Mountain beaver

{{short description|Species of the genus Aplodontia}} {{more citations needed|date=April 2017}} {{speciesbox | name = Mountain beaver | fossil_range = {{Fossil range|Late Pleistocene|recent}} | image = Aplodontia.jpg | status = LC | status_system = IUCN3.1 | status_ref =<ref name=iucn>{{cite iucn|author1= Fellers, G. M.|author2= Lidicker Jr., W. Z.|author3= Linzey, A.|author4= NatureServe|title= ''Aplodontia rufa'' |errata=2017|year= 2016|article-number= e.T1869A115057269|doi= 10.2305/IUCN.UK.2016-3.RLTS.T1869A22183865.en |access-date= 15 August 2020}}</ref> | taxon = Aplodontia rufa | parent_authority = Richardson, 1829 | authority = (Rafinesque, 1817) | range_map = Aplodontia rufa distribution map.png }}

The '''mountain beaver''' ('''''Aplodontia rufa''''')<ref group="Note">Other names include boomer, mountain boomer, ground bear, giant mole, gehalis, sewellel, suwellel, showhurll, showtl, and showte, as well as a number of other Native American terms. "Mountain beaver" is a misnomer as the animal is not a true beaver (''Castor'') and it is not restricted to mountains. "Boomer" refers to the loud vocalizations that these usually-solitary animals make when in social situations, but this has not been recorded nor verified. Lewis and Clark originally called the animal "sewellel", a misunderstanding of the Chinook word "she-wal-lal", the name for garments made from the skin of the creature. See Borrecco and Anderson, 1980.</ref> is a North American rodent. It is the only living member of its genus, '''''Aplodontia''''', and family, Aplodontiidae.<ref name = MSW3>{{MSW3 Aplodontiidae|id=12300004}}</ref> 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.<ref name="Piaggio">Piaggio, A. J., B. A. Coghlan, A. E. Miscampbell, W. M. Arjo, D. B. Ransome, and C. E. Ritland. 2013. Molecular phylogeny of an ancient rodent family (Aplodontiidae). ''Journal of Mammalogy'' 94(3): 529–543.</ref> There are seven subspecies of mountain beaver, six of which are found in California and three of which are endemic to the state.<ref name="Todd-1990">{{Cite web |last=Todd |first=Paul A. |date=1990 |title=The distribution abundance and habitat requirements of the Sierra mountain beaver in Yosemite National Park |url=https://scholarworks.umt.edu/cgi/viewcontent.cgi?article=8059&context=etd }}</ref>

== Spelling and etymology == thumb|right|Immature mountain beaver 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'' to a family name is to drop the -''a'' only and add ''-{{not a typo|idae}}''. Thus, ''Aplodontiidae'' is technically correct. This spelling is gaining acceptance in modern texts and is the standard spelling currently recognized by the Integrated Taxonomic Information System.

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.

==Taxonomy and phylogeny== [[File:Aplodontia rufa (Harvard University).JPG|thumb|''Aplodontia rufa'' specimen at Harvard University]] Originating in the late Oligocene, the mountain beaver has retained a number of primitive characteristics that make it a living fossil. In particular, it is the only surviving species to retain the Eocene-era protrogomorph chewing mechanism (zygomasseteric system).<ref>{{Cite journal |last=Wood |first=Albert E. |date=1965 |title=Grades and Clades Among Rodents |url=https://www.jstor.org/stable/2406300 |journal=Evolution |volume=19 |issue=1 |pages=115–130 |doi=10.2307/2406300 |jstor=2406300 |issn=0014-3820|url-access=subscription }}</ref>

In the protrogomorphous condition, the medial masseter muscle does not pass through the infraorbital foramen as it does in guinea pigs and mice. Likewise, the lateral 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.<ref>{{cite journal|last1=Hautier|first1=L.|last2=Michaux|first2=J.|last3=Marivaux|first3=L.|last4=Vianey-Liaud|first4=M.|title=Evolution of the zygomasseteric construction in Rodentia, as revealed by a geometric morphometric analysis of the mandible of ''Graphiurus'' (Rodentia, Gliridae)|journal=Zoological Journal of the Linnean Society|volume=154|year=2008|pages=807–821|issue=4|doi=10.1111/j.1096-3642.2008.00453.x|s2cid=84477221}}</ref> Although modern blesmols also share the mountain beaver's primitive, protrogomorphous chewing mechanism, this trait appears to have newly re-evolved in that family.<ref>{{Cite journal |last1=Korth |first1=William W. |last2=Emry |first2=Robert J. |date=November 1991 |title=The skull of Cedromus and a review of the Cedromurinae (Rodentia, Sciuridae) |url=https://www.cambridge.org/core/journals/journal-of-paleontology/article/abs/skull-of-cedromus-and-a-review-of-the-cedromurinae-rodentia-sciuridae/807A7F3975EFDF741F64B6610DDB1EF4 |journal=Journal of Paleontology |language=en |volume=65 |issue=6 |pages=984–994 |doi=10.1017/S0022336000033291 |bibcode=1991JPal...65..984K |issn=0022-3360|url-access=subscription }}</ref>

In addition to its skull and jaw, the mountain beaver's kidneys are notably primitive. Their poor renal function is considered one of the key limits on the species' geographic distribution.<ref name="Piaggio" />

The mountain beaver was once thought to be related to the earliest protrogomorphous rodents, such as the ischyromyids (''Paramys''). Both molecular and morphological phylogeneticists have recently suggested a more distant relationship to these animals.

Molecular studies have revealed the Sciuridae (squirrels) clade as the mountain beaver's closest living relative.<ref name="Piaggio" /> According to the fossil record, the Aplodontiidae clade split from the squirrels in the Middle or Late Eocene as indicated by the extinct genera ''Spurimus'' and ''Prosciurus''.{{citation needed|date=October 2023}}

=== Subspecies === At present, seven subspecies of ''Aplodontia rufa'' are recognized:

*''A. r. californica'' (Peters, 1864): distributed throughout the Sierra Nevada in Northern California and extreme western Nevada *''A. r. humboldtiana'' Taylor, 1916: restricted to the far northwestern coast of California *''A. r. nigra'' Taylor, 1914: restricted to a small region in southern Mendocino County, California *''A. r. pacifica'' Merriam, 1899: distributed across coastal Oregon *''A. r. phaea'' Merriam, 1899: found mostly in Point Reyes, northwest of San Francisco, California *''A. r. rainieri'' Merriam, 1899: found across the Cascade Range from southern British Columbia to southern Washington *''A. r. rufa'' (Rafinesque, 1817): found along coastal Washington, all the way down through Oregon to Northern California

== Description == thumb|Skull of a mountain beaver Mountain beavers are usually dark gray or brown, but their fur can range from slightly more reddish (rufa) to more blackish depending on subspecies, with a light patch under each ear. The animals have distinctively short tails. Adults weigh about {{convert|500|-|900|g|abbr=on}}, with a few specimens topping {{convert|1000|g|abbr=on}}. Total length is about {{convert|30|-|50|cm|abbr=on}}, with a tail length of {{convert|1|-|4|cm|abbr=on}}. Their superficial similarity with true beavers reflects only their relatively large size (for rodents), strong odor, preference for living in extremely watery / moist habitats, and propensity to gnaw bark and cut branches. Mountain beavers do not fell trees, build dams, live in lodges, or communicate by slapping their tails (their tail is minute). They are predominantly nocturnal and crepuscular in above ground activities.<ref>Godwin, A. J. 1964. A review of the literature on the mountain beaver. USDI, Fish and Wildlife Serv., Washington, D.C. Spec. Sci. Rep. Wildl. No. 78. 52 pp.</ref> They are known to climb trees a few meters to acquire food in the form of branches and leaves, but otherwise their diet consists mostly of ferns, especially species that are toxic to other animals.<ref name=carraway>{{cite journal|title=''Aplodontia rufa''|date=23 April 1993|journal=Mamm Species|number=432|pages=1–10|publisher=The American Society of Mammalogists|author1=Leslie N. Carraway|author2=B.J. Verts|url=http://www.science.smith.edu/msi/pdf/i0076-3519-431-01-0001.pdf|access-date=2017-09-09|archive-url=https://web.archive.org/web/20150205002135/http://www.science.smith.edu/msi/pdf/i0076-3519-431-01-0001.pdf|archive-date=2015-02-05}}</ref>

The skull is protrogomorphous; it has no specialized attachments for the masseter muscles as seen in other rodents. It is flattened and lacks a postorbital process.<ref name="Druzinsky">Druzinsky, Robert E. "[http://www.karger.com/Article/PDF/284931 Functional anatomy of incisal biting in Aplodontia rufa and sciuromorph rodents–Part 1: masticatory muscles, skull shape and digging]." Cells Tissues Organs 191.6 (2010): 510–522.</ref> The baculum is thin and distinctly forked.<ref>{{Cite journal |last1=Carraway |first1=Leslie N. |last2=Verts |first2=B. J. |date=1993-04-23 |title=Aplodontia rufa |url=https://academic.oup.com/mspecies/article-lookup/doi/10.2307/3504188 |journal=Mammalian Species |issue=431 |pages=1–10 |doi=10.2307/3504188|jstor=3504188 |url-access=subscription }}</ref> The penis is about {{convert|4.5|cm|abbr=on}} in length. The male does not have a true scrotum, but the testes move into a position called semiscrotal during the breeding season.<ref name="Todd-1990" />

Mountain beavers have an unusual projection on each molar and premolar tooth, which is unique among mammals and allows for easy identification of teeth. This projection points toward the cheek on the upper tooth row, but points toward the tongue on the lower. The cheek teeth lack the complex folds of other rodents and instead consist of single basins. They are hypsodont and ever-growing. Two upper and one lower premolars are present, along with all the molars, giving a dental formula of {{DentalFormula|upper=1.0.2.3|lower=1.0.1.3}}.<ref name="Carraway">citation needed</ref>

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.<ref name="Todd-1990" /> It is thought that ''Aplodontia'' prefer vegetation high in water content due to their poor ability to concentrate urine which makes it necessary to consume large amounts of water daily.<ref name="Borrecco-1980">{{Cite journal|last1=Borrecco|first1=John E.|last2=Anderson|first2=Robert J.|date=1980|title=Mountain beaver problems in the forest of California, Oregon, and Washington|url=https://escholarship.org/uc/item/8mw3n719|journal=Proceedings of the Vertebrate Pest Conference|language=en|volume=9|issue=9|issn=0507-6773}}</ref>

== Habitat and distribution == Mountain beavers are found in the Cascade Mountains of British Columbia and southward including the rest of the Cascade Range in the United States,<ref name="Mammals Macdonald 2001">"Mountain Beaver" in ''The New Encyclopedia of Mammals''. David MacDonald (ed). Oxford University Press, 2001. Pages 596–597.</ref> the Olympic Mountains and Coast Ranges of Washington and Oregon,<ref name=mathews>{{cite book|last=Mathews|first=Daniel|title=Cascade-Olympic Natural History|year=1994|publisher=Audubon Society of Portland/Raven Editions|location=Portland, Oregon|isbn=0-9620782-0-4|url=https://archive.org/details/cascadeolympicna00math}}</ref> plus the Klamath Mountains, and the Sierra Nevada, Point Arena and Pt. Reyes of California and extreme western Nevada. They range from sea level to the tree line.<ref name="Mammals Macdonald 2001"/> They can be found in both deciduous and coniferous forests, but throughout most of the range they appear to prefer the former.

==Behavior== Mountain beavers are capable of climbing trees,<ref>Lloyd Ingles. (1960). Tree Climbing by Mountain Beavers. ''Journal of Mammalogy'', vol. 41, no. 1, (Feb., 1960), pages 120–121.</ref> but rarely travel far from burrows. Their thumbs are slightly opposable and the animals will sit on their hindquarters and manipulate food with their forelimbs and incisors. Mountain beavers are asocial and generally do not live in shared burrows. Burrows usually consist of a network of tunnels built in deep soil. The entrances to these burrows often contain clumps of wilted vegetation which the animal likely uses as a kind of food cache as well as a source of nesting material. Mountain beavers seldom travel more than a few meters from their burrow entrances, taking advantage of the protection such burrows offer from predators, such as cougars and owls (though skunks and weasels that also occupy mountain beaver burrows and tunnels may take nestlings as food).<ref name=carraway/> 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.{{citation needed|date=January 2012}} Mountain beavers are partially nocturnal, spending more time active at night than the day but still active during both periods. They actively feed in periods of up to 2 hours and 45 minutes throughout the day with 6 or 7 periods of feeding per day. In total they forage for up to 9 hours per day.<ref name="Todd-1990" /> These animals are 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,<ref name=EoM>{{cite book|editor= MacDonald, D.|author= Evans, James|year= 1984|title= The Encyclopedia of Mammals|publisher= Facts on File|location= New York|pages= [https://archive.org/details/encyclopediaofma00mals_0/page/610 610–611]|isbn= 0-87196-871-1|url=https://archive.org/details/encyclopediaofma00mals_0/page/610}}</ref> nor do they hibernate.

==Diet== thumb|left|Mountain beaver burrow They exhibit coprophagy and eat soft fecal pellets to obtain maximum nutrients; hard fecal pellets are transferred to fecal chambers located within the burrow system.<ref>{{cite web|url=http://animaldiversity.ummz.umich.edu/accounts/Aplodontia_rufa/|author=Newell, Toni Lynn |year=2002|title=''Aplodontia rufa'' mountain beaver |publisher=Animal Diversity Web|access-date=2013-08-11}}</ref><ref>{{cite web|url=http://icwdm.org/handbook/rodents/MountainBeaver.asp|author=Campbell, Dan L.|year=2005|title=Mountain Beavers and Control of Mountain Beaver Damage|publisher=Internet Center for Wildlife Damage Management|access-date=2013-08-12|archive-url=https://web.archive.org/web/20181202200300/http://icwdm.org/handbook/rodents/MountainBeaver.asp|archive-date=2018-12-02}}</ref> Food includes fleshy herbs and young shoots of more woody plants. Ferns probably make up the bulk of their diets. They appear to be strictly herbivorous.<ref name=EoM/> Their consumption of seedling trees has led some to consider them as pests.

==Ecology== Known predators include bobcats, coyotes, weasels, cougars, golden eagles, and owls.<ref>{{Cite web |url=http://icwdm.org/handbook/rodents/MountainBeaver.asp |title=Oregon Dept of Forestry info page |access-date=2013-03-30 |archive-url=https://web.archive.org/web/20181202200300/http://icwdm.org/handbook/rodents/MountainBeaver.asp |archive-date=2018-12-02 }}</ref>

Among the parasites of the mountain beaver is the largest flea known, ''Hystrichopsylla schefferi''. Females of this flea can be {{convert|8|mm|abbr=on}} long.<ref>{{cite web|url=http://wdfw.wa.gov/living/mtn_beavers.html|title=Living with Wildlife: Mountain Beavers|publisher=Washington Department of Fish and Wildlife|access-date=2013-06-25}}</ref>

Mountain beavers are considered pests in areas of the Pacific Northwest because of the extensive damage they cause to forest trees due to basal-grinding (removal of bark), branch cutting, or clipping small saplings and seedlings. This damage often poses a problem for forest management and reforestation when smaller seedlings are buried or uprooted during mountain beaver feeding and can result in tree deformities, growth suppression, and mortality.<ref name="Borrecco-1980" /> The United States Forest Service has maintained a program to exterminate the mountain beaver due to beavers causing economic damage to commercial reforestation.<ref>{{cite book|last=Hygnstrom|first=Scott|title=Prevention and Control of Wildlife Damage|year=2010|publisher=Diane Pub Co|isbn=978-1-4379-3688-9|pages=B-59|url=https://books.google.com/books?id=gt-Yk3CRuXMC}}</ref> Damage control measures taken to protect forest trees by controlling the mountain beaver population include trapping, placing toxic baits, and placing physical barriers (e.g., plastic mesh tubes) around the base of an individual tree.<ref>{{Cite news|last=Taylor|first=Jimmy|date=2013|title=Identifying and Managing Mountain Beaver Damage to Forest Resources|work=Oregon State University {{!}} Extension Service|url=https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/em9063.pdf}}</ref>

==Breeding== The breeding season is between January and March, with two or three young born February to April. The ovulation period lasts a few weeks and gestation lasts for a month. The young are born hairless, pink, and blind. They are weaned at 6 to 8 weeks and leave the burrow soon after.<ref name="Todd-1990" /> Lifespans are 5 to 10 years – fairly long for rodents. They are not social, though home ranges can overlap.<ref name=EoM/> While mountain beavers are generally solitary creatures, they may form groups due to suitable habitat and food resources being in a small area; population densities vary widely because of this.<ref>{{cite book|last=Feldhamer|first=George|author2=Bruce Thompson|author3=Joseph Chapman|title=Wild Mammals of North America: biology, management, and conservation|year=2003|publisher=Johns Hopkins University Press|isbn=978-0-8018-7416-1|pages=179–187|url=https://books.google.com/books?id=-xQalfqP7BcC}}</ref>

==Status and conservation==

The IUCN lists the mountain beaver as a species of least concern. However, one subspecies, the Point Arena mountain beaver (''A. r. nigra'') of California, is considered endangered by the U.S. Fish and Wildlife Service,<ref name=fws>{{cite web|url=https://www.fws.gov/arcata/es/mammals/mtnbeaver/mtnbeaver.html|title= Point Arena Mountain Beaver Species Profile|access-date=2021-09-06}}</ref> and ''Critically Imperiled'' by NatureServe.<ref>{{cite web |title=NatureServe Explorer 2.0 |url=https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.104721/Aplodontia_rufa_nigra |website=explorer.natureserve.org |access-date=15 November 2022}}</ref> Originally listed in 1991, the Point Arena mountain beaver is distinguished by its black colouration and by characteristic body proportions, including a smaller overall size.<ref>{{cite web|url=https://www.fws.gov/arcata/es/mammals/mtnbeaver/documents/5yearReview.pdf|title=Point Arena Mountain Beaver (''Aplodontia rufa nigra'') 5-Year Review: Summary and Evaluation}}</ref> The principal threat to this subspecies is habitat loss and fragmentation; its remaining range comprises a disjunct region of {{convert|24|mi2}} in western Mendocino County.<ref name=fws/>

==Notes== {{Reflist|group=Note}}

==References== {{Reflist}} * 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. * 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. * {{cite book|last=Feldhammer|first=George A.|author2=Lee Drickamer|author3=Stephen Vessey|author4=Joseph Merritt|author5=Carey Krajewski|title=Mammalogy: Adaptation, Diversity, Ecology|publisher=Johns Hopkins University Press|year=2007|isbn=978-0-8018-8695-9|url-access=registration|url=https://archive.org/details/mammalogyadaptat03edunse}}

== External links == * {{Commons category-inline|Aplodontia rufa}}

Category:Mammals described in 1817 Category:Fauna of the Sierra Nevada (United States) Category:Rodents of Canada Category:Rodents of the United States Category:Extant Pleistocene first appearances Category:Taxa named by Constantine Samuel Rafinesque Category:Endemic fauna of the Pacific Northwest Category:Aplodontiidae