Biogeography of the Mountain Beaver (Aplodontia
by Daria Schwarzschild, student in
Geography 316 Fall 2003
Thank you for visiting
our site. This web page was written by a student in Geography 316: Biogeography
and edited by the instructor, Barbara Holzman, PhD. All photos and maps
are posted with specific copyright permission for the express use of education
on these web pages. The students have tried to be as accurate as possible with
the information provided and sources and references are cited at the end of each
Suborder: Sciuromorpha (squirrel-like rodents)
credit: Dan Plute, see citation
under Steele, Dale 2003|
Description of Species
Resembling a giant pocket gopher, Mountain Beaver
has a heavy body, short
limbs and dense fur ranging from grey-brown to reddish-black depending on their
particular subspecies. Their color is unvaried, except for a small white spot
below each ear. They have short furry tails with small eyes and ears, and long
vibrissae (stiff hairs located around the nose area).
Their paws have five long
slender digits that enable them to grasp as well as dig. Like all rodents, the
incisor teeth have open roots (like the molars) and grow throughout life (Nowak
and Paradiso 1983). Mountain beavers have been observed making shrill
vocalizations and grating noises.
The mountain beaver, also known as sewellel (Parker 1990) has seven subspecies
and is the only member of the Aplodontidae family. This family name comes from
the Greek aploos (simple) and odontos (tooth). It describes the
simple structure of the almost circular, always regrowing molars.
The origin of its common name is still unknown, but these mammals are
neither behaviorally nor genetically related to the beaver (Wilson and Ruff
Mountain beavers engineer and construct ingenious tunnel systems with multiple living
They use their forefeet
to dig (the incisors are also used) and then use their head and shoulders to push the soil to the entrance, kicking it
out with their hind feet.
The tunnels leading in and out from the rooms and the outside are about 4-8" in
diameter and there is an average of ten exit locations (Parker and Wood 1990). The typical lodge of the mountain beaver contains a central living
space and four additional "rooms" for food storage and droppings. The central
room is approximately 20" wide x 14" high and is filled with plant
material. The food storage area is about the same size, but the numerous rooms
for droppings are usually smaller (Parker and Wood 1990). The storage of plant
materials and droppings, and the subterranean location, create cool and very
stable temperature and moisture conditions.
Mountain beavers are herbivorous animals. They eat a variety of plants, shrubs,
ferns and tree materials depending on their location and time of year. They have
a preference for ferns and sprouts of hard woods, but at times also consume
small trunks of Douglas and Red Fir. These foods are low in calories and about
75% of daytime activity is spent in search of food (Steele and Litman 1998).
They have a large appendix that, along with the stomach, is able to store
quantities of food up to 50% of their body weight (Parker and Wood, 1990).
Mostly at night, they consume large quantities of water and food and they
eliminate one third of their body weight in urine each day (Sleeper 1997).
Often, their subterranean dwellings are designed to open directly into well
stocked plant (food) sources so they do not have to venture very far from home.
This convenience allows them to stay within the vicinity of the lodge during
their relatively long life spans (Parker and Wood 1990).
Because mountain beavers live about 4 feet under ground, they are able to
survive land clearings and forest fires. This probably also helps them avoid
Interestingly, mountain beaver also eat their own fecal pellets. This behavior
is also found among some other species. With mountain beavers, as the pellets come out of their
body, the animal catches each one and then separates them into piles of hard and
soft pieces. The hard ones are tossed into a compost area along with other
discarded plant materials. The soft ones are collected in another pile to be
stored and eaten when needed. The reason for this practice of reingestion of the
soft feces appears to be that the plant material is not fully digested the
first time through, so it is consumed again to extract remaining nutrients
These animals reproduce slowly. The breeding season is short,
approximately in February and ending in early April. The gestation period is about 28-30 days
with a litter size of usually two or three. Lactation lasts about eight weeks,
at which time the young are able to leave the nest and are almost half grown
(Nowak and Paradiso 1983). If they can survive their first year of life, mountain
beavers can live up to six years, which is quite long for rodents.
Mountain beavers are fossorial (diggers) and primarily (but not strictly)
nocturnal. Unable to sweat or pant, the Mountain beaver has no thermoregulating
mechanism, which is why they must spend most of their time in the cool moist
underground. Because of this, they are sensitive to sunlight and higher
temperatures upon leaving the burrow. In order to cool down if one does get too
warm, it spontaneously sprawls out on the ground until its body temperature
normalizes (Steele and Litman 1998). This behavior makes them vulnerable to
predators. Some of the known predators of mountain beaver are bobcats, mink,
weasels and coyote (Sleeper 1997).
beavers are capable of climbing and swimming, but in general, do not venture far from their
lodges (Wilson and Ruff 1999). Their sight and hearing is said to be
poor due to their small eyes and ears, but apparently have very acute olfactory
and tactile senses (Wilson and Ruff 1999).
During territorial encounters with other animals, the Mountain beaver will
sometimes freeze and produce a unique white secretion from glands near its eyes.
The substance possibly causes the animal to become motionless in order to avoid
attacking or it could be a chemical message to the threatening animal to stay
away (Steele and Litman 1998).
is the only species and genus in its family with no known
living relatives. The species, "is considered the most primitive living rodent,
with an ancestry that goes back into the first half of the Tertiary Period
(approximately 66 to 3 million years ago), when
modern mammals first evolved" (Wilson and Ruff 1999). There is general
agreement among scientists that 99.9 percent of all species that once inhabited
earth have become extinct because most only survive somewhere between one and
ten million years (Drew 2003). The order Rodentia has been said to have evolved
from the late Paleocene epoch (approximately 65 to 54 million years ago).
Considering these data, mountain beavers' forty
million year evolution is unusual and gives them a somewhat special status.
special rodent species, although confusingly misnamed, has existed longer than all
other living rodents and is considered by some to be a living fossil (Drew
2003). Aplondontia rufa belongs to one of three suborders of the order
Rodentia, called Sciuromorpha - squirrel-like rodents. The other two suborders
of rodents are Myomorpha - ratlike rodents and Hystricomorpha - procupinelike
rodents (Nowak and Paradiso 1983).
Phylogenic tree of the rodent family (excluding caviomorphs)
credit: Nowak and Paradiso 1983
CSU Stanislas, Endangered Species Recovery Program. 2003
||photo credit: Dan Plute, see citation
under Steele, Dale 2003
The genus, Aplodontia,
is thought to have originated in western North America since the Pleistocene era
(Parker and Wood 1990). Other members of this genus extended into forest areas
of Big Basin during the Miocene and
Pliocene time periods. It is thought that some then migrated to Eurasia towards
the end of the Oligocene period. There have been fossil records indicating that
mountain beaver once roamed in Mongolia. (Sleeper, 1997) Due to world climate
change resulting in dryer and warmer temperatures by the end of the Pliocene
era, it is postulated that all the relatives of the mountain beaver went
extinct. (Parker and Wood 1990)
Mountain beavers are confined to areas with moderate climate, abundant rainfall
and dense vegetation within Northwestern United States. This habitat extends
from southern British Columbia to coastal central California, and includes areas
in the Cascade and Sierra Nevada mountain ranges of northern and eastern
California. This mammal is common in areas with lush vegetation and succulent
plants. It can survive in up to 7000 ft. elevations, but prefer altitudes with
moderate (as opposed to alpine) climates. (Parker and Wood 1990) These animals
can not acclimate to large variations in temperature due to their inability to
physiologically regulate body temperature. Too much atmospheric heat will kill
them and they are also easily susceptible to hypothermia with too much cold
(Sleeper 1997). Another reason for their sensitivity to temperature variation is
that their kidneys can not conserve water. This is why they must have access to
water, moist environments and hydrating plant materials in order to survive.
Unfortunately, there are some subspecies of mountain beaver that are currently
on the federal endangered species list and others that are at risk. This is due
to the elimination of their habitat from human impacts such as land development,
poisoning, trappings, etc. (Steele and Litman 1998).
An interesting characteristic of the mountain
beaver is its role as a specific host for another special organism. In the
article, “Coextinction,” the Flea News indicates that one of the largest and
most ancient flea species, Hystrichopsylla schefferi, is associated with one of
the most ancient rodent species – mountain beaver. The article states that
“these strongly host-specific species may become the first fleas to be placed on
the Endangered Species list since at least two species of A. rufa are seriously
threatened by habitat reduction due to housing developments and other types of
construction.” (Flea News 1994) This particular flea, whose females can be
more than one centimeter long, may suggest an important evolutionary
relationship that would be lost if the mountain beaver were to become extinct
(Flea News 1994).
It has also been documented historically that
Native Americans at times ate mountain beaver and Northwest Coast tribes used
their skins for robes and blankets (Wilson and Ruff 1999).
CSU Stanislas, Endangered Species Recovery Program. 2003.
Available: [November 2, 2003].
Drew, Lisa W. Oct/Nov 2003. “Creatures
That Time Forgot.” National Wildlife Federation. [Online].
Available: [October 1, 2003 ].
Environment Canada. 2003. “Species
at Risk-Mountain Beaver.” Canadian Wildlife Service. [Online].
Available: [October 28, 2003]
Flea News. Vol. 49 p. 566-567. 1994. “Coextinction”
Iowa State University, Ames. Department of Entomology. [Online].
Available: [November 12, 2003]
Government of British Columbia,
Ministry of Water, Land and Air Protection. 2003. “Red Listed Species in the
Lower Mainland Region. [Online].
Available: [November 1, 2003].
Nowak, Ronald and John L. Paradiso. 1983.
“Walker’s Mammals of the World–Volume 1 (4th Edition).” Johns
Hopkins University Press. Baltimore.
Parker, Sybil P. (Editor). Wood, Charles E.
(on Mountain Beavers). 1990. “Grzimek’s Encyclopedia of Mammals – Volume 3.”
McGraw-Hill Publishing Company. New York.
Sleeper, Barbara. 1997. “Mountain
Beavers-Tracking 40-Million-Year-Old Vegetarians.” California Wild. [Online].
Available: [October 3, 2003]
Steele, Dale T. and Laurie Litman. 1998.
“Recovery Plan for the Point Arena Mountain Beaver, Aplodontia Rufa Nigra (Rafinesque).”
Region 1, U.S. Fish and Wildlife Service. Portland.
Steele, Dale. 2003. Photo.
“Mountain Beaver Journal.” [Online].
Available: [October 13, 2003]
Wilson, Don E. and Sue Ruff (Editors).
1999. “The Smithsonian Book of North American Mammals.” Smithsonian
Institution Press in Association with the American Society of Mammalogists.
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