigs.
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Why are mountain beavers important to their ecosystem?
Mountain beavers are vital to their ecosystems because they create habitats for various species by burrowing and altering vegetation. Their tunnels provide shelter and nesting sites for other animals, while their consumption of specific plants, including those toxic to other species, shapes plant communities. They are good swimmers and prefer areas near seeps and streams in the understories of brambly thickets. As the sole surviving species of an ancient lineage, they represent a unique evolutionary history, making their preservation important for maintaining biodiversity.
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mountain beaver, (Aplodontia rufa), a muskrat-sized burrowing rodent found only in the Pacific Northwest of North America. Unlike the American and Eurasian beavers (genus Castor), the mountain beaver has an extremely short tail and is less than a half metre (1.6 feet) in length; weight is less than 2 kg (4.4 pounds).
It is characterized by small rounded ears, small eyes, short and robust limbs with five digits on each foot, and a white spot under the ears. All digits except the thumb (pollex) end in long, curved, sharp claws; the thumb is partially opposable and bears a nail. The animal is dark grayish to reddish brown on the upperparts and gray beneath, its short coat composed of a dense underfur with scattered guard hairs. Mountain beavers are solitary and have acute tactile and olfactory senses but limited ability to see and hear. Their vocalizations are limited to a soft whining, sobbing sound when in pain, grating produced by the teeth, and a high squeal when fighting.
The range of the mountain beaver consists of four disjunct regions: one extending from southern British Columbia to the northern tip of California, another at Mount Shasta and along the western slopes of the Sierra Nevada mountains, and two tiny populations north of San Francisco Bay along the California coast. Here they live in wet forests and meadows at all elevations below the treeline wherever the soil is deep. They are good swimmers and especially prefer areas near seeps and streams in the understories of brambly thickets. Although active night and day, mountain beavers are rarely found far from the entrances of their extensive burrow systems. They construct tunnels 13–18 cm (5–7 inches) high and 15–25 cm wide that radiate from nest sites, food-storage chambers, and numerous openings to the surface. Most burrowing occurs during the summer months, and aboveground activity nearly ceases in winter. However, the mountain beaver does not hibernate and travels through burrows made in the snow. Mating occurs during this time, with a usual litter of two or three kits appearing from February to April after about one month’s gestation. During summer, mountain beavers eat most species of ferns along with leaves of shrubs and deciduous trees, then shift to bark and seedlings of conifers and deciduous trees. Also eaten are bracken fern, devil’s club, stinging nettle, and rhododendron, which are toxic or unpalatable to other animals. Occasionally mountain beavers climb trees, where they will chew off twigs up to six metres from the ground. In August, mountain beavers pile vegetation near burrow entrances until it becomes wilted or dry, then move it into the burrow to be eaten or used as nest lining.
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Aplodontia rufa is the sole remaining species of the family Aplodontidae (suborder Sciuromorpha, order Rodentia). It is relict from a diverse evolutionary history (three families and 34 genera) extending back to the Eocene Epoch (55.8 million to 33.9 million years ago) of North America; some now-extinct forms also lived during Oligocene to Miocene times in Europe and Asia. Fossils of the living species come from Late Pleistocene sediments in northern California, within its modern range. The mountain beaver is more closely related to squirrels (family Sciuridae) than to beavers (family Castoridae) or any other living rodent.