I have indeavoured in many instances to make the indians sensible how anxious I was to obtain one of these animals entire, without being skined, and offered them considerable rewards to furnish me with one, but have not been able to make them comprehend me – Meriwether Lewis
No, no, this is not the industrious beaver you are familiar with – the one that chews down trees, builds dams, and has a large flat tail. This rodent (both are in the same Order – Rodentia) is much smaller and seldom seen, though his handiwork can be quite evident in back yards. Lloyd in our Seattle office has become quite familiar with the species as he has a running battle with one – similar to Bill Murray’s efforts with a gopher in Caddy Shack. More on that later.
Mountain beavers are small, averaging 12-20 inches in length and weighing about 35 ounces or so. They are brown to reddish brown with short tails and large claws. As will all rodents, their four incisors are constantly growing and their length is only controlled by gnawing. And yes, for some reason teeth can get out of control and grow outlandishly long, affecting feeding – or in rare instances can grow through opposite side of the skull, which needless to say, can be a problem.
Mountain beavers are the only member of their family (Aplodontiidae) and their Genus. They are considered the most primitive rodent alive due to a number of tooth and skull morphology characteristics. Genetic work indicates their closest relatives are squirrels, but they split off the evolutionary tree from this group 55 to 35 million years ago. Interestingly, the earliest indication of them in North America is in the late Pleistocene – so “only” about a million years ago.
Aplodontia – “simple tooth”, refers to how the cheek teeth are nestled in a basin, and rufa – red or reddish, a reference to their fur color.
They range through western Washington and Oregon up to tree line and into northern California and down the spine of the northern Sierra. They don’t hibernate and build deep and complex tunnel systems. In higher elevations they will remain active beneath the snow pack – but they don’t thermo-regulate as well as other rodents and spend much of their time underground.
They eat a wide variety of plants including the above and below ground parts. Their diet includes ferns, salal, nettles, fireweed, bleeding heart, salmonberry, dogwood, rhododendrons and most anything you plant in your backyard. Their thumbs are slightly opposable and they will sit on their back legs and much away on their plant meal. Because they have very inefficient kidneys they must drink about 1/3 of their body weight in water every day – so a close water source is important. Mountain beavers are generally solitary, except during the breeding season, and are territorial.
Breeding occurs in February through April and two to four young are born following a 28-30 day gestation. They exhibit coprophagy (yes – there is a name for this) and eat their soft fecal pellets to extract undigested nutrients (rabbits do this as well)– hard fecal pellets that have gone through the digestive system twice are stored in a special “toilet” area in the underground burrow. Thus you will never see mountain beaver pellets above ground. There are lots of animals that prey upon mountain beavers including bobcats, cougars, coyotes, foxes, golden eagles, owls, and others.
Mountain beavers also have another distinctive trait – they are the host for the world’s largest flea Hystrichopsylla schefferi – females of this species can be up to 0.3 inches long. Luckily they don’t seem to like domestic pets as a host! Lewis and Clark encounter the critter – or at least cloaks made of their fur by the Chinook Indians and traded at Fort Clatsop. When questioning them about the animal they were told it was a She-wal-lal, which got transcribed as Sewellel. Only later did others determine that Clark mistakenly took the name to represent the animal, while the Chinook were referring to the name of the cloak.
It can be the bane of the gardener – once they set up house the can wreak havoc by munching on anything available. I had a friend who tried the usual suggestions – soaking rags in coyote urine (yes –shop online for this!) and stuff them in the borrow holes, pour used cat litter down the holes, cover up holes – but none of this did the trick. But after about two weeks of baiting a live trap with apples the critter was captured – spent the winter in the basement of a neighbor’s house, and was released far away in the spring. Lewis and Clark asked the Chinook to bring them a live one – but that did not happen.
I’ve seen only two – one in Discovery Park in Seattle, and the second while hiking a switchback in the Cascades. I just happened to look up and saw this guy sitting on a log about 6 feet away, casually munching on a snack. Hopefully Lloyd will capture his nemesis soon and we can get a picture of that one.
The animal also is known as a Boomer, which is the mascot of a Portland minor league baseball team – and isn’t there a PNW college with the mountain beaver as its mascot? Keep your eyes open for burrows, while hiking or while walking around your neighborhood.