Aplodontia rufa
Silhouette: Daderot · PhyloPic
In 3 days ~20% in a week ~30%
The mountain beaver (Aplodontia rufa) or sewellel is a North American rodent. It is the only living member of its genus, Aplodontia, and family, Aplodontiidae. It should not be confused with true North American and Eurasian beavers, to which it is not closely related; the mountain beaver is instead more closely related to squirrels. There are seven subspecies of mountain beaver, six of which are found in California and three of which are endemic to the state.
The name sewellel was recorded by Lewis and Clark who misunderstood the Chinook word [ʃʔulal] (which they annotated as "she-wal-lal"), the name for garments made from their skin; the Chinook themselves call it "ogwoolal" (pronounced [əɡʷulal]). "Mountain beaver" is a misnomer as the animal is not a true beaver nor restricted to mountains.
The name Aplodontia ("simple tooth") is in reference to the single large basin comprising the bulk of each cheek tooth. The specific epithet, rufa, means red or reddish. Most references use the spelling "Aplodontidae" for the family name. This has been deemed incorrect due to the technical rules of converting a genus name into a family name. The proper conversion of Aplodontia... Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Olympic National Park | 🇺🇸 United States |
More parks will be added in future updates.
| # | City | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Seattle | 🇺🇸 United States |
With luck
About 10% of wildlife watchers report a Mountain Beaver sighting in Olympic National Park on a given day, based on 11 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the 19th most-seen of the 27 mammals we can rate there. Over three days the chance rises to about 20%, and over a week to about 30%, if each day is a fresh chance.
June and August
In those months about 10% of wildlife watchers report a Mountain Beaver in Olympic National Park on a given day, against under 5% in July and September–May, the lowest months. Those are among Olympic National Park's driest months, with about 65 mm of rain a month against 370 mm in November.
Between noon and 3 pm
Across all the parks we cover, that three-hour window holds the most Mountain Beaver sightings with a recorded time, and about 7 in 10 of them come between 6 am and 6 pm: it is a daytime animal.
Only Olympic National Park, in our data
Olympic National Park is the only park on Wallace's Line with enough records to rate Mountain Beaver sightings: about 10% of wildlife watchers there report one on a given day.
Same order: Rodentia
The closest relatives of the Mountain Beaver that you can see in Olympic National Park (order Rodentia, Rodents) are Douglas' Squirrel (about 40%), Olympic Marmot (about 40%) and Yellow-pine Chipmunk (about 30%), with each one's daily chance of a sighting.
GBIF citizen-science records
It is estimated from how often the Mountain Beaver is recorded against all the mammals logged in Olympic National Park (11 verified sightings from 2019 to 2026), calibrated against known sighting rates. Figures are rounded to the nearest 10% because citizen-science data supports honest approximations, not decimals, and months with records from fewer than five people show "—". How it works.
