Biogeography of the Mountain Beaver (Aplodontia rufa)
 
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 page.

Species Name:  Aplodontia rufa 

Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Rodentia         Suborder: Sciuromorpha (squirrel-like rodents) Family: Aplodontidae Genus: Aplodontia Species:   Aplodontia rufa
	photo 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.

 Natural History 

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 1999).

Mountain beavers engineer and construct ingenious tunnel systems with multiple living chambers. 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 predators.

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 (Sleeper 1997).

These animals reproduce slowly. The breeding season is short, starting 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).

Mountain 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). 

Evolution

Aplodontia rufa 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.

This 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

 

graphic credit: CSU Stanislas, Endangered Species Recovery Program. 2003	photo credit:  Dan Plute, see citation under Steele, Dale 2003

Distribution

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).  
 

Interesting Facts

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).

Bibliography

CSU Stanislas, Endangered Species Recovery Program. 2003. Photo. [Online]. http://arnica.csustan.edu/esrpp/aplorufa.gif.  Available: [November 2, 2003].     

Drew, Lisa W.  Oct/Nov 2003.  “Creatures That Time Forgot.” National Wildlife Federation. [Online].  http://www.nwf.org/nationalwildlife/article.cfm?articleId=500. Available: [October 1, 2003 ].

Environment Canada. 2003. “Species at Risk-Mountain Beaver.” Canadian Wildlife Service. [Online]. http://www.speciesatrisk.gc.ca/search/speciesDetails_e.cfm?SpeciesID=333. Available: [October 28, 2003]

Government of British Columbia, Ministry of Water, Land and Air Protection. 2003.  “Red Listed Species in the Lower Mainland Region. [Online]. http://wlapwww.gov.bc.ca/sry/fwh/wildlife/red.htm. Available:  [November 1, 2003].

Sleeper, Barbara.  1997.  “Mountain Beavers-Tracking 40-Million-Year-Old Vegetarians.” California Wild.  [Online]. http://www.calacademy.org/calwild/fall97/html/beavers.htm. Available: [October 3, 2003]

Steele, Dale. 2003. Photo. “Mountain Beaver Journal.” [Online]. http://www.infowright.com/mtbeaver/closeencounter.html 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.  Washington, DC.

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