Mountain Beavers

Lewis’s Description

That “small animal about the size of a squirrel” with the fur of which Lewis wished his “Tiger Cat” capote to be lined, may have been the one that he soon learned was locally called a sewelel. At Fort Clatsop on 26 February 1806, he wrote the following comments on this “new” species of mammal:

Sewelel [suh-WELL-ul] is the Chinnook and Clatsop name for a small animal found in the timbered country on this coast.    the natives make great use of the skins of this animal in forming their robes, which they dress with the fur on them and attatch together with sinews of the Elk or deer. I have never seen the animal and can therefore discribe it only from the skin and a slight view which some of our hunters have obtained of the living animal.    the skin when dressed is from 14 to 18 inches in length and from 7 to 9 in width; the tail is always severed from the skin in forming their robes I cannot therefore say what form or length it is.    one of the men informed me that he thought it reather short and flat.    that he saw one of them run up a tree like a squirrel and that it returned and ran into a hole in the ground.    the ears are short thin pointed and covered with short fine hair.    they are of a uniform colour, a redish brown; tho’ the base of the long hairs, which exceed the fur but little in length, as well as the fur itself is of a dark colour for at least two thirds of it’s length next to the skin.    the fur and hair are very fine, short, thickly set and silky.    the ends of the fur and tips of the hair being of the redish brown that colour predominates in the ordinary appearance of the animal.I take this animal to be about the size of the barking squirrel of the Missouri.^[1]Lewis’s standard for his comparison of the sewellel with the “barking squirrel of the Missouri” or prairie dog, which he had first seen on 7 September 1804, was close; the latter … Continue reading    and beleive most probably that it is of the Mustela genus,^[2]This is one of the few times we find Lewis venturing to identify a new species in scientific terms. Understandably, he was wrong. The genus Mustela belongs to the the family Mustelidae, which … Continue reading or perhaps the brown mungo itself.^[3]Mungo was a name for the mongoose, a native of Nigeria and the Congo. The mountain beaver bears a strong resemblance to the mongoose, the most conspicuous difference being the latter’s much … Continue reading 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. I have purchased several of the robes made of these skins to line a coat which I have had made of the skins of the tiger cat.    they make a very pleasant light lining.

Elusive Rodent

Our human impulse to name everything has made an imposter of the “mountain beaver.” First–and last–it is not a beaver. It doesn’t confine itself to mountainous habitats. It doesn’t build dams on streams to create ponds, or dwell in partially subaqueous lodges made of sticks. It is a sluggard compared with the nimble and active squirrel. In dry areas it favors the proximity of small streams, but it is strictly a land animal, living in underground burrows much like the prairie dog’s. The subterranean domicile of a single A. rufa may occupy an area 100 yards in diameter. In rainy climates it shelters the entrances to its burrows with little tents of sticks covered with leaves. The mountain beaver is so attached to an underground existence that it is rarely to be seen in the light of day, and consequently is hard to capture–which might explain why the natives around Fort Clatsop seemed not to understand Lewis’s request. The only place on earth where it can ever be seen, day or night, is in the Pacific Northwest of North America.

This secretive, primitive little rodent, which somewhat resembles the woodchuck and the muskrat, belongs to the same mammalian order, Rodentia (ro-DEN-tee-uh), as the more familiar and ubiquitous flat-tailed beaver, Castor canadensis, but otherwise they have nothing in common. The order consists of 39 families, 389 genera, and 1,702 species. The so-called mountain beaver is the only species, rufa (ROO-fuh; reddish),^[4]In giving it the specific epithet rufa, Constantine Rafinesque relied on Lewis’s description of the fur as reddish brown, although it also appears as a dark brown or black. Adrian Forsyth, … Continue reading in the only genus, Aplodontia (ap-lo-DON-ti-uh), in the singular family Aplodontiidae (AP-lo-don-TEE-ih-dee). Aplo is a Latin word for simple; dontia is Latin for teeth. The sewellel must keep chewing throughout its entire 5- to 10-year life–fleshy and woody plants, principally–in order to keep its incisors from growing too long. It also grooms its teeth on “beaver baseballs”–chunks of stone or clay of about that size which it encounters in digging its dens. Its Indian name, sewellel, is said to have come from the Chinookan word swal·l, which actually refers only to a robe made of the animal’s skins.^[5]Coues’s detailed annotation on the history of the sewellel’s common and Latin names illustrates the progress of the scientific discipline of classification and nomenclature between 1806 … Continue reading

The mountain beaver is less of a show-off than its larger and more seductive cousin the genuine beaver–Castor canadensis–partly because it doesn’t have a flat tail with which to spread its alarms. In fact, it has only a stumpy vestigal tail, less than an inch and a half long on a mature male. Perhaps its best attribute has been that despite the old appeal of its pelt in Northwest-coast Indian clothing, no one else–or since–has found it to have any merchantable value.

References

The Encyclopedia of Mammals. Edited by David Macdonald. New York: Facts on File, Inc., 1984.

National Audubon Society Field Guide to North American Mammals. Edited by John O. Whitaker, Jr. Rev. ed., New York: Knopf, 1996.