Aplodontia rufa (Rafinesque, 1817)

Don E. Wilson, Thomas E. Lacher, Jr & Russell A. Mittermeier, 2016, Aplodontiidae, Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I, Barcelona: Lynx Edicions, pp. 642-647 : 647

Mountain Beaver

Aplodontia rufa

French: Aplodonte / German: Stummelschwanzhérnchen / Spanish: Castor de montana

Other common names: Boomer, Sewellel; Point Arena Mountain Beaver (nigra), Point Reyes Mountain Beaver (phaea)

Taxonomy. Anisonyx? rufa Rafinesque, 1817 ,

“neighborhood of the Columbia river,” Pacific Northwest , North America .

The boundaries of the subspecies were recently revised in a study of the population genetics within the species. In 2013 A. J. Piaggio and colleagues determined that the formerly recognized subspecies rainiert was nested within rufa , but that rufa north of the Columbia River represents a distinct population from those to the south, resulting in the resurrection of the subspecies olympica . This study also revised the geographic boundaries for the subspecies pacifica . Seven subspecies recognized.

Subspecies and Distribution.

A.r.rufaRafinesque,1817—NWUSA,fromNOregon(justSofColumbiaRiver)tocoastalSOregonandNCalifornia.

A.r.californicaPeters,1865—SierraNevadaMtsinECaliforniaandextremeWNevada.

A.r.humboldtianaTaylor,1916—HumboldtCounty,coastalNWCalifornia.

A.r.nigraTaylor,1914—PointA.r.,MendocinoCounty,coastalNCalifornia.

A.r.olympicaMerriam,1899—SWCanada(SBritishColumbia)andNWUSA(WWashington),fromtheFraserRiverStotheColumbiaRiver.

A.r.pacificaMerriam,1899—NWcoastofOregonfromthemouthoftheColumbiaRiverStoNewport.

A. r. phaea Merriam, 1899 — Point Reyes, Marin County, coastal N California.

Descriptive notes. Head-body 230-430 mm, tail 20-55 mm, ear 13-30 mm, hindfoot 48-63 mm; weight 0.6-1.4 kg. Female Mountain Beavers are ¢.8-10% smaller than males. Pelage is uniformly dark brown, with long guard hairs and short underfur. The Mountain Beaver has a thick, heavily built body with short limbs, long claws (especially on the manus), and small eyes and ears. Head is broad and flat with wide, robust incisors and ever-growing cheekteeth. There are five digits on manus and pes.

Habitat. Moist temperate forests and forest openings, especially in secondary growth where undergrowth is tangled and thick. Mountain Beavers are found more frequently in deciduous than coniferous forests. The Mountain Beaver generally constructs its burrow close to water sources, often allowing it to flood parts of the tunnel system.

Food and Feeding. The Mountain Beaveris primarily folivorous. Bracken fern (Pteridium aquilinum) and sword fern (Polystichum munitum) are staples of their diet yearround, but they also eat leaves, bark, and twigs of a variety of other plants as available, apparently specializing in plants toxic to other herbivores. When other food sources are scarce in winter, conifer stems and needles are important sources of food, despite their poor food quality. The Mountain Beaver will pull entire plants underground for consumption, but it will also climb a few metersinto trees to collect and eat stems and leaves. In autumn, hay piles are constructed outside burrow entrances that are used for nesting material and food. The Mountain Beaver also requires abundant water because its inability to concentrate urine limits dehydration tolerance.

Breeding. Mountain Beavers breed once a year, in winter, with estrus generally synchronized among females in a population. Young are born in early spring in litters of 2-4 offspring; they are weaned after 6-8 weeks and emerge aboveground soon after weaning. It takes c.2 years to reach adulthood. Life span is estimated at 5-6 years.

Activity patterns. The Mountain Beaver, like many fossorial animals, is cathemeral, being active for several bouts of foraging in a 24hour period;it seems to be most active at night. It does not hibernate, although it is rarely active aboveground in winter.

Movements, Home range and Social organization. Mountain Beavers have small home ranges, with males’ home ranges averaging 0-32 ha and females’ averaging only 0-17 ha. Individuals rarely range far from burrow entrances and spend the majority of their time underground. Even when juveniles disperse from their nests, distance traveled is less than 1 km. The Mountain Beaver is solitary and does not seem to have any social organization.

Status and Conservation. Classified as Least Concern on The IUCN Red List. At the species level, the Mountain Beaver is oflittle conservation concern; populations on the Pacific Northwest coast and in the Sierra Nevada are quite healthy. The “Point Reyes Mountain Beaver” ( phaea ssp.) is considered vulnerable by the State of California, given its small distribution and surrounding human development; this vulnerability was challenged in 1995 when a wildfire in Point Reyes National Seashore burned an area of Mountain Beaver habitat. Mortality of Mountain Beavers in the burned area was ¢.99%, and recovery will take an estimated 15-20 years. The “Point Arena Mountain Beaver” ( nigra ssp.) is listed under the US Endangered Species Act as endangered because habitat loss in the small area it inhabits around Point Arena has led to small population sizes.

Bibliography. Camp (1918), Carraway & Verts (1993), Cox & Faulkes (2014), Dice (1932), Druzinsky (2010), Fellers et al. (2004), Furlong (1906), Hooven (1977), Hopkins (2005, 2008), Hubbard (1922), Ingles (1965), Johnson (1970), Lovejoy & Black (1974), Lovejoy et al. (1978), Martin (1971), Maser et al. (1981), Merzenich et al. (1973), Nolte et al. (1993), Nowak (1999a), O'Brien (1988), Piaggio et al. (2013), Rafinesque (1817), Richardson (1829b), Scheffer, TH. (1929), Scheffer, V.B. (1942), Schmidt-Nielsen & Pfeiffer (1970), Servheen (1978), Seton (1929), Sinclair (1904), Voth (1968), Zielinski et al. (2013).

Figures

Mountain Beaver

Subspecies and Distribution. A.r.rufaRafinesque,1817—NWUSA,fromNOregon(justSofColumbiaRiver)tocoastalSOregonandNCalifornia. A.r.californicaPeters,1865—SierraNevadaMtsinECaliforniaandextremeWNevada. A.r.humboldtianaTaylor,1916—HumboldtCounty,coastalNWCalifornia. A.r.nigraTaylor,1914—PointA.r.,MendocinoCounty,coastalNCalifornia. A.r.olympicaMerriam,1899—SWCanada(SBritishColumbia)andNWUSA(WWashington),fromtheFraserRiverStotheColumbiaRiver. A.r.pacificaMerriam,1899—NWcoastofOregonfromthemouthoftheColumbiaRiverStoNewport. A. r. phaea Merriam, 1899 — Point Reyes, Marin County, coastal N California.