Crawlies with Cri: Mountain beaver

Mountain beaver Aplodontia rufa, temperate rain forest, British Columbia, Canada

This week we’re introducing you to a bonus PNW critter outside of Crawlies. First, because these critters are super cool; second, because Crawlies is all about critters I’ve personally met, and this featured critter is elusive, to say the least.
Let’s get to know Oregon’s least seen mammals – the mountain beaver (Aplodontia rufa). They do not exclusively live in the mountains; they can even be found at sea level. Moreover, they are not beavers (Castor canadensis). They aren’t even closely related to beavers. How did they get that confusing moniker?
They sometimes chew down saplings for the bark. That’s it. That’s as close as they get to beavers – semi-beaver behavior.
So, we know what they aren’t. What are they? They are the only animal in their genus (Aplodontia). They are rodents, and they are ancient. They date back to the Miocene geologic era, ranging from 5-25 million years ago. Many taxonomists consider them to be the most primitive living rodent species.
At 10 – 12 inches in length, mountain beavers are about “muskrat size” but have teeny tails, less than one-half inch. They’ve been described as resembling “overgrown hamsters” or “tailless muskrats.”
Fun fact: They used to be closer to “actual hamster” size; over the eons their size has doubled.
They are endemic to the Pacific Northwest, but most people don’t even know they exist, let alone that they have existed for ages.
This goes back to their elusive nature. They live in two different regions: British Columbia to Humboldt County, Calif. and Mt. Shasta, Calif. to Western Nevada.
In Oregon they are considered “common if seldom seen.” Why is that? Mountain beavers are asocial animals who live in burrows alongside rivers, creeks, streams and other water sources. They rarely leave their burrows, except to gather food, and even then, they only travel short distances and most likely only come out at night.
Mountain beavers are herbivores, dining on a variety of plants such as nettles, dogwood vegetation, brambles, fireweed and salmonberry. They also eat bracken ferns that are poisonous to other animals.
Mountain beavers don’t just prefer to be near water; they have to be near water. Their kidneys cannot concentrate urine, so they need to drink up to two-thirds of their body weight in water every single day.
As for their living situation, their tunnels are quite organized, with multiple entrances and separate rooms for nesting, storing food, toilet and holding “earth balls”. No, not fancy dance parties, but rocks or hard clay that are believed to serve as plugs within their tunnel systems and upon which mountain beavers sharpen their incisors.
Mountain beavers have poor eyesight and hearing, but excellent senses of smell and touch. They have what they need for their secretive tunnel and night life. You don’t stick around for millennia if you aren’t excellently equipped for survival.
Final fun facts: Mountain beavers can climb trees and swim short distances. They don’t hibernate, so are active year-round. They can issue a squeal or sharp whistle to defend their burrows. They have two or three young each spring, and once grown, those offspring head out to find their own territories.