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Article: North American beaver
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{{Use mdy dates|date=March 2013}}
| name = ''Castor canadensis''
| status = LC
| status_system = iucn3.1
| status_ref = <ref name=iucn>{{IUCN2011.2|assessors=Linzey, A. V. & NatureServe (Hammerson, G. & Cannings, S.)|year=2011|id=4003|title=Castor canadensis|downloaded=January 18, 2012}}</ref>
| image = American Beaver.jpg
| image_caption = A male North American beaver
| regnum = [[Animal]]ia
| phylum = [[Chordata]]
| classis = [[Mammal]]ia
| ordo = [[Rodent]]ia
| familia = [[Castoridae]]
| genus = ''[[Beaver|Castor]]''
| species = '''''C. canadensis'''''
| binomial = ''Castor canadensis''
| binomial_authority = [[Heinrich Kuhl|Kuhl]], 1820
| subdivision_ranks = [[Subspecies]]<ref name = MSW3/><ref name="warner">Warner, Richard E. and Hendrix, Kathleen M. (eds.). [ California Riparian Systems: Ecology, Conservation, and Productive Management] University of California Press, 1984, p. 952. Retrieved on August 4, 2007.</ref><ref>[ Browse Genus equals Castor by Scientific Name for All Museums]. Berkeley Natural History Museums. Retrieved on August 4, 2007.</ref><ref>Tesky, Julie L. [ Wildlife Species: Castor canadensis] Fire Effects Information System (Online), U.S. Department of Agriculture, Forest Service,
[[Rocky Mountain Research Station]], Fire Sciences Laboratory. 1993. Retrieved on August 4, 2007.</ref>
| subdivision =
* ''C. c. acadicus'' Bailey
* ''C. c. baileyi'' Nelson
* ''C. c. belugae'' Taylor<br/><small>Cook Inlet beaver</small>
* ''C. c. caecator'' Bangs<br/><small>Newfoundland beaver</small>
* ''C. c. canadensis'' Kuhl<br/><small>Canadian beaver</small>
* ''C. c. concisor''
* ''C. c. carolinensis'' Rhoads<br/><small>Carolina beaver</small>
* ''C. c. duchesnei''
* ''C. c. frondator'' Mearns<br/><small>Sonora beaver</small>
* ''C. c. idoneus''
* ''C. c. labradorensis''
* ''C. c. leucodonta'' Gray<br/><small>Pacific beaver</small>
* ''C. c. mexicanus'' Bailey<br/><small>Rio Grande beaver</small>
* ''C. c. michiganensis'' Bailey<br/><small>Woods beaver</small>
* ''C. c. missouriensis'' Bailey<br/><small>Missouri River beaver</small>
* ''C. c. pacificus'' Rhoads<br/><small>Washington beaver</small>
* ''C. c. pallidus''
* ''C. c. phaeus'' Heller<br/><small>Admiralty beaver</small>
* ''C. c. rostralis''
* ''C. c. repentinus'' Goldman
* ''C. c. sagittatus''
* ''C. c. shastensis'' Taylor<br/><small>Shasta beaver</small>
* ''C. c. subauratus'' <br/><small>California Golden beaver</small>
* ''C. c. taylori'' Davis
* ''C. c. texensis'' Bailey<br/><small>Texas beaver</small>
| range_map = American beaver map.png
| range_map_caption = Distribution of the North American beaver (dark green&nbsp;– native, light green&nbsp;– introduced)
The '''North American beaver''' (''Castor canadensis'') is one of two [[Extant taxon|extant]] [[beaver]] [[species]]. It is native to [[North America]] and introduced to [[Patagonia]] in [[South America]] and some European countries (e.g., [[Norway]]). In the [[United States]] and [[Canada]], the species is often referred to simply as "beaver", though this causes some confusion because another distantly related rodent, ''[[Aplodontia rufa]]'', is often called the "[[mountain beaver]]". Other vernacular names, including '''American beaver'''<ref name = MSW3>{{MSW3 Castoridae | id = 12600004 | page = 842}}</ref> and '''Canadian beaver''',<ref>{{cite web|author=Invasive Species Specialist Group (ISSG)|year=2006|title=''Castor canadensis'' (mammal)|publisher=IUCN Species Survival Commission|work=Global Invasive Species Database (GISD)|url=|accessdate=July 16, 2009|postscript=: "Common names: American beaver (English), beaver (English), Canadian beaver, castor (French), castor americano (Spanish), North American beaver (English)"}}</ref> distinguish this species from the other [[Extant taxon|extant]] beaver species, ''[[Castor fiber]]'', which is native to [[Eurasia]].
This beaver is the largest rodent in [[North America]] and the second or third largest rodent in the world, after the [[South America]]n [[capybara]]. The species' Eurasian counterpart, the [[European beaver]] reaches similarly large sizes. Adults usually weigh from {{convert|11|to|32|kg|lbs|abbr=on}}, with {{convert|20|kg|lbs|abbr=on}} being a typical mass. The head-and-body length is {{convert|74|-|90|cm|in|abbr=on}}, with the tail adding a further {{convert|20|-|35|cm|in|abbr=on}}. Very old individuals can exceptionally exceed normal sizes, weighing more than {{convert|40|kg|lb|abbr=on}} or even as much as {{convert|50|kg|lbs|abbr=on}}.<ref>{{cite web|url= |title=Home Page, Alaska Department of Fish and Game | |accessdate=March 16, 2013}}</ref><ref>[ The Beaver&nbsp;– Life Tracks].</ref><ref name="Burnie">Burnie D and Wilson DE (Eds.), ''Animal: The Definitive Visual Guide to the World's Wildlife''. DK Adult (2005), ISBN 0789477645</ref><ref>Boyle, Steve and Owens, Stephanie (February 6, 2007) [ North American Beaver (''Castor canadensis''): A Technical Conservation Assessment]. USDA Forest Service, Rocky Mountain Region</ref>
Like the capybara, the beaver is [[semi-aquatic]]. The beaver has many traits suited to this lifestyle. It has a large flat paddle-shaped tail and large, webbed hind feet reminiscent of a human diver's [[swimfin]]s. The unwebbed front paws are smaller, with claws. The eyes are covered by a [[nictitating membrane]] which allows the beaver to see underwater. The nostrils and ears are sealed while submerged. A thick [[Subcutaneous fat|layer of fat under its skin]] insulates the beaver from its cold water environment.
The beaver's [[fur]] consists of long, coarse outer hairs and short, fine inner hairs (see [[Double coat]]). The fur has a range of colours but usually is dark brown. [[Scent gland]]s near the genitals secrete an oily substance known as [[castoreum]], which the beaver uses to waterproof its fur.
Before their near [[Local extinction|extirpation]] by trapping in North America, beaver were practically ubiquitous and lived from the [[tundra|arctic tundra]] to the deserts of northern [[Mexico]], and from the [[Atlantic Ocean|Atlantic]] to the [[Pacific Ocean]]s.<ref>{{cite book |title=The American Beaver and his Works |author=Morgan, Lewis H. |year=1868 |publisher=J. B. Lippincott & Co. |page=32 |url=}}</ref><ref name=Naiman>{{cite journal |title=Alteration of North American Streams by Beaver |author=Naiman, Robert J.; Johnston, Carol A. and Kelley, James C. |journal=BioScience |date=Dec 1988 |pages=753–762 |url= |accessdate=Feb 28, 2010 }}</ref> Physician naturalist [[Edgar Alexander Mearns]]' 1907 report of beaver on the [[Sonora River]] may be the southernmost extent of the range of this North American aquatic mammal.<ref>{{cite book |title=Mammals of the Mexican boundary of the United States: A descriptive catalogue of the species of mammals occurring in that region; with a general summary of the natural history, and a list of trees |author=Mearns, Edgar Alexander |page=359 |publisher=Government Printing Office |year=1907 |url=}}</ref> However, beaver have also been reported both historically and contemporaneously in Mexico on the [[Colorado River]], [[Bavispe River]] and [[San Bernardino River]].<ref>{{cite journal |title=Status of Beavers (Castor Canadensis Frontador) in Rio Bavispe, Sonora, Mexico |journal=The Southwestern Naturalist |date=Sep 2002 |url= |accessdate=November 25, 2011 |author=Gallo-Reynoso, Juan-Pablo; Suarez-Gracida, Gabriela; Cabrera-Santiago, Horacia; Coria-Galindo, Else; Egido-Villarreal, Janitzio and Ortiz, Leo C. }}</ref>
[[File:2011.12.17 Beaver skull from SF Bay shore, CA 028 c.jpg|thumb|Skull of a North American Beaver found on San Francisco Bay shore]]
[[File:Biberburg.jpg|thumb|left|Beaver lodge, [[Ontario]], Canada]]
[[File:BeaverDam 8409.jpg|thumb|left|Beaver dam, northern [[California]], USA]]
Beavers are mainly active at night. They are excellent swimmers and may remain submerged for up to 15 minutes. More vulnerable on land, they tend to remain in the water as much as possible. They use their flat, scaly tail both to signal danger by slapping the surface of the water and as a location for fat storage.
They construct their homes, or "lodges," out of sticks, twigs, rocks and mud in [[lake]]s, [[stream]]s, and [[tide|tidal]] [[river delta]]s.<ref name=skagit>{{cite news |title=Scientist discovers beavers building prime salmon habitat in Skagit Delta |author=Mapes, Lynda V. |publisher=The Seattle Times |date=May 18, 2009 |url= |accessdate=June 22, 2010 }}</ref> These lodges may be surrounded by water, or touching land, including burrows dug into river banks. They are well known for building [[dam]]s across streams and constructing their lodge in the artificial pond which forms. When building in a pond, the beavers first make a pile of sticks and then eat out one or more underwater entrances and two platforms above the water surface inside the pile. The first is used for drying off. Towards winter, the lodge is often plastered with mud which when it freezes has the consistency of concrete. A small air hole is left in the top of the lodge.
The [[Beaver dam|dam]] is constructed using logs from trees the beavers cut down, as well as rocks, grass and mud. The inner bark, twigs, shoots and leaves of such trees are also an important part of the beaver's diet.<ref>{{cite journal |title=An extensive study of the foraging ecology of beavers (''Castor canadensis'') in relation to habitat quality |author=Gallant, D., Bérubé, C.H.; Tremblay, E. and Vasseur, L. |year=2004 |journal=Canadian Journal of Zoology |url= |volume=82|pages=922–933 |accessdate=May 4, 2010 |doi=10.1139/z04-067 |issue=6 }}</ref> The trees are cut down using their strong [[incisor]] teeth. Their front paws are used for digging and carrying and placing materials. Some researchers have shown that the sound of running water dictates when and where a beaver builds its dam. Besides providing a safe home for the beaver, beaver ponds also provide habitat for [[waterfowl]], [[fish]], and other aquatic animals. Their dams help reduce soil [[erosion]] and can help reduce flooding. However, beaver dams are not permanent and depend on the beavers' continued presence for their maintenance. Beavers generally concentrate on building and repairing dams in the fall in preparation for the coming winter. In northern areas they often don't repair breaches in the dam made by otters, and sometimes breach the dam themselves and lower the water level in the pond in order to create more breathing space under the ice or get easier access to trees below the dam. In a 1988 study in Alberta, Canada, no beavers repaired "sites of water loss" during the winter. Of 178 sites of water loss, beavers repaired 78 when water was opened, and did not repair 68. The rest were partially repaired.<ref>Donald G. Reid, Stephen M. Herrero and Thomas E. Code, "River Otters as Agents of Water Loss from Beaver Ponds," Journal of Mammalogy, February 1988.</ref>
Beavers are most famous, and infamous, for their dam-building. They maintain their pond-habitat by reacting quickly to the sound of running water, and damming it up with tree branches and mud. Early ecologists believed that this dam-building was an amazing feat of architectural planning, indicative of the beaver's high intellect. This theory was questioned when a recording of running water was played in a field near a beaver pond. Despite the fact that it was on dry land, the beaver covered the tape player with branches and mud.<ref name = Richard>{{cite journal | author = Richard P.B. | year = 1983 | title = Mechanisms and adaptation in the constructive behaviour of the beaver (C. fiber L.) | journal = Acta Zoologica Fennica | volume = 174 | pages = 105–108 }}</ref> The largest beaver dam is {{convert|2790|ft|abbr=on}} in length—more than half a mile long—and was discovered via satellite imagery in 2007.<ref>{{cite web|author=Thie, Jean |url= |title=National Geographic photos | |accessdate=March 16, 2013}}</ref> It is located on the southern edge of [[Wood Buffalo National Park]] in northern [[Alberta]] and is twice the width of the [[Hoover Dam]] which spans {{convert|1244|ft|abbr=on}}.<ref>{{cite news |title=Beaver Dam Seen from Space |author=Soodin, Vince |newspaper=The Sun |url= |accessdate=May 5, 2010 }}</ref>
[[File:Beaver in Winter, Gatineau Park.jpg|thumb|left|''C. c. canadensis'', feeding in winter]]
Normally, the purpose of the dam is to provide water around their lodges that is deep enough that it does not freeze solid in winter. The dams also flood areas of surrounding forest, giving the beaver safe access to an important food supply, which is the leaves, buds, and inner bark of growing trees. They prefer aspen and poplar, but will also take birch, maple, willow, alder, black cherry, red oak, beech, ash, hornbeam and occasionally pine and spruce.<ref>{{cite book |title=The Beaver: Natural History of a Wetlands Engineer |pages=67–75 |url=|publisher=Cornell University Press |year=2003 |isbn=978-0-8014-4098-4 |author=Müller-Schwarze, Dietland and Sun, Lixing }}</ref> They will also eat [[cattails]], [[Nymphaeaceae|water lilies]] and other aquatic vegetation, especially in the early spring (and contrary to widespread belief,<ref>Young, Mary Taylor (August 13, 2007). [ Colorado Division of Wildlife: Do Beavers Eat Fish?]</ref> they do not eat fish). In areas where their pond freezes over, beavers collect food in late fall in the form of tree branches, storing them underwater (usually by sticking the sharp chewed base of the branches into the mud on the pond bottom), where they can be accessed through the winter. Often the pile of food branches projects above the pond and collects snow. This insulates the water below it and keeps the pond open at that location.
Beavers usually mate for life. The young beaver "kits" typically remain with their parents for up to two years.
[[File:Brooklyn Museum - American Beaver - John J. Audubon.jpg|thumb|left|Brooklyn Museum - American Beaver - John J. Audubon]]
Common natural predators include [[Gray Wolf|gray wolves]], [[coyote]]s, and [[Cougar|mountain lions]]. Beaver can be particularly important food for lone wolves.<ref>Thurber, J. M., & Peterson, R. O. (1993). ''Effects of population density and pack size on the foraging ecology of gray wolves''. Journal of Mammalogy, 879-889.</ref> [[American black bear]]s may also prey on beavers if the opportunity arises, often by smashing their paws into the beaver's lodges.<ref name="Frequently Asked Questions About Black Bears">{{cite web|title=The American Bear Association Home Page (Web Pages2/index)|url=|publisher=The American Bear Association}}</ref><ref name="Adirondack Black Bears">{{cite web|title=Adirondack Black Bears|url=|publisher=Environmental Information Series}}</ref><ref>Smith, D. W., Trauba, D. R., Anderson, R. K., & Peterson, R. O. (1994). ''Black bear predation on beavers on an island in Lake Superior''. American Midland Naturalist, 248-255.</ref> Perhaps due to differing habitat preferences, [[Brown bear]]s were not known to hunt beavers in [[Denali National Park]].<ref>Engelhart, A., & Müller-Schwarze, D. (1995). ''Responses of beaver (Castor canadensis Kuhl) to predator chemicals''. Journal of Chemical Ecology, 21(9), 1349-1364.</ref> Less significant predators include [[wolverine]]s, [[Canadian lynx]], [[bobcat]]s, and [[fox]], which are increasingly unlikely to take full-grown beavers due to their smaller size, and [[American alligator]]s, which only minimally co-exist with beavers. Both [[Golden Eagle]]s (''Aquila chrysaetos'') and [[Bald Eagle]]s (''Haliaeetus leucocephalus'') may on occasion predate a beaver, most likely only small kits.<ref name= "Beaver">{{cite web |url= |title=Beaver |publisher=Study of Northern Virginia Ecology, Fairfax County Public School |accessdate=2013-01-03}}</ref> Despite repeated claims there is no evidence that [[Northern river otter|river otters]] are predators of beavers.<ref>{{cite book |title=The Beaver: Natural History of a Wetlands Engineer |pages=113–114 |url=|publisher=Cornell University Press |year=2003 |isbn=978-0-8014-4098-4 |author=Müller-Schwarze, Dietland and Sun, Lixing }}</ref>
North American beaver have one litter per year, coming into estrus for only 12 to 24 hours, between late December and May but peaking in January. Unlike most other rodents, beaver pairs are monogamous, staying together for multiple breeding seasons. Gestation averages 128 days and they average two to three kits per litter with a range of two to six kits.<ref name="Beaver Biology">{{cite web|title=Beaver Biology|url=|publisher=Beaver Solutions|accessdate=22 November 2013}}</ref> Most beaver do not reproduce until they are three years of age, but about 20% of two-year-old females reproduce.<ref>{{cite book |title=The Beaver: Natural History of a Wetlands Engineer |page=80 |url=|publisher=Cornell University Press |year=2003 |isbn=978-0-8014-4098-4 |author=Müller-Schwarze, Dietland and Sun, Lixing}}</ref>
The first fossil records of beaver are 10 to 12 million years old in Germany, and they are thought to have migrated to North America across the [[Bering Strait]]. The oldest fossil record of beaver in North America are of two beaver teeth near [[Dayville, Oregon]] and are 7 million years old.<ref>{{cite web |title=N. America's Earliest Beaver Found Near Dayville&nbsp;– Discovered Teeth "A Dam Important Find,' Scientists Say |publisher=KVTZ |date=September 19, 2011 |url= |accessdate=September 20, 2011 }}</ref>
At one time, 25 subspecies of beaver were identified in North America, with distinctions based primarily on slight morphological differences and geographical isolation at the time of discovery. However, modern techniques generally use genetics rather than morphology to distinguish between subspecies, and currently the Integrated Taxonomic Information System, (which provides authoritative taxonomic information on plants, animals, fungi, and microbes of North America and the world), does not recognize any subspecies of ''C. canadensis, ''though a'' ''definitive genetic analysis has not been performed. Such an analysis would be complicated by the fact that there has been substantial genetic mixing of populations because of the numerous reintroduction efforts intended to help the species recover following extirpation from many regions.
The most widespread (formerly recognized) subspecies, which perhaps are now best thought of as populations with some distinct physical characteristics, are ''C. c. acadicus'' (New England beaver), ''C. c. canadensis'' (Canadian beaver), ''C. c. carolinensis'' (Carolina beaver), and ''C. c. missouriensis'' (Missouri River beaver).<ref name="baker">Baker, B. W., and E. P. Hill. [ Beaver (Castor canadensis)]. G. A. Feldhamer, B. C. Thompson, and J. A. Chapman, editors. Wild Mammals of North America: Biology, Management, and Conservation. Second Edition. The Johns Hopkins University Press, Baltimore, Maryland, USA, pp. 288–310. 2003. Retrieved on August 4, 2007.</ref> The Canadian beaver originally inhabited almost all of the forested area of Canada,<ref>Kieffer, Michael [ Meadows in Mist] Bull Run Mountains Conservancy, Inc. Retrieved on August 4, 2007.</ref> and because of its more valued fur, was often selected for reintroductions elsewhere. The Carolina beaver is found in the southeastern United States, the Missouri River beaver, as its name suggests, is found in the [[Missouri River]] and its tributaries, and ''C. c. acadicus'' is found throughout the [[New England]] area in the northeastern United States.
==Differences from European beaver==
Although superficially similar to the [[European beaver]] (''Castor fiber''), there are several important differences between the two species. North American beavers tend to be slightly smaller, with smaller, more rounded heads, shorter, wider muzzles, thicker, longer and darker underfur, wider, more oval-shaped tails and have longer shin bones, allowing them a greater range of bipedal locomotion than the European species. North American beavers have shorter nasal bones than their European cousins, with the widest point being at the middle of the snout for the former, and in the tip for the latter. The nasal opening for the North American species is square, unlike that of the European race which is triangular. The ''[[foramen magnum]]'' is triangular in the North American beaver, and rounded in the European. The [[anal gland]]s of the North American beaver are smaller and thick-walled with a small internal volume compared to that of the European species. Finally, the guard hairs of the North American beaver have a shorter hollow medulla at their tips. Fur colour is also different. Overall, 50% of North American beavers have pale brown fur, 25% are reddish brown, one fifth are brown and 6% are blackish, while in European beavers 66% have pale brown or beige fur, 20% have reddish brown, nearly 8% are brown and only 4% have blackish coats.<ref name="andy">{{cite book | author= Kitchener, Andrew | title=Beavers | year=2001 | isbn= 1-873580-55-X | page= 144 }}</ref>
The two species are not genetically compatible. North American beavers have 40 [[chromosomes]], while European beavers have 48. Also, more than 27 attempts were made in Russia to hybridize the two species, with one breeding between a male North American beaver and a female European resulting in one stillborn kit. These factors make interspecific breeding unlikely in areas where the two species' ranges overlap.<ref name="andy" />
The beaver was trapped out and almost extirpated in North America as its fur and [[castoreum]] were highly sought after.<ref name=Naiman /> The beaver furs were used to make clothing and [[beaver hat]]s. In the United States extensive trapping began in the early 17th century with more than 10,000 beaver per year taken for the fur trade in [[Connecticut]] and [[Massachusetts]] between 1620 and 1630.<ref>{{cite book |title=The Fur Trade in New England, 1620–1676 |author=Moloney, F. X. |year=1967 |publisher=Archon Books |location=Hamden, Connecticut |page=150 }}</ref> From 1630 to 1640, approximately 80,000 beaver were taken annually from the [[Hudson River]] and western New York.<ref>{{cite journal |title=Notes on the range of some of the animals in America at the time of arrival of the whitemen |author=Hays, W. J. |date=Sep 1871 |journal=The American Naturalist |volume=5 |issue=7 |pages=25–30 |jstor=2447602 }}</ref> As eastern beaver populations were depleted, French and American trappers pushed west. In fact, much of the westward expansion and exploration of North America was driven by the quest for this animal's fur. Before the 1849 [[California Gold Rush]], there was an earlier 19th century [[California Fur Rush]] which drove the earliest American settlement in that State. During the approximately 30 years (1806–1838) of the era of the [[Mountain Man]], the West from Missouri to California and from Canada to Mexico was thoroughly explored and the beaver was brought to the brink of extinction.
With protection in the late 19th and early 20th centuries the current beaver population has rebounded to an estimated 10 to 15 million; however this is still a fraction of the originally estimated 100 to 200 million North American beaver before the days of the [[fur trade]].<ref>Seton-Thompson, cited in {{cite book |last =Sun |first =Lixing |coauthors =Müller-Schwarze, Dietland |title =The Beaver: Natural History of a Wetlands Engineer |publisher =Cornell University Press |year =2003 |location=Ithaca, NY |pages=97–98 |url =|isbn = 0-8014-4098-X}}; but note that to arrive at this figure he assumed a population density throughout the range equivalent to that in [[Algonquin Park]]</ref><ref>{{cite book |title=Water:A Natural History |author=Outwater, Alice |publisher=Basic Books |year=1997 |location=New York, NY |page=89 |isbn=0-465-03780-1 |url=}}</ref>
These animals are considered [[pest (animal)|pest]]s in some parts of their range because their dams can cause flooding in nearby areas, or because their habit of cutting down trees can pose danger to people, as for instance, in [[Charlotte, North Carolina]]'s [[Park Road Park (Charlotte, North Carolina)|Park Road Park]].<ref>{{cite web|url= |title=South Charlotte Weekly: Beavers damaging Park Road Park; must go |author=Parks, Mike |date=March 1, 2012 |}}</ref> Because they are persistent in repairing any damage to the dam, they were historically relocated or exterminated. However, non-lethal methods of containing beaver-related flooding have been developed.<ref>{{cite web|url= |title=Beavers: Wetlands & Wildlife: Solutions to Beaver/Human Conflicts | |accessdate=March 16, 2013}}</ref> One such [[flow device]] has been utilized by both the Canadian and U.S. governments, called "Beaver Deceivers," or levelers, invented and pioneered by wildlife biologist, Skip Lisle.<ref>{{cite news |title=Beaver Deceiver expert coming to Pitkin County |author=Agar, Charles |newspaper=The Aspen Times |location=Aspen, Colorado |date=March 24, 2008 |url= |accessdate=Nov 22, 2009 }}</ref>
The beaver is a [[keystone species]], increasing biodiversity in its territory through creation of beaver ponds and wetlands.<ref>{{cite journal |author=Wright, J.P. |coauthors=Jones, C.G.; Flecker, A.S. |year=2002 |title=An ecosystem engineer, the beaver, increases species richness at the landscape scale |journal=Oecologia |volume=132 |issue=1 |pages=96–101 |url= |accessdate = March 1, 2010 |doi=10.1007/s00442-002-0929-1 }}</ref> As wetlands are formed and riparian habitats enlarged, aquatic plants colonize newly available watery habitat. Insect, invertebrate, fish, mammal, and bird diversity are also expanded.<ref name=Rosell>{{cite journal |title=Ecological impact of beavers Castor fiber and Castor canadensis and their ability to modify ecosystems |author=Rosell F, Bozser O, Collen P, Parker H |journal=Mammal Review |year=2005 |pages=248–276 |url= |accessdate=March 1, 2010 |doi=10.1111/j.1365-2907.2005.00067.x |volume=35 |issue=3–4 }}</ref>
===Effects on stream flows and water quality===
Beaver ponds increase stream flows in seasonally dry streams by storing run-off in the rainy season, which raises groundwater tables via percolation from beaver ponds. In a recent study using 12 serial aerial photo mosaics from 1948 to 2002, the impact of the return of beaver on open water area in east-central [[Alberta]], Canada found that the mammals were associated with a 9-fold increase in open water area. Beaver returned to the area in 1954 after a long absence since their extirpation by the fur trade in the nineteenth century. Even during drought years, where beaver were present, there was 60% more open water than those same areas during previous drought periods when beaver were absent. The authors concluded that beaver have a dramatic influence on the creation and maintenance of wetlands even during extreme drought.<ref>{{cite journal |title=Beaver (''Castor canadensis'') mitigate the effects of climate on the area of open water in boreal wetlands in western Canada |journal=Biological Conservation |year=2008 |url=|pages=556–567|doi=10.1016/j.biocon.2007.12.003|author=Hood, Glynnis A. and Bayley, Suzanne E.}}</ref><ref>{{cite journal |title=Busy Beavers Can Help Ease Drought |journal=Science Daily |date=February 26, 2008 |url= |accessdate=February 23, 2011 }}</ref>
From streams from the [[Maryland]] coastal plain in the east to [[Lake Tahoe]] in the west, beaver ponds have been shown to remove sediment and pollutants including total suspended solids, total nitrogen, phosphates, carbon and silicates, improving stream water quality.<ref>{{cite journal |title=Beaver pond biogeochemical effects in the Maryland Coastal Plain |journal=Biogeochemistry |date=June 2000 |pages=217–239 |jstor=1469618 |author=Correll, David L.; Jordan, Thomas E. and Weller, Donald E. |volume=49 |issue=3 |doi=10.1023/A:1006330501887 }}</ref><ref name=Muskopf>{{cite thesis |title=The Effect of Beaver (Castor canadensis) Dam Removal on Total Phosphorus Concentration in Taylor Creek and Wetland, South Lake Tahoe, California |author=Muskopf, Sarah |publisher=Humboldt State University, Natural Resources |date = October 2007|url= |accessdate=February 27, 2011 }}</ref> In addition, fecal coliform and streptococci bacteria excreted into streams by grazing cattle are reduced by beaver ponds, where slowing currents lead to settling of the bacteria in bottom sediments.<ref name="Quentin D. Skinner, John E. Speck, Michael Smith, John C. Adams 142–146">{{cite journal |title=Stream Water Quality as Influenced by Beaver within Grazing Systems in Wyoming |journal=Journal of Range Management |date=March 1984 |pages=142–146 |jstor=3898902 |author=Skinner, Quentin D.; Speck, John E.; Smith, Michael and Adams, John C. |volume=37 |issue=2 |doi=10.2307/3898902 }}</ref>
The term "beaver fever" is a misnomer coined by the American press in the 1970s, following findings that the parasite ''[[Giardia lamblia]]'', which causes [[Giardiasis]], is carried by beavers. However, further research has shown that many animals and birds carry this parasite, and the major source of water contamination is by humans.<ref>{{cite journal |title=Reintroducing the European Beaver in Britain |journal=British Wildlife |year=2008 |url= |accessdate=March 26, 2011 |author=Gaywood, Martin; Batty, Dave and Galbraith, Colin }}</ref><ref>{{cite book |title= Waterborne giardiasis: sources of Giardia cysts and evidence pertaining to their implication in human infection in P. M. Wallis and B. R. Hammond (ed.), Advances in Giardia research. |year=1988 |pages=227–236 |publisher=University of Calgary Press |location=Calgary, Alberta, Canada |author=Erlandsen, S. L., and Bemrick, W. J. }}</ref><ref>{{cite journal |title=Prevalence of Giardia spp. in Beaver and Muskrat Populations in Northeastern States and Minnesota: Detection of Intestinal Trophozoites at Necropsy Provides Greater Sensitivity than Detection of Cysts in Fecal Samples |journal=Applied and Environmental Microbiology |date=January 1990 |pages=31–36 |url= |accessdate=March 26, 2011 |author=Erlandsen SL, Sherlock LA, Bemrick WJ, Ghobrial H, Jakubowski W |pmid=2178552 |volume=56 |issue=1 |pmc=183246 }}</ref> Recent concerns point to domestic animals as a significant vector of giardia with young calves in dairy herds testing as high as 100% positive for giardia.<ref>{{cite journal |title=Giardiasis as a re-emerging infectious disease and its zoonotic potential |author=Thompson, R. C. A. |journal=International Journal of Parasitology |date=November 2000 |pages=1259–1267|doi=10.1016/S0020-7519(00)00127-2 |volume=30 |issue=12–13 |pmid=11113253}}</ref> In addition, fecal coliform and streptococci bacteria excreted into streams by grazing cattle have been shown to be reduced by beaver ponds, where the bacteria are trapped in bottom sediments.<ref name="Quentin D. Skinner, John E. Speck, Michael Smith, John C. Adams 142–146"/> In fact, [[New Zealand]] has giardia outbreaks but no beaver, whereas [[Norway]] has plenty of beaver but had no giardia outbreaks until recently (in a southern part of Norway densely populated by humans but no beaver).<ref>{{cite journal |title=A large community outbreak of waterborne giardiasis-delayed detection in a non-endemic urban area |journal=BMC Public Health |year=2006 |url= |accessdate=November 26, 2011 |author=Nygård, Karin; Schimmer, Barbara; Søbstad, Øystein; Walde, Anna; Tveit, Ingvar; Langeland, Nina; Hausken, Trygve and Aavitsland, Preben }}</ref>
===Effects on bird abundance and diversity===
[[File:Canada Geese Nesting on Beaver Lodge, Crawford County, PA 1960.jpg|thumb|[[Canada Goose]] nest on beaver lodge |left]]
Beaver help waterfowl by creating increased areas of water, and in northerly latitudes they thaw areas of open water, allowing an earlier nesting season.<ref>{{cite journal |title=Beavers (Castor canadensis) facilitate early access by Canada geese (Branta canadensis) to nesting habitat and areas of open water in Canada's boreal wetlands |journal=Mammalian Biology |year=2013 |volume=78 |pages=73–77 |url= |accessdate=February 14, 2013 |author=Bromley, Chantal K. and Hood, Glynnis A. |issue=1 }}</ref> In a study of Wyoming streams and rivers, watercourses with beaver had 75-fold more ducks than those without.<ref>{{cite journal |title=The Importance of Beaver to Waterfowl and Wetlands Habitats in Wyoming |author=McKinstry, M. C.; Caffrey, P. and Anderson, S. H. |journal=Journal of the American Water Resources Association |year=2001|doi=10.1111/j.1752-1688.2001.tb03660.x |volume=37 |issue=6 |pages=1571}}</ref>
[[Trumpeter swan]]s (''Cygnus buccinator'') and [[Canada goose|Canada geese]] (''Branta canadensis'') often depend on beaver lodges as nesting sites.<ref name=Rosell /><ref>{{cite journal |title=Canada geese nesting on a beaver lodge |author=Brenner, F.J. |year=1960 |journal=The Auk |pages=476–477 |url= |accessdate=Mar 1, 2010 |doi=10.2307/4082428 |volume=77 |issue=4 }}</ref><ref>{{cite book |title=Trumpeter Swan (Cygnus buccinator). In The Birds of North America No. 105 |author=Mitchell, C.D. |year=1994 |editors=A. Poole and F. Gill |location=Philadelphia |publisher=The Academy of Natural Sciences |page=10 }}</ref> Canada's small trumpeter swan population was observed not to nest on large lakes, preferring instead to nest on the smaller lakes and ponds associated with beaver activity.<ref>{{cite journal |title=The Status and Distribution of Trumpeter Swans (Cygnus buccinator) in the Yukon |author=McKelvey RW, Denningtonz MC, Mossop |journal=Arctic |date=March 1983 |pages=76–81 |url= |accessdate=Mar 1, 2010 }}</ref><ref>{{cite book |title=Beavers, Water, Wildlife and History |author=Hilfiker, E.L. |year=1991 |page=198 |publisher=Windswept Press |location=Interlaken, New York |isbn=978-1-55787-067-4 }}</ref>
Beaver may benefit the birds frequenting their ponds in several additional ways. Removal of some pondside trees by beavers would increase the density and height of the grass–forb–shrub layer, which enhances waterfowl nesting cover adjacent to ponds.<ref>{{cite journal |doi=10.1111/j.1365-2907.2005.00067.x |title=Ecological impact of beavers Castor fibre and Castor canadensis and their ability to modify ecosystems |author=Rosell, Frank; Bozser, Orsolya; Collen, Peter and Parker, Howard |journal=Mammal Review |volume=35 |page=248 |year=2005 |issue=3–4 }}</ref> Both forest gaps where trees had been felled by beaver and a "gradual edge" described as a complex transition from pond to forest with intermixed grasses, forbs, saplings, and shrubs are strongly associated with greater migratory bird species richness and abundance.<ref>{{cite journal |doi=10.1676/04-116.1 |title=The Use of Southern Appalachian Wetlands by Breeding Birds, with a Focus on Neotropical Migratory Species |author= Bulluck, Jason F. and Rowe, Matthew P. |journal=The Wilson Journal of Ornithology |volume=118 |page=399 |year=2006 |issue=3 }}</ref> [[Coppicing]] of waterside willows and cottonwoods by beavers leads to dense shoot production which provides important cover for birds and the insects they feed on.<ref>{{cite journal |title=Management by Assertion: Beavers and Songbirds at Lake Skinner (Riverside County, California) |author=Longcore, Travis; Rich, Catherine and Muller-Schwarze, Dietland |journal=Environmental Management |date=February 2007 |pages= 460–471 |doi=10.1007/s00267-005-0204-4 }}</ref> Widening of the riparian terrace alongside streams is associated with beaver dams and has been shown to increase riparian bird abundance and diversity, an impact that may be especially important in semi-arid climates.<ref>{{cite journal |title=Influence of Beaver Dam Density on Riparian Areas and Riparian Birds in Shrubsteepe of Wyoming |journal=Western North American Naturalist |year=2008 |volume=68 |issue=3 |pages=365–373 |url= |accessdate=February 16, 2013 |author=Cooke, Hilary A. and Zack, Steve |doi=10.3398/1527-0904(2008)68[365:IOBDDO]2.0.CO;2 }}</ref>
As trees are drowned by rising beaver impoundments they become ideal nesting sites for woodpeckers, who carve cavities that attract many other bird species including [[Empidonax|flycatchers]] (''Empidonax spp.''), [[tree swallow]]s (''Tachycineta bicolor''), [[tit (bird)|tits]] (''Paridae spp.''), [[wood duck]]s (''Aix sponsa''), [[goldeneye (duck)|goldeneye]]s (''Bucephala spp.''), [[merganser]]s (''Mergus spp.''), [[owl]]s (''Titonidae'', ''Strigidae'') and [[American kestrel]]s (''Falco sparverius'').<ref name=Rosell /> Piscivores, including [[heron]]s (''Ardea spp.''), [[grebe]]s (''Podicipedidae''), [[cormorant]]s (''Phalacrocorax ssp.''), [[American bittern]]s (''Botaurus lentiginosa''), [[great egret]] (''Ardea alba''), [[snowy egret]] (''Egretta thula''), mergansers and [[belted kingfisher]]s (''Megaceryle alcyon''), utilize beaver ponds for fishing. [[Hooded merganser]]s (''Lophodytes cucullatus''), [[green heron]] (''Butorides virescens''), [[great blue heron]] (''Ardea herodias'') and belted kingfisher occurred more frequently in New York wetlands where beaver were active than at sites with no beaver activity.<ref>{{cite journal |title=Bird species richness within beaver ponds in south-central New York |author=Grover, A.M. & Baldassarre, G.A. |year=1995 |journal=Wetlands |pages=108–118|doi=10.1007/BF03160664 |volume=15 |issue=2 }}</ref>
===Effects on trout and salmon===
[[File:Sockeye salmon jumping over beaver dam Lake Aleknagik, AK Kristina Ramstad 1997.jpg|thumb|upright|[[Salmon]] (''[[Oncorhynchus nerka]]'') jumping beaver dam |right]]
====Beaver ponds as rearing habitat for salmonids====
Beaver ponds have been shown to have a beneficial effect on trout and salmon populations. In fact, many authors believe that the decline of salmonid fishes is related to the decline in beaver populations. Research in the [[Stillaguamish River]] basin in [[Washington (U.S. state)|Washington]] state, found that extensive loss of beaver ponds resulted in an 89% reduction in [[coho salmon]] (''Oncorhynchus kisutch'') smolt summer production and an almost equally detrimental 86% reduction in critical winter habitat [[carrying capacity]].<ref name=Stillaguamish>{{cite journal |title=The Importance of Beaver Ponds to Coho Salmon Production in the Stillaguamish River Basin, Washington, USA |author=Pollock, M. M.; Pess, G. R. and Beechie, T. J. |journal=North American Journal of Fisheries Management |pages=749–760 |year=2004 |url= |accessdate=Feb 28, 2010 |doi=10.1577/M03-156.1 |volume=24 |issue=3 }}</ref> This study also found that beaver ponds increased smolt salmon production 80 times more than the placement of large woody debris.<ref name=Stillaguamish/> Swales and Leving had previously shown on the [[Coldwater River (British Columbia)|Coldwater River]] in [[British Columbia]] that off-channel beaver ponds were preferentially populated by coho salmon over other salmonids and provided overwintering protection, protection from high summer snowmelt flows and summer coho rearing habitat.<ref>{{cite journal |title=Role of Off-Channel Ponds in the life Cycle of Coho Salmon (Oncorhynchus kisutch) and Other Juvenile Salmonids in the Coldwater River, British Columbia |journal= Canadian Journal Fisheries Aquatic Sciences| volume = 46 |year=1989 |pages=232–242 |doi=10.1139/f89-032 |author= Swales, S. and Levings, C. D. |issue=2}}</ref> The presence of beaver dams has also been shown to either increase the number of fish, their size, or both, in a study of [[brook trout]] (''Salvelinus fontinalis''), [[rainbow trout]] (''Oncorhynchus mykiss'') and [[brown trout]] (''Salmo trutta'') in [[Sagehen Creek]], which flows into the [[Little Truckee River]] at an altitude of 5,800 feet in the northern [[Sierra Nevada (U.S.)|Sierra Nevada]].<ref name=Gard>{{cite journal |title=Effects of beaver on trout in Sagehen Creek, California |author=Gard R |year=1961 |journal= Journal of Wildlife Management |volume=25 |issue=3 |pages=221–242 |jstor=3797848 |doi=10.2307/3797848 }}</ref> These findings are consistent with a study of small streams in [[Sweden]], that found that brown trout were larger in beaver ponds compared with those in [[riffle]] sections, and that beaver ponds provide habitat for larger trout in small streams during periods of drought.<ref>{{cite journal |title=Effects of beaver dams on the fish fauna of forest streams |author=Hägglund, Å. & Sjöberg, G. |year=1999 |journal=Forest Ecology and Management |pages=259–266|doi=10.1016/S0378-1127(98)00404-6 |volume=115 |issue=2–3}}</ref> Similarly, brook trout, coho salmon and [[sockeye salmon]] (''Oncorhynchus nerka'') were significantly larger in beaver ponds than those in un-impounded stream sections in [[Colorado]] and [[Alaska]].<ref>{{cite journal |title=Wildlife and environmental relationships of beavers in Colorado forests |author=Rutherford, W.H. |year=1955 |journal=Journal of Forestry |pages=803–806 |url=;jsessionid=2k4r9ihuef8i6.alice |accessdate=Feb 28, 2010 }}</ref><ref>{{cite journal |title=Habitat utilisation by juvenile Pacific salmon (Onchorynchus) in the glacial Taku River, southeast Alaska |author=Murphy, M.L., Heifetz, J., Thedinga, J.F., Johnson, S.W. & Koski, K.V. |year=1989 |journal=Canadian Journal of Fisheries and Aquatic Science |pages=1677–1685 |doi=10.1139/f89-213 |volume=46 |issue=10 }}</ref> In a recent study on a headwater Appalachian stream, brook trout were also larger in beaver ponds.<ref>{{cite journal |title=Short-Term Effects of Beaver Dam Removal on Brook Trout in an Appalachian Headwater Stream |authors=J. M. Niles, K. J. Hartman, and P. Keyser |journal=Northeastern Naturalist |year=2013 |volume=20 |issue=3 |pages=540–551 |url= |accessdate=2013-11-17 }}</ref>
====Beaver ponds are generally not barriers to trout and salmon passage====
Contrary to popular myth, most beaver dams do not pose barriers to trout and salmon migration, although they may be restricted seasonally during periods of low stream flows.<ref name=Pollock>{{cite journal |title=Hydrologic and Geomorphic Effects of Beaver Dams and Their Influence on Fishes |author=Pollock, Michael M.; Heim, Morgan and Werner, Danielle |journal=American Fisheries Society Symposium 37 |year=2003 |url= |accessdate=Jan 17, 2010 }}</ref> In a meta-review of studies claiming that beaver dams act as fish passage barriers Kemp et al. found that 78% of these claims were not supported by any data.<ref name=metareview/> In a 2013 study of radiotelemetry-tagged [[Bonneville cutthroat trout]] (''Oncorhynchus clarki utah'') and [[brook trout]] (''Salvelinus fontinalis'') in Utah, both of these fish species crossed beaver dams in both directions, including dams up to {{convert|2|m|ft}} high.<ref>{{cite journal |title=Do Beaver Dams Impede the Movement of Trout? |authors=Ryan L. Lokteff, Brett B. Roper, Joseph M. Wheaton |journal=Transactions of the American Fisheries Society |year=2013 |url= |accessdate=2013-12-23 }}</ref> Rainbow, brown and brook trout have been shown to cross as many as 14 consecutive beaver dams.<ref name=Gard /> Both adults and juveniles of coho salmon, [[steelhead trout]], [[Coastal cutthroat trout|sea run cutthroat]] (''Oncorhyncus clarki clarki''), [[Dolly Varden trout]] (''Salvelinus malma malma''), and sockeye salmon are able to cross beaver dams.<ref name=Pollock /> In southeast Alaska, coho jumped dams as high as 2 meters, were found above all beaver dams and had their highest densities in streams with beaver.<ref>{{cite journal |title=The Role of Beaver Dams as Coho Salmon Habitat in southeast Alaska Streams |author=Bryant, M. D. |year=1984 |editors=Walton, J.M. and Houston, D.B.|journal=Proceeding, Olympic Wild Fish Conferences |pages=183–192 |publisher=Peninsula College, Fisheries Technology program |location=Port Angeles, Washington }}</ref> In Oregon coastal streams, beaver dams are ephemeral and almost all wash out in high winter flows only to be re-built every summer.<ref>{{cite journal |title=Beaver Dam Locations and Their Effects on Distribution and Abundance of Coho Salmon Fry in Two Coastal Oregon Streams |journal=Northwest Science |year=1992 |url= |accessdate=April 16, 2011 |author=Leidholt-Bruner, Karen; Hibbs, David E. and McComb, William C. }}</ref> Migration of adult [[Atlantic salmon]] (''Salmo salar'') may be limited by beaver dams but the presence of juveniles upstream from the dams suggests that the dams are penetrated by [[Parr (fish)|parr]].<ref name=Collen>{{cite journal |title=The general ecology of beavers (Castor spp.), as related to their influence on stream ecosystems and riparian habitats, and the subsequent effects on fish&nbsp;– a review |author=Collen P, Gibson RJ |journal=Reviews in Fish Biology and Fisheries |pages=439–461 |year=2001 |url= |accessdate=Mar 2, 2010 }}</ref> Downstream migration of Atlantic salmon smolts was similarly unaffected by beaver dams, even in periods of low flows.<ref name=Collen /> Two year old Atlantic salmon parr in beaver ponds in eastern Canada showed faster summer growth in length and mass and were in better condition than parr upstream or downstream from the pond.<ref>{{cite journal |title=Influence of Beaver Activity on Summer Growth and Condition of Age-2 Atlantic Salmon Parr |author=Sigourney, D. B.; Letcher, B. H. and Cunjak, R. A. |journal=Transactions of the American Fisheries Society |volume=135 |year=2006 |pages=1068–1075 |doi=10.1577/T05-159.1 |issue=4 }}</ref>
====Beaver ponds play an important role in winter survival of salmonids====
The importance of winter habitat to salmonids afforded by beaver ponds may be especially important (and underappreciated) in streams without deep pools or where ice cover makes contact with the bottom of shallow streams. Enos Mills wrote in 1913, "One dry winter the stream...ran low and froze to the bottom, and the only trout in it that survived were those in the deep holes of beaver ponds."<ref>{{cite book |title=In Beaver World |author=Mills, Enos A. |year=1913|url=|publisher=Kessinger Publishing |page=280 |isbn=978-0-7661-9387-1 }}</ref> [[Cutthroat trout]] (Oncorhynchus clarki) and [[bull trout]] (Salvelinus confluentus) were noted to overwinter in Montana beaver ponds, brook trout congregated in winter in New Brunswick and Wyoming beaver ponds, and coho salmon in Oregon beaver ponds.<ref name=Collen /> In 2011 a meta-analysis of studies of beaver impacts on salmonids found that beaver were a net benefit to salmon and trout populations primarily by improving habitat (building ponds) both for rearing and overwintering and that this conclusion was based over half the time on scientific data. In contrast, the most often cited negative impact of beavers on fishes were barriers to migration although that conclusion was based on scientific data only 22% of the time. They also found that when beaver dams do present barriers that these are generally short-lived, as the dams are overtopped, blown out, or circumvented by storm surges.<ref name=metareview>{{cite journal |title=Qualitative and quantitative effects of reintroduced beavers on stream fish |journal=Fish and Fisheries |date=June 2011 |doi=10.1111/j.1467-2979.2011.00421.x |author=Kemp, Paul S.; Worthington, Tom A.; Langford, Terence E. L.; Tree, Angus R. J. and Gaywood, Martin J. |volume=13 |issue=2 |pages=158}}</ref>
====Beavers create channel complexity important to salmonid survival====
By creating additional channel network complexity, including ponds and marshes laterally separated from the main channel, beavers may play a role in the creation and maintenance of fish biodiversity.<ref>{{cite journal |title=The River Discontinuum: Applying Beaver Modifications to Baseline Conditions for Restoration of Forested Headwaters |journal=BioScience |volume=60 |issue=11 |pages=908–922 |year=2010 |author=Burchsted, Denise; Daniels, Melinda; Thorson, Robert and Vokoun, Jason |doi=10.1525/bio.2010.60.11.7 }}</ref> In off-mainstem channels restored by beaver on the middle section of Utah's [[Provo River]], native fish species persist even when they have been extirpated in the mainstem channel by competition from introduced non-native fish.<ref>{{cite journal |title=Habitat enhancement and native fish conservation: can enhancement of channel complexity promote the coexistence of native and introduced fishes? |author=Eric J. Billman, Joshua D. Kreitzer, J. Curtis Creighton, Evelyn Habit, Brock McMillan, and Mark C. Belk |journal=Environmental Biology of Fishes |year=2013 |volume=96 |pages=555–566 |url= |accessdate=2013-06-13 }}</ref> Efforts to restore salmonid habitat in the western United States have focused primarily on establishing [[large woody debris]] in streams to slow flows and create pools for young salmonids. However research in [[Washington (U.S. state)|Washington]] state found that the average summer smolt production per beaver dam ranges from 527 to 1,174 fish, whereas the summer smolt production from a pool formed by instream large woody debris is about 6–15 individuals, suggesting that re-establishment of beaver populations would be 80 times more effective.<ref name=Stillaguamish/>
====Beavers live in tidal estuaries and may impact fish in estuarine systems====
Recently, beaver have been discovered living in brackish water in estuarine tidal marshes, where [[Chinook salmon]] (''Oncorhynchus tshawytscha'') densities were five times higher in beaver ponds than in neighboring areas.<ref name=skagit/><ref>{{cite web |title=An Overlooked Ecological Web: Sweetgale, Beaver, Salmon, and Large Woody Debris in the Skagit River Tidal Marshes |author=Hood, W. Gregory |year=2009 |publisher=Skagit River Cooperative |url= |accessdate=June 22, 2010 }}</ref>
===Effects on riparian trees and vegetation===
[[File:Tree felled by beaver (Castor canadensis).JPG|thumb|right|Tree felled by beaver (''C. c. canadensis''), diameter 20&nbsp;cm]]
Conventional wisdom has held that beaver girdle and fell trees and that they diminish riparian trees and vegetation, but the opposite appears to be true when studies are conducted longer-term. In 1987, Beier reported that beaver had caused local extinction of [[Quaking aspen]] (''Populus tremuloides'') and [[Black cottonwood]] (''Populus trichocarpa'') on 4–5% of stream reaches on the lower [[Truckee River]] in the [[Sierra Nevada (U.S.)|Sierra Nevada]] mountains, however [[Willow]] (''Salix spp.'') responded by re-growing vigorously in most reaches. He further speculated that without control of beaver populations that aspen and cottonwood could go extinct on the Truckee River.<ref>{{cite journal |title=Beaver Habitat Use and Impact in Truckee River Basin, California |author=Beier, Paul and Barrett, Reginald H. |journal=Journal of Wildlife Management |year=1987 |volume=51 |issue=4 |pages=794–799 |jstor=3801743 |doi=10.2307/3801743 }}</ref> However, not only have aspen and cottonwood survived ongoing beaver colonization but a recent study of ten Sierra Nevada streams in the [[Lake Tahoe]] basin utilizing aerial multispectral videography has shown that deciduous, thick herbaceous, and thin herbaceous vegetation are more highly concentrated near beaver dams, whereas coniferous trees are decreased.<ref name=Ayers>{{cite thesis |title=Aerial Multispectral Videography for Vegetation Mapping and Assessment of Beaver Distribution within Selected Riparian Areas of the Lake Tahoe Basin |author=Benson Ayers, Michael |date=1997 |pages=71 |publisher=University of Nevada at Reno |url= |accessdate=August 26, 2010 }}</ref> These findings are consistent with those of Pollock, who reported that in [[Bridge Creek (John Day River)|Bridge Creek]], a stream in semi-arid eastern Oregon, the width of riparian vegetation on stream banks was increased several-fold as beaver dams watered previously dry terraces adjacent to the stream.<ref>{{cite journal |doi=10.1002/esp.1553/pdf |title=Geomorphic changes upstream of beaver dams in Bridge Creek, an incised stream channel in the interior Columbia River basin, eastern Oregon |author=Pollock, Michael M.; Beechie, Timothy J. and Jordan, Chris E. |journal=Earth Surface Processes and Landforms |year=2007 }}</ref> In a second study of riparian vegetation based on observations of Bridge Creek over a 17 year time period, although portions of the study reach were periodically abandoned by beaver following heavy utilization of streamside vegetation, within a few years dense stands of woody plants of greater diversity occupied a larger portion of the floodplain. Although black cottonwood and thinleaf alder did not generally re-sprout after beaver cutting, they frequently grew from seeds landing on freshly exposed alluvial deposits secondary to beaver activity.<ref>{{cite journal |title=Recent History (1988–2004) of Beaver Dams along Bridge Creek in Central Oregon |journal=Northwest Science |date=September 2008 |doi=10.3955/0029-344X-82.4.309 |author=Demmer, Rick and Beschta, Robert L. |volume=82 |issue=4 |pages=309–318}}</ref> Therefore, beaver appear to increase riparian vegetation given enough years to aggrade sediments and pond heights sufficiently to create widened, well-watered riparian zones, especially in areas of low summer rainfall.
The surface of beaver ponds are typically at or near bank-full, so even small increases in stream flows cause the pond to overflow its banks. Thus, high stream flows spread water and nutrients to beyond the stream banks to wide riparian zones when beaver dams are present.
===Beavers and stream restoration===
In the 1930s, the U.S. Government put 600 beaver to work alongside the [[Civilian Conservation Corps]] in projects to stop soil erosion by streams in Oregon, Washington, Wyoming, and Utah. At the time it was estimated that each beaver, whose initial cost was about $5, completed work worth $300.<ref>{{cite journal |title=Beaver-Dams as Geologic Agents |journal=Science |date=December 2, 1938 |pages=523–525 |doi=10.1126/science.88.2292.523 | bibcode=1938Sci....88..523R |author=Ruedemann, Rudolf and Schoonmaker, W. J. |volume=88 |issue=2292 |pmid=17840531 }}</ref>
In a pilot study in [[Washington (U.S. state)|Washington state]], the Lands Council is reintroducing beavers to evaluate their projections that if 10,000 miles of suitable habitat were repopulated then 650 trillion gallons of spring runoff would be held back for release in the arid fall season.<ref>{{cite journal |title=Beavers Sign up to Fight Effects of Climate Change |author=Groc, Isabelle |journal=Discover |date=April 19, 2010 |url= |accessdate=July 27, 2010 }}</ref> This project was developed in response to a 2003 [[Washington Department of Ecology]] proposal to spend as much as ten billion dollars on construction of several dams on [[Columbia River]] tributaries to retain storm season runoff.<ref>{{cite web |title=The Beaver Solution: Solving our Water Storage Dilemma in Eastern Washington |publisher=The Lands Council |date=March 2010 |url= |accessdate=July 27, 2010 }}</ref> The State of [[Utah]] published a Beaver Management Plan which includes re-establishing beavers in ten streams per year for the purpose of watershed restoration each year from 2010 through 2020.<ref>{{cite report |title=Utah Beaver Management Plan |publisher=[[Utah Division of Wildlife Resources]] |date=January 6, 2010 |pages=25 |url= |accessdate=August 29, 2010 }}</ref>
==Urban beavers==
[[File:Lincoln Park Beaver Facebook Lindsay Fox Sept. 2008.jpg|thumb |left|Beaver before being drowned by trapper's snare in Lincoln Park, Chicago 2008]]
[[File:Lincoln Park North Pond Beaver Lodge Dec 4, 2009.jpg|thumb |left |After trapping, beaver lodge re-appears in Lincoln Park, Chicago Fall, 2009]]
After 200 years, a beaver returned to [[New York City]] in 2007, making its home along the [[Bronx River]], having spent time living at the [[Bronx Zoo]] as well as the Botanical Gardens.<ref>{{cite news |title=New York City Beaver Returns |newspaper=Science Daily |url= |date=December 20, 2008 }}</ref> Beavers have not lived in New York City since the early 19th century when trappers extirpated them completely from the state.<ref>{{cite journal |title=Manhattan Before New York: When Henry Hudson first looked on Manhattan in 1609, what did he see? |author=Miller, Peter |url= |journal=National Geographic |date=September 2009 }}</ref> The return of "José", named after Representative [[José Enrique Serrano|Jose Serrano]] from the Bronx, has been seen as evidence that efforts to restore the river have been successful.<ref>{{cite news |title=After 200 Years, a Beaver Is Back in New York City |author=O'Connor, Anahad |newspaper=New York Times |date=February 23, 2007 |url= |accessdate=Dec 4, 2009 }}</ref><ref>Trotta, Daniel. [ "Beaver Returns to New York City After 200 Years."] ''World Environment News.'' Dec 26, 2007.</ref><ref>{{cite web |title=Bronx River Crossing |author=Design Trust for Public Space |date=June 17, 2009 |url= |accessdate=Dec 4, 2009 }}</ref> In the summer of 2010 a second beaver name "Justin" joined José, doubling the beaver population in New York City.<ref>{{cite news |title=Another beaver makes Bronx River home&nbsp;– doubles total beaver population |author=Paddock, Barry |newspaper=New York Daily News |date=September 19, 2010 |url= |accessdate=September 19, 2010 }}</ref> In February 2013 what appears to be both José and Justin were caught on motion-sensitive cameras at the [[New York Botanical Garden]].<ref>{{cite news |title=Beaver Gets Busy at Botanical Garden |author=Newman, Andy |date=February 7, 2013 |newspaper=New York Times |url= |accessdate=February 13, 2013 }}</ref> Beaver were once important to the city's economy and a pair of beavers appears on the city's official seal and flag.
In [[Chicago]], several beavers have returned and made a home near the [[Lincoln Park]]'s North Pond. The "[[Lincoln Park Beaver]]" has not been as well received by the [[Chicago Park District]] and the [[Lincoln Park]] Conservancy, which was concerned over damage to trees in the area. In March 2009, they hired an exterminator to remove a beaver family using live traps, and accidentally killed the mother when she got caught in a snare and drowned.<ref name="Inside">{{cite news |author=Boehm, Kiersten |title=Lincoln Park Beaver Relocated |newspaper=Inside at Your News Chicago, IL Edition |date=Nov 14, 2008 |url= |accessdate=Dec 4, 2009 }}</ref> Relocation costs $4,000–$4,500 per animal. Scott Garrow, District Wildlife Biologist with the [[Illinois Department of Natural Resources]], opined that relocating the beavers may be "a waste of time", as there are records of beaver recolonizing North Pond in Lincoln Park in 1994, 2003, 2004, 2008 and 2009.<ref name="Inside" /><ref>{{cite book |title=Tales from an Urban Wilderness: Wildlife's Struggle for Survival in a Park Where City & Wilderness Meet |author=Holingue, Scott |publisher=Chicago Historical Bookworks |location=Chicago, IL |date=Jan 1, 1994 |page=140 |isbn=0-924772-25-5 }}</ref><ref name="">{{cite news |title=Park District Kills Beaver in Lincoln Park |date=April 2009 |newspaper=MyFoxChicago|url= |accessdate=December 4, 2009 }}</ref><ref>{{cite news |title=Why are there signs that claim the Park District murdered a beaver? |author=Greenfield, John |url= |newspaper=Time Out Chicago |date=May 7–13, 2009 |accessdate=Dec 4, 2009}}</ref> As of fall 2009 a new beaver lodge has appeared on North Pond's northwest bank.
Outside [[San Francisco]], in downtown [[Martinez, California]], a male and female beaver arrived in [[Alhambra Creek]] in 2006.<ref>{{cite web |title=Moment of truth for Martinez beavers |author=Jones, Carolyn |work=San Francisco Chronicle |url= |date=April 16, 2008}}</ref> The [[Martinez beavers]] built a dam 30 feet wide and at one time 6 feet high, and chewed through half the willows and other creekside landscaping the city planted as part of its $9.7 million 1999 flood-improvement project. When the City Council wanted to remove the beavers because of fears of flooding, local residents organized to protect them, forming an organization called "Worth a Dam".<ref>{{cite web |title=Worth a Dam website|url= }}</ref> Resolution included installation of a [[flow device]] through the [[beaver dam]] so that the pond's water level could not become excessive. Now protected, the beaver have transformed Alhambra Creek from a trickle into multiple dams and beaver ponds, which in turn, led to the return of [[steelhead trout]] and [[North American river otter|river otter]] in 2008, and [[mink]] in 2009.<ref>{{cite journal |title=Martinez Beavers |author=George, Aleta |url= |year=2008 |magazine=Bay Nature |publisher=Bay Nature Institute |accessdate=Nov 6, 2009 }}</ref><ref>{{cite journal |title=Beavers and More in Martinez:New Habitat Thanks to Beavers |author=DeRobertis-Theye, Nicola |url= |magazine=Bay Nature |publisher=Bay Nature Institute |accessdate=Nov 6, 2009 }}</ref> The Martinez beavers probably originated from the [[Sacramento-San Joaquin River Delta]] which once held the largest concentration of beaver in North America.<ref>{{cite book |title=Life, adventures, and travels in California |author=Farnham, Thomas Jefferson |page=383 |publisher=Blakeman & Co. |year=1857 |url=}}</ref>
In 1999, [[Washington, D.C.]]'s annual [[National Cherry Blossom Festival|Cherry Blossom Festival]] was plagued by a family of beavers who lived in the [[Tidal Basin]]. The offenders were caught and removed, but not before damaging 14 cherry trees, including some of the largest and oldest trees.<ref>{{cite news |title= Beaver is bad guy at cherry blossom time |author=Aiken, Jonathan |date=April 7, 1999 | |accessdate=Nov 22, 2009 |url= }}</ref><ref>{{cite news |title=Beaver Chomps Into Cherry Blossom Season |author=Wheeler, Linda |newspaper=Washington Post |date=April 7, 1999 |url= |accessdate=Nov 22, 2009 }}</ref>
==As introduced non-native species==
{{See also|Beaver eradication in Tierra del Fuego}}
[[File:beaver damage navarino chile.JPG|thumb|right|Beaver damage on the north shore of Robalo Lake, [[Navarino Island]], [[Chile]]]]
In the 1940s, beavers were brought to the island of [[Tierra Del Fuego]] in southern [[Chile]] and [[Argentina]] for commercial fur production and introduced near [[Cami Lake|Fagnano Lake]]. Although the fur enterprise failed, 25 mating pairs of beavers were released into the wild. Having no natural predators in their new environment, they quickly spread throughout the island, and to other islands in the region, reaching a number of 100,000 individuals within just 50 years. Although they have been considered an [[invasive species]], it has been more recently shown that the beaver have some beneficial ecological effects on native fish and should not be considered wholly detrimental.<ref name=Anderson>{{cite journal |title=Do introduced North American beavers Castor canadensis engineer differently in southern South America? An overview with implications for restoration |journal=Mammalian Review |year=2009 |url= |accessdate=March 17, 2012 |author=Anderson, Christopher B.; Pastur, Guillermo Martinez; Lencinas, Maria Vanessa; Wallem, Petra K.; Moorman, Michelle C. and Rosemond, Amy D. }}</ref> Although the dominant [[Nothofagus pumilio|Lenga beech]] (''Nothofagus pumilio'') forest can regenerate from stumps, most of the newly created beaver wetlands are being colonized by the rarer native [[Nothofagus antarctica|Antarctic beech]] (''Nothofagus antarctica''). It is not known whether the shrubbier Antarctic beech will be succeeded by the originally dominant and larger Lengo beech, however, and the beaver wetlands are readily colonized by non-native plant species.<ref name=Anderson/> In contrast, areas with introduced beaver were associated with increased populations of the native [[catadromous]] [[Common galaxias|puye]] fish (''Galaxias maculatus'').<ref>{{cite journal |title=Ictiofauna en los sistema límnicos de la Isla Grande, Tierra del Fuego, Chile |year=1999 |journal=Revista Chilena de Historia Natural |pages=273–284 |author=Vila, I., Fuentes, L.S. & Saavedra, M.|url= }}</ref><ref name=Moorman>{{cite journal |doi=10.1577/T08-081.1 |title=Implications of Beaver Castor canadensis and Trout Introductions on Native Fish in the Cape Horn Biosphere Reserve, Chile |author=Moorman, Michelle C.; Eggleston, David B.; Anderson, Christopher B.; Mansilla, Andres and Szejner, Paul |journal=Transactions of the American Fisheries Society |volume=138 |year=2009 |pages=306–313 |issue=2 }}</ref> Furthermore, the beavers did not seem to have a highly beneficial impact on the exotic [[brook trout]] (''Salvelinus fontinalis'') and [[rainbow trout]] (''Oncorhynchus mykiss'') which have negative impacts on native stream fishes in the [[Cape Horn Biosphere Reserve]], [[Chile]].<ref name=Moorman/> They have also been found to cross saltwater to islands northward; and reached the Chilean mainland in the 1990s.<ref>{{cite journal |title=Identificación de los mecanismo subyacentes a la invasión de Castor canadensis (Kuhl 1820, Rodentia) en el archipiélago de Tierra del Fuego, Chile |year=2007 |journal=Revista Chilena de Historia Natural |pages=309–325 |author=Wallem, P.K., Jones, C.G., Marquet, P.A. & Jaksic, F.M. }}</ref> On balance, because of their landscape-wide modifications to the Fuegian environment and because biologists want to preserve the unique biota of the region, most favor their removal.<ref>{{cite news| url= | work=CNN | title=Argentina eager to rid island of beavers | accessdate=May 20, 2010}}</ref>
==As food==
Beaver meat is similar tasting to lean [[beef]], but care must be taken to prevent contamination from the animal's strong castor ([[musk]]) gland. It is usually slow-cooked in a broth, and was a valuable food source to [[Indigenous peoples of the Americas|Native Americans]].{{Citation needed|date=January 2008}} Early French Canadian Catholics considered beaver to be "four-legged fish" that could be eaten at Lent.<ref>{{cite web |title=Our symbolic beaver overcomes challenges of past |author=Poirier, Nelson |publisher=Times & Transcript |date=November 27, 2010 |location=Moncton, New Brunswick |url= |accessdate=November 18, 2010 }}</ref>
Despite their name, the fried pastries found in parts of Canada called [[Beaver tail (pastry)|beaver tails]] contain no beaver.
[[File:Beaver sculpture, Centre Block.jpg|thumb|Beaver sculpture over entrance to Canadian Parliament Building]]
As the national animal and one of the national symbols of Canada,<ref name=HC>[ The Beaver] Heritage Canada</ref> the beaver is depicted on the [[Nickel (Canadian coin)|Canadian five-cent piece]]<ref name=HC/> and was on the first Canadian postage stamp, the Three Penny Beaver. It is also the state animal of [[Oregon]] and [[New York State|New York]], and a common school emblem for [[engineering]] schools, including the [[California Institute of Technology]], the [[Massachusetts Institute of Technology]], and the [[University of Alberta]] as well as the mascot for [[Oregon State University]], [[Babson College]], and the [[City College of New York]]. The beaver also appears in the [[coat of arms|coats of arms]] of the [[Hudson's Bay Company]],<ref>[ The HBC Coat of Arms], Hbc Heritage</ref> [[University of Toronto]], [[Wilfrid Laurier University]], and the [[London School of Economics]].
Much of the early economy of [[New Netherland]] was based on the beaver [[fur trade]]. As such, the seal of New Netherland featured the beaver; likewise, the coats of arms of [[Coat of arms of Albany, New York|Albany, New York]] and [[Seal of New York City|New York City]] included the beaver.
==See also==
* [[Beaver in the Sierra Nevada]]
==Further reading==
* {{ITIS |id=180212 |taxon=Castor canadensis |accessdate=March 18, 2006}}
* {{cite book |title=The beaver: natural history of a wetlands engineer |page=190 |publisher=Cornell University Press |year=2003 |isbn=978-0-8014-4098-4|author=Müller-Schwarze, Dietland and Sun, Lixing }}
* {{cite book|last=Mills|first=Enos|title=In Beaver World |publisher=Kessinger Publishing |page=255 |year=1913 |isbn=978-0-7661-9387-1}}
* {{cite book|last=Collier|first=Eric|title=Three Against the Wilderness|page=288 |publisher=Touchwood Editions|year=2007|isbn=978-1-894898-54-6}}
* {{cite book|last=Long|first=Kim|title=Beavers: A Wildlife Handbook|publisher=Johnson Books|location=Boulder|year=2000|isbn=1-55566-251-X|page=37}}
==External links==
{{commons|Castor canadensis}}
{{wikispecies|Castor canadensis}}
* [ Ecology of the Beaver]
* [ The romance of the beaver;] being the history of the beaver in the western hemisphere, by A. Radclyffe Dugmore. Illustrated with photographs from life and drawings by the author. Publisher: Philadelphia, J.B. Lippincott company; London, W. Heinemann 1914 ''(a searchable facsimile at the University of Georgia Libraries)''
* [ "Worth a Dam" (beaver information and educational site)]
* [ The Beaver A Keystone Species, a short video by Mike Foster ]
* [ Video Eager Beavers Take on Climate Change: Restoring Nature's Engineers in Utah by Grand Canyon Trust ]
{{DEFAULTSORT:Beaver, American}}
[[Category:Beavers|American Beaver]]
[[Category:Fur trade]]
[[Category:Mammals of North America]]
[[Category:Mammals of Canada]]
[[Category:Mammals of the United States]]
[[Category:Mammals of Mexico]]
[[Category:Fauna of the Rocky Mountains]]
[[Category:Fauna of the Great Lakes region (North America)]]
[[Category:Fauna of the Eastern United States]]
[[Category:Fauna of the Western United States]]
[[Category:National symbols of Canada]]
[[Category:Symbols of Oregon]]
[[Category:Invasive mammal species]]
[[Category:Megafauna of North America]]
[[Category:Animals described in 1820]]
{{Link FA|he}}
Reason: ANN scored at 0.93311
Reporter Information
Reporter: Bradley (anonymous)
Date: Wednesday, the 21st of October 2015 at 04:49:51 PM
Status: Reported
Wednesday, the 21st of October 2015 at 04:49:51 PM #101590
Bradley (anonymous)