Table of Contents
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Overview
Brief Summary
Description
Adaptation: The many similarities in the form of the skull of an early rodent from the Paleocene, Paramys, and the living Mountain Beaver, Aplodontia, suggest roughly similar functional patterns of foraging and feeding in the two.
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- Original description: Rafinesque, C.S., 1817. Descriptions of seven new genera of North American quadrupeds, p. 45. American Monthly Magazine and Critical Review, 2(1):44-46.
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Distribution
Range Description
The subspecies nigra has the most restricted distribution of all subspecies, it is known only from an area of 60 km² in the vicinity of Point Arena, Mendocino County, California. The subspecies phaea is known primarily from an area of approximately 285 km² within the Point Reyes National Seashore, Marin County, California, with a few populations occurring on privately owned land immediately adjacent to the Park.
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Geographic Range
Mountain beavers are found in North America. The two main ranges of mountain beavers are from Merritt, British Columbia to Rio Dell, California and from Mt. Shasta, California to western Nevada. There are also sparse populations of this species on the Californian coast (Carraway, 1993).
Biogeographic Regions: nearctic (Native )
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National Distribution
Canada
Origin: Native
Regularity: Regularly occurring
Currently: Present
Confidence: Confident
Type of Residency: Year-round
United States
Origin: Native
Regularity: Regularly occurring
Currently: Present
Confidence: Confident
Type of Residency: Year-round
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Global Range: (20,000-2,500,000 square km (about 8000-1,000,000 square miles)) Pacific coast of western North America, from southwestern British Columbia south to central California. From near Merritt, British Columbia, south along the Cascade, Olympic, Coast, and Siskiyou ranges to Rio Dell, California; Mt Shasta, California, southeastward through the Sierra Nevada of eastern California and west-central Nevada; Point Arena, Mendocino County, California; and near Pt. Reyes, Marin County, California (Carraway and Verts 1993).
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Physical Description
Morphology
Physical Description
Mountain beavers are dark brown except for a white spot below each ear. They have strong incisors. Their head is flat and wide and their nose is slightly arched. The body is thick, heavy, and covered with coarse, dull fur. Underneath the fur is a sparse covering of guard hair, which is dark red of grayish brown in color. They have short limbs and their total length is 300 - 470 mm (Carraway, 1993).
Average mass: 1125 g.
Average basal metabolic rate: 1.892 W.
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Size
Size in North America
Average: 354 mm
Range: 238-470 mm
Weight:
Average: 1,065 g
Range: 806-1,325 g
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Ecology
Habitat
Habitat and Ecology
A. r. nigra occurs only in sheltered gulches, steep north facing slopes, and in a few old dune systems, where it requires soil conditions that allow easy excavation and abundant succulent plant food. A. r. phaea requires north-facing slopes with dense thickets of brush typically composed of coyote brush, sword fern, blackberry, and poison oak. Openings within Bishop pine forest with dense herbaceous understorey of sword fern and blackberries are also occupied (Carraway and Verts 1999).
Mountain beavers feed on a wide variety of vegetation. They consume ferns, forbs, and deciduous plants in summer and conifer foliage in fall/winter if other plants are unavailable (Banfield 1974). It forages mainly above the ground (Epple et al. 1993). They require free surface water or succulent vegetation on a daily basis and caches grasses and forbs for winter food. They are active during winter. Throughout the 24-hour day in summer, five to seven periods of activity alternate with periods of rest. They are more active at night than during daylight hours.
Mountain beavers have a low rate of reproduction and are monoestrous. Gestation lasts 28-30 days. One litter of two to four altricial young are born March-April, sometimes as late as early May in the north. Young are weaned in about six to eight weeks. Females are sexually mature in about two years; yearling females may ovulate but do not breed (Carraway and Verts 1993). A few live up to five to six years. They are usually solitary but may live in loose colonies. Population density estimates generally range from four to eight per hectare, but up to 15-20 per ha (Carraway and Verts 1993). The home range of ten adults radio tracked for three to 19 months was 0.03-0.20 ha, with a mean of 0.12 ha (Carraway and Verts 1993). Significant predators of mountain beavers include coyote and bobcat.
Systems
- Terrestrial
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Habitat
The habitat of mountain beavers ranges from forested areas at sea level to timberline peaks. They enjoy areas that contain second growth tree species, shrubs, and prefer to be near water. They are most abundant in high mountain peaks with decidous forest and are least common in coniferous forests. Mountain beavers must live in places with deep soils in order to construct their burrow system. (Carraway, 1993).
Terrestrial Biomes: forest
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Comments: Forested areas from near sea level to timberline. Damp ravines and shaded hillsides in coastal and montane forests with an abundance of herbaceous ground cover. Typically in riparian habitat in moist coniferous forests. Most abundant near water courses in early to mid-seral stages vegetated by a tangle of second growth tree species, shrubs and forbs, and containing debris left from earlier forests (Carraway and Verts 1993). See Beier (1989) for information on habitat in the Sierra Nevada. Prefers damp soils; digs network of tunnels along stream banks. Tunnels generally are just below the ground surface, usually on north slopes in California, on south slopes in British Columbia. Primarily fossorial but can climb trees and swims well (but not arboreal or aquatic). Mostly underground in winter. Oval nests are constructed with leaves, twigs and grasses in a chamber that may be about 2 feet below the surface of the ground.
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Migration
Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.
Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: No. No populations of this species make annual migrations of over 200 km.
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Trophic Strategy
Food Habits
Mountain beavers are herbivorous animals; their diet includes forbs, grasses, and even ferns such as sword fern and bracken fern. The composition of the diet of mountain beavers differs depending on the sex and age of the individual and the season. While they are eating, they squat and emit hard and soft fecal pellets which they catch in their mouths. The hard pellets are put into a pit next to the vegetation while the soft pellets are reingested (Carraway, 1993).
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Comments: Feeds on a wide variety of vegetation; consumes ferns, forbs, and deciduous plants in summer; conifer foliage in fall/winter if other plants are unavailable (Banfield 1974). Forages mainly above ground (Epple et al. 1993). Requires free surface water or succulent vegetation on a daily basis. Caches grasses and forbs for winter food. Coprophagous.
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Population Biology
Number of Occurrences
Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: 81 to >300
Comments: Over a thousand EOs are known from throughout historic range.
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Global Abundance
10,000 to >1,000,000 individuals
Comments: While rare in some relictual populations in California, the species is common over much of the historic range.
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General Ecology
Usually solitary but may live in loose colonies. Population density estimates generally range from 4 to 8 per hectare, but up to 15-20/ha (see Carraway and Verts 1993). Home range of 10 adult radiotracked for 3-19 months was 0.03-0.20 ha (mean 0.12 ha); moved up to 43 m from nest (see Carraway and Verts 1993). Significant predators include coyote and bobcat.
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Life History and Behavior
Cyclicity
Comments: Active during winter. Throughout the 24-hour day in summer, 5-7 periods of activity alternate with periods of rest. More active at night than during daylight hours.
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Life Expectancy
Lifespan/Longevity
Average lifespan
Status: wild: 10.0 years.
Average lifespan
Status: captivity: 6.0 years.
Average lifespan
Status: wild: 6.0 years.
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Lifespan, longevity, and ageing
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Reproduction
Reproduction
Beginning in November or December, there is an increase in the size of the testes, prostate and bulbourethal glands of males. As females reach estrous, their nipples increase in size, their vulva swell, and vaginal smears reveal predominately ephithelial cells. Females that are only a year old ovulate as well but no breeding occurs, demonstrating that ovulation is spontaneous instead of being triggered by copulation. The onset of the estrous cycle is around February or March.
Gestation usually lasts six to eight weeks and litters of two to three young are common. The weight of the young beavers is 25.5g. At birth, the beavers are pink, helpless, blind, and do not have a considerable covering fur. Within six to eight weeks the beavers are able to function (Carraway, 1993).
Average birth mass: 25.5 g.
Average gestation period: 29 days.
Average number of offspring: 2.75.
Average age at sexual or reproductive maturity (male)
Sex: male: 730 days.
Average age at sexual or reproductive maturity (female)
Sex: female: 730 days.
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Low rate of reproduction. Monoestrous. Gestation lasts 28-30 days. One litter of 2-4 (usually 2-3) altricial young born March-April, sometimes as late as early May in north. Young are weaned in about 6-8 weeks. Females sexually mature in about 2 years; yearling females may ovulate but do not breed (see Carraway and Verts 1993). A few live up to 5-6 years.
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Conservation
Conservation Status
IUCN Red List Assessment
Red List Category
Red List Criteria
Version
Year Assessed
Assessor/s
Reviewer/s
Justification
History
- 2000Lower Risk/near threatened
- 1996Lower Risk/least concern
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Conservation Status
The IUCN lists the subspecies A.r. nigra and A.r. phaea of the mountain beaver as indeterminate (Wilson, 1993).
IUCN Red List of Threatened Species: least concern
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National NatureServe Conservation Status
Canada
Rounded National Status Rank: N3 - Vulnerable
United States
Rounded National Status Rank: N5 - Secure
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NatureServe Conservation Status
Rounded Global Status Rank: G5 - Secure
Reasons: Except for two small relictual populations in California, the species is widespread in the Pacific Northwest, common, and not vulnerable to extinction.
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Status
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Trends
Population
Population Trend
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Threats
Threats
Threats to the disjunct subspecies nigra and phaea include wildfire, livestock grazing, expansion of exotic plant species, rodent control measures, alteration of natural stream flow, housing development, highway construction, predation by cats and dogs as well as the general uncertainties associated with small population sizes (Hafner et al. 1998).
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Degree of Threat: D : Unthreatened throughout its range, communities may be threatened in minor portions of the range or degree of variation falls within natural variation
Comments: Common and considered a pest throughout much of range in coastal areas of Northern California, Oregon, Washington and southern British Columbia. Areas inhabitated are generally not visited frequently by humans.
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Management
Conservation Actions
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Management Requirements: Methods used to control depredations by mountain beavers include removing food and cover plants mechanically, with herbicides, or with herbicides and fire; population reduction by use of toxic baits and trapping (number 0 or number 1 steel traps); and use of plastic mesh tubes surrounding tree seedlings (see Carraway and Verts 1993). Predator scents may be useful in controlling browsing damage (Epple et al. 1993).
Biological Research Needs: Many aspects of biology have been studied, but more information on dispersal and demography is needed.
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Global Protection: Few (1-3) occurrences appropriately protected and managed
Comments: California relictual populations are protected in National Park Service land or through state endangered species listing.
Needs: Protect habitat from destruction by logging, burning, water diversion, and excessive livestock grazing.
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Relevance to Humans and Ecosystems
Benefits
Economic Importance for Humans: Negative
Foraging by the mountain beavers on seedlings in areas undergoing reforestation can lead to environmental and economic damage. They also cause garden damage and raid the crops of farmers. To prevent further damage by the mountain beavers, people take various types of action. One is to reduce the food consumed by mountain beavers by using herbicides and burning. Another method is to control the population directly by traps or through using toxic baits. Plastic mesh has also been put around trees that the mountain beavers destroy. These prevention measures add to a considerable amount of money (Carraway, 1993).
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Economic Uses
Comments: May damage young conifers, garden vegetables, and berries. In the 1980s, it was estimated that 121,500 ha of reforestation units were affected (see Engeman et al. 1991). In the Sierra Nevada, damage to conifers is insignificant (see Todd 1992).
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Wikipedia
Mountain Beaver
 | This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (November 2007) |
The Mountain Beaver (Aplodontia rufa) is the most primitive extant rodent. Not to be confused with the North American beaver[2] Castor canadensis, or its relative the Eurasian beaver, Castor fiber[3], it has several common names including Aplodontia, Boomer, Ground Bear, and Giant Mole. The name Sewellel Beaver comes from sewellel or suwellel, the Chinookan term for a cloak made from its pelts. This species is the only living member of its genus, Aplodontia, and family, Aplodontiidae.[4]
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Characteristics
Mountain Beavers are brown in color, but fur can range from slightly more reddish to more blackish depending on subspecies. There is a light patch under each ear. The animals have distinctively short tails. Adults weigh between about 500–900 g (18–32 oz) with a few specimens topping 1,000 g (35 oz). Total length is about 30–50 cm (12–20 in) with a tail length of 1–4 cm (0.39–1.6 in).
The skull is protrogomorphous. This means that it has no specialized attachments for the masseter muscles as seen in other rodents. It is flattened and lacks a postorbital process. The baculum is thin and distinctly forked. The penis is about 4.5 cm (1.8 in) in length. They do not have a true scrotum, but testes move into a position called semiscrotal during the breeding season[citation needed].
Mountain Beavers have an unusual projection on each molar and premolar which is unique among mammals and allows for easy identification of teeth. This projection points toward the cheek on the upper toothrow, but points toward the tongue on the lower. The cheek teeth lack the complex folds of other rodents and instead consist of a single basin. They are hypsodont and ever-growing. Two upper and one lower premolars are present, along with all the molars, giving a dental formula of
| Dentition |
|---|
| 1.0.2.3 |
| 1.0.1.3 |
Mountain Beavers cannot produce concentrated urine. They are thought to be physiologically restricted to the temperate rain forest regions of the North American Pacific coast and moist microenvironments inland due to their inability to obtain sufficient water in more arid environments[citation needed]. Their karyotype is 2n=46.
Habits and distribution
Mountain Beavers are found in the coastal mountains of British Columbia and southward to include the Cascades Mountain ranges, the Siskyous, Sierra Nevada mountain range of Southern California within North America.[5] They range from sea level to the tree line.[5] They can be found in both deciduous and coniferous forests, but throughout most of the range appear to prefer the former. These animals appear to be physiologically limited to moist microenvironments, with most subspecies occurring only in regions with minimal snowfall and cool winters. They do not appear to be able to conserve body heat or warmth as efficiently as other rodents [6]. They do not hibernate.
Mountain Beavers build elaborate burrow systems with chambers devoted to fecal and food caches. They exhibit coprophagy and eat soft fecal pellets to obtain maximum nutrients. Hard fecal pellets are transferred to fecal chambers using their incisors. Food includes fleshy herbs and young shoots of more woody plants. Ferns probably make up the bulk of the diet. They appear to be strictly vegetarian[6]. Their consumption of seedling trees has led some to consider them a pest. They appear to build hay mounds at some burrow entrances, but whether this behavior is related to water regulation, curing food, or gathering nest materials is debated.
A host of other animals have been documented[citation needed] within the burrow system of Mountain Beavers. These include: Long-tailed Weasels, Ermines, Minks, Fishers, American Badgers, raccoons, Western Spotted Skunks, Striped Skunks, Brush Rabbits, Snowshoe Hares, Douglas Squirrels, Western Jumping Mice, Water Voles, California Voles, White-footed Voles, Western Red-backed Voles, Deer Mice, Bushy-tailed Woodrats, Dusky-footed Woodrats, Botta's Pocket Gopher, American Shrew Moles, Coast Moles, and Pacific Giant Salamanders (Carraway and Verts, 1993). Because of their effect on such a wide variety of plants and animals, some ecologists[who?] consider Mountain Beavers to be a keystone species.
Known predators include Bobcats, Coyotes, Cougars, Golden Eagles, and Owls. Among the parasites of the Mountain Beaver is the largest flea known to modern science, Hystrichopsylla schefferi. Females of this flea can be 8 mm (0.31 in) long. [1]
The breeding season is between January-March with 2-3 young born February-April. The young are born hairless, pink, and blind. Longevity is 5–10 years, fairly long as rodents go. They are not social, though home ranges can overlap[6].
Mountain Beavers are capable of climbing trees[7], but rarely travel far from burrows. The thumb is slightly opposable and the animals will sit on their hindquarters and manipulate food with their forelimbs and incisors.
Spelling and etymology
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 to a family name is to drop the -a only and add -idae. Thus, Aplodontiidae is technically correct. This spelling is gaining acceptance in modern texts.
Alternate spellings of the genus name have also been reported, with as many as 30 variants historically. These include Haplodontia, Haplodon, Aploodontia, Apluodontia, and Aplodontie among others. The name Aplodontia means "simple tooth" and is in reference to the single large basin comprising the bulk of each cheek tooth. The specific epithet, rufa means red or reddish.
Subspecies
At present seven subspecies of Aplodontia rufa are recognized.
Aplodontia rufa californica (Peters, 1864)
- Distributed throughout the Sierra Nevada range in Northern California and extreme western Nevada.
Aplodontia rufa humboldtiana Taylor, 1916
- Restricted to the far Northwestern coast of California.
Aplodontia rufa nigra Taylor, 1914
- Restricted to a small region in southern Mendocino County, California.
Aplodontia rufa pacifica Merriam, 1899
- Distributed across coastal Oregon.
Aplodontia rufa phaea Merriam, 1899
- Found in a small pocket just Northwest of San Francisco, California.
Aplodontia rufa rainieri Merriam, 1899
- Found across the Cascade Range from southern British Columbia to northern California.
Aplodontia rufa rufa (Rafinesque, 1817)
- Found along coastal Washington, particularly on the Olympic Peninsula.
Closest relatives
The Mountain Beaver is considered a living fossil by many researchers[who?] due to the presence of a host of primitive characteristics, particularly the protrogomorphous zygomasseteric system. This condition is similar to what is found in most mammal groups, such as rabbits, where no extreme specialization of the masseter muscle has evolved. In the protrogomorphous condition, the masseter muscle does not pass through the infraorbital foramen as it does in guinea pigs and mice. Likewise, the medial masseter muscle attaches to the base of the zygomatic arch and does not extend to the region in front of the eye as is seen in squirrels and mice. The Mountain Beaver is the only living rodent with this primitive cranial and muscular feature (except perhaps the blesmols who clearly evolved protrogomorphy from a hystricomorphous ancestor). The Mountain Beaver was once thought to be related to the earliest protrogomorphous rodents such as the ischyromyids like Paramys. Both molecular and morphological phylogeneticists have recently suggested a more distant relationship to these animals.
Molecular results have consistently produced a sister relationship between the Mountain Beaver and the squirrels (family Sciuridae). This clade is referred to as Sciuroidea, Sciuromorpha (not to be confused with the sciuromorphous zygomasseteric system), or Sciurida depending on the author.
According to the fossil record, the Aplodontioidea split from the squirrels in the Middle or Late Eocene as indicated by the extinct genera †Spurimus and †Prosciurus. The fossil record for the genus Aplodontia itself extends to the Late Pleistocene of North America.
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References
 | Wikimedia Commons has media related to: Aplodontia rufa |
- ^ Fellers, G. M., Lidicker Jr., W. Z., Linzey, A. V. & Nature Serve (Williams, D. F. & Hammerson, G.) (2008). Aplodontia rufa. In: IUCN 2008. IUCN Red List of Threatened Species. Downloaded on 6 January 2009.
- ^ Wood Beaver in The New Encyclopedia of Mammals. David Macdonald (ed). Oxford university Press, 2001. Page 596-597.
- ^ Beavers in The New Encyclopedia of Mammals. David Macdonald (ed). Oxford university Press, 2001. Page 590-591.
- ^ Helgen, Kristofer M. (16 November 2005). "Family Aplodontiidae (p. 753)". In Wilson, Don E., and Reeder, DeeAnn M., eds. Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Baltimore: Johns Hopkins University Press, 2 vols. (2142 pp.). ISBN 978-0-8018-8221-0. OCLC 62265494. http://www.bucknell.edu/msw3/browse.asp?id=12300004.
- ^ a b Mountain Beaver in The New Encyclopedia of Mammals. David Macdonald (ed). Oxford University Press, 2001. Pages 596-597.
- ^ a b c Evans, James (1984). Macdonald, D.. ed. The Encyclopedia of Mammals. New York: Facts on File. pp. 610–611. ISBN 0-87196-871-1.
- ^ Tree Climbing by Mountain Beavers. Lloyd Ingles. Journal of Mammalogy, Vol. 41, No. 1 (Feb., 1960), pages 120-121.
- Adkins, R. M. E. L. Gelke, D. Rowe, and R. L. Honeycutt. 2001. Molecular phylogeny and divergence time estimates for major rodent groups: Evidence from multiple genes. Molecular Biology and Evolution, 18:777-791.
- Carraway, L. N. and B. J. Verts. 1993. Aplodontia rufa. Mammalian Species, 431:1-10.
- McKenna, Malcolm C., and Bell, Susan K. 1997. Classification of Mammals Above the Species Level. Columbia University Press, New York, 631 pp. ISBN 0-231-11013-8
- Nowak, R. M. 1999. Walker's Mammals of the World, Vol. 2. Johns Hopkins University Press, London.
- Feldhammer, George A.; Lee Drickamer, Stephen Vessey, Joseph Merritt, Carey Krajewski (2007). Mammology: Adaptation, Diversity, Ecology. Johns Hopkins University Press.
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Names and Taxonomy
Taxonomy
Comments: This is the only species in this family. Helgen (in Wilson and Reeder 2005) applied the common name "sewellel" to this species. Inasmuch as this name is much less known than the traditional name (mountain beaver) and hinders effective communication, we retain the latter name for now.
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