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Brief Summary

    North American beaver: Brief Summary
    provided by wikipedia

    The North American beaver (Castor canadensis) is one of two extant beaver species. It is native to North America and introduced to Patagonia in South America and some European countries (e.g. Finland). 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 and Canadian beaver, distinguish this species from the other extant beaver species, Castor fiber, which is native to Eurasia. The North American beaver is an official animal symbol of Canada and is the official state mammal of Oregon.

Comprehensive Description

    North American beaver
    provided by wikipedia

    The North American beaver (Castor canadensis) is one of two extant beaver species.[22] It is native to North America and introduced to Patagonia in South America and some European countries (e.g. Finland). 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[22] and Canadian beaver,[27] distinguish this species from the other extant beaver species, Castor fiber, which is native to Eurasia. The North American beaver is an official animal symbol of Canada and is the official state mammal of Oregon.[28]

    Description

    This beaver is the largest rodent in North America and competes with its Eurasian counterpart, the European beaver, for being the second-largest in the world, both following the South American capybara. The European species is slightly larger on average but the American has a larger known maximum size. Adults usually weigh from 11 to 32 kg (24 to 71 lb), with 20 kg (44 lb) being typical. In New York, the average weight of adult male beavers was 18.9 kg (42 lb), while non-native females in Finland averaged 18.1 kg (40 lb). However, adults of both sexes averaged 16.8 kg (37 lb) in Ohio.[29][30][31] The species seems to conform to Bergmann's rule, as northern animals appear to be larger. In the Northwest Territory, adults weighed a median of 20.5 kg (45 lb).[32] The American beaver is slightly smaller in average body mass than the Eurasian species.[30] The head-and-body length of adult North American beavers is 74–90 cm (29–35 in), with the tail adding a further 20–35 cm (7.9–13.8 in). Very old individuals can exceptionally exceed normal sizes, weighing more than 40 kg (88 lb) or even as much as 50 kg (110 lb) (higher than the maximum known for the Eurasian beaver).[33][34][35][36]

    Like the capybara, the beaver is semiaquatic. The beaver has many traits suited to this lifestyle. It has a large, flat, paddle-shaped tail and large, webbed hind feet. The unwebbed front paws are smaller, with claws. The eyes are covered by a nictitating membrane which allows the beaver to see under water. The nostrils and ears are sealed while submerged. A thick layer of fat under its skin insulates the beaver from its coldwater 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 colors, but usually is dark brown. Scent glands near the genitals secrete an oily substance known as castoreum, which the beaver uses to waterproof its fur.

    Before their near-extirpation by trapping in North America, beavers were practically ubiquitous and lived from the arctic tundra to the deserts of northern Mexico, and from the Atlantic to the Pacific Oceans.[37][38][39] Physician naturalist Edgar Alexander Mearns' 1907 report of beaver on the Sonora River may be the earliest report on the southernmost range of this North American aquatic mammal.[40] However, beavers have also been reported both historically and contemporaneously in Mexico on the Colorado River, Bavispe River, and San Bernardino River in the states of Sonora and Chihuahua.[41][42][43]

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    Skull of a North American Beaver found on San Francisco Bay shore

    Behavior

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    Beaver lodge, Ontario, Canada
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    Beaver dam, northern California, USA
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    Beavers use rocks for their dams when mud and branches are less available as seen on Bear Creek, a tributary to the Truckee River, in Alpine Meadows, California.

    Beavers are active mainly at night. They are excellent swimmers and may remain submerged 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 lakes, streams, and tidal river deltas.[44] These lodges may be surrounded by water, or touching land, including burrows dug into river banks. Beavers are well known for building dams across streams and constructing their lodges in the artificial ponds which form. 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 purpose of the dam is to create deepwater refugia enabling the beaver to escape from predators. When deep water is already present in lakes, rivers, or larger streams, the beaver may dwell in a bank burrow and bank lodge with an underwater entrance. The beaver dam is constructed using branches 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.[45] The trees are cut down using their strong incisor teeth. Their front paws are used for digging and carrying and placing materials. 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 do not repair breaches in the dam made by otters, and sometimes breach the dam themselves and lower the water level in the pond 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.[46]

    Beavers are best known 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 tested 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.[47] The largest beaver dam is 2,790 ft (850 m) in length—more than half a mile long—and was discovered via satellite imagery in 2007.[48] 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 1,244 ft (379 m).[49]

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    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 also take birch, maple, willow, alder, black cherry, red oak, beech, ash, hornbeam, and occasionally pine and spruce.[50] They also eat cattails, water lilies, and other aquatic vegetation, especially in the early spring (and contrary to widespread belief,[51] 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 under water (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 up to two years.

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    Brooklyn Museum – American Beaver – John J. Audubon

    Common natural predators include coyotes, wolves, and mountain lions. Beavers can be particularly important food for lone wolves.[52] American black bears may also prey on beavers if the opportunity arises, often by smashing their paws into the beavers' lodges.[53][54][55] Perhaps due to differing habitat preferences, brown bears were not known to hunt beavers in Denali National Park.[56] Less significant predators include wolverines, which may attack a rare beaver of up to adult size, and Canadian lynx, bobcats, and foxes, predators of kits or very sick or injured animals rather than full-grown beavers due to their increasingly smaller size. American alligators, which only minimally co-exist in the wild with beavers, also seldomly threaten them. Both golden eagles (Aquila chrysaetos) and bald eagles (Haliaeetus leucocephalus) may on occasion prey on a beaver, most likely only small kits.[57] Despite repeated claims, no evidence shows that river otters are typically predators of beavers but ancedotedly may take a rare beaver kit.[58]

    Reproduction

    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.[59] Most beaver do not reproduce until they are three years of age, but about 20% of two-year-old females reproduce.[60]

    Subspecies

    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 beavers in North America are of two beaver teeth near Dayville, Oregon, and are 7 million years old.[61]

    At one time, 25 subspecies of beavers 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 substantial genetic mixing of populations has occurred 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).[62] The Canadian beaver originally inhabited almost all of the forested area of Canada,[63] 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

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    Skulls of a European and Canadian beaver.

    Although North American beavers are superficially similar to the European beaver (Castor fiber), several important differences exist 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 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 relatives, 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 glands 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 color is also different. Overall, 50% of North American beavers have pale brown fur, 25% are reddish brown, 20% are brown, and 6% are blackish, while in European beavers, 66% have pale brown or beige fur, 20% are reddish brown, nearly 8% are brown, and only 4% have blackish coats.[64]

    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.[64]

    Ecology

    The beaver was trapped out and almost extirpated in North America because its fur and castoreum were highly sought after.[38] The beaver furs were used to make clothing and beaver hats. 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.[65] From 1630 to 1640, around 80,000 beavers were taken annually from the Hudson River and western New York.[66] From 1670 onwards, the Hudson's Bay Company sent two or three trading ships into the bay every year to take furs to England from Canada. Archaeological and historical evidence suggests that beaver ponds created "moth-hole like" habitats in the deciduous forest that dominated eastern North America. This nonforest habitat attracted both Native American and early colonial hunters to the abundant fish, waterfowl, and large game attracted to the riparian clearings created by these aquatic mammals. The first colonial farmers were also attracted to the fertile, flat bottomlands created by the accumulated silt and organic matter in beaver ponds.[67]

    As eastern beaver populations were depleted, English, French, and American trappers pushed west. 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, an earlier, 19th-century California Fur Rush drove the earliest American settlement in that state. During the roughly 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; this is a fraction of the originally estimated 100 to 200 million North American beavers before the days of the fur trade.[68][69]

    These animals are considered pests in parts of their range because their dams can cause flooding, or because their habit of felling trees can pose danger to people, as in Charlotte, North Carolina's Park Road Park.[70] Because they are persistent in repairing damage to the dam, they were historically relocated or exterminated. Nonlethal methods of containing beaver-related flooding have been developed.[71] One such flow device has been used by both the Canadian and U.S. governments, called "beaver deceivers" or levelers, invented and pioneered by wildlife biologist Skip Lisle.[72]

    The beaver is a keystone species, increasing biodiversity in its territory through creation of ponds and wetlands.[73] As wetlands are formed and riparian habitats enlarged, aquatic plants colonize newly available watery habitat. Insect, invertebrate, fish, mammal, and bird diversities are also expanded.[74]

    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 beavers on openwater area in east-central Alberta, Canada, found that the mammals were associated with a 9-fold increase in openwater area. Beavers returned to the area in 1954 after a long absence since their extirpation by the fur trade in the 19th century. During drought years, where beavers were present, 60% more open water was available than those same areas during previous drought periods when beavers were absent. The authors concluded that beavers have a dramatic influence on the creation and maintenance of wetlands even during extreme drought.[75][76]

    From streams in the Maryland coastal plain to Lake Tahoe, beaver ponds have been shown to remove sediment and pollutants, including total suspended solids, total nitrogen, phosphates, carbon, and silicates, thus improving stream water quality.[77][78] 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.[79]

    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, was putatively carried by beavers. Further research has shown that many animals and birds carry this parasite, and the major source of water contamination is by humans.[80][81][82] 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.[83] New Zealand has giardia outbreaks, but no beavers, whereas Norway has plenty of beavers, but had no giardia outbreaks until recently (in a southern part of Norway densely populated by humans but no beaver).[84]

    Effects on bird abundance and diversity

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    Canada goose nest on beaver lodge

    Beavers help waterfowl by creating increased areas of water, and in northerly latitudes, they thaw areas of open water, allowing an earlier nesting season.[85] In a study of Wyoming streams and rivers, watercourses with beavers had 75-fold more ducks than those without.[86]

    Trumpeter swans (Cygnus buccinator) and Canada geese (Branta canadensis) often depend on beaver lodges as nesting sites.[74][87][88] 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.[89][90]

    Beavers may benefit birds frequenting their ponds in several additional ways. Removal of some pondside trees by beavers increases the density and height of the grass–forb–shrub layer, which enhances waterfowl nesting cover adjacent to ponds.[74] Both forest gaps where trees had been felled by beavers 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.[91] Coppicing of waterside willows and cottonwoods by beavers leads to dense shoot production which provides important cover for birds and the insects on which they feed.[92] 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 semiarid climates.[93]

    As trees are drowned by rising beaver impoundments, they become ideal nesting sites for woodpeckers, which carve cavities that attract many other bird species, including flycatchers (Empidonax spp.), tree swallows (Tachycineta bicolor), tits (Paridae spp.), wood ducks (Aix sponsa), goldeneyes (Bucephala spp.), mergansers (Mergus spp.), owls (Tytonidae, Strigidae) and American kestrels (Falco sparverius).[74] Piscivores, including herons (Ardea spp.), grebes (Podicipedidae), cormorants (Phalacrocorax ssp.), American bitterns (Botaurus lentiginosa), great egret (Ardea alba), snowy egret (Egretta thula), mergansers, and belted kingfishers (Megaceryle alcyon), use beaver ponds for fishing. Hooded mergansers (Lophodytes cucullatus), green heron (Butorides virescens), great blue heron (Ardea herodias) and belted kingfisher appeared more frequently in New York wetlands where beaver were active than at sites with no beaver activity.[94]

    By perennializing streams in arid deserts, beavers can create habitat which increases abundance and diversity of riparian-dependent species. For example, such as the upper San Pedro River in southeastern Arizona, reintroduced beavers have created willow and pool habitat which has extended the range of the endangered Southwestern willow flycatcher (Empidonax trailii extimus) with the southernmost verifiable nest recorded in 2005.[95]

    Effects on trout and salmon

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    Salmon (Oncorhynchus nerka) jumping beaver dam

    Beaver ponds have been shown to have a beneficial effect on trout and salmon populations. 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 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.[96] This study also found that beaver ponds increased smolt salmon production 80 times more than the placement of large woody debris.[96] Swales and Leving had previously shown on the 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.[97] The presence of beaver dams has also been shown to increase either 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.[98] 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.[99] Similarly, brook trout, coho salmon, and sockeye salmon (Oncorhynchus nerka) were significantly larger in beaver ponds than those in unimpounded stream sections in Colorado and Alaska.[100][101] In a recent study on a headwater Appalachian stream, brook trout were also larger in beaver ponds.[102]

    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.[103] 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.[104] 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 2 metres (6.6 ft) high.[105] Rainbow, brown, and brook trout have been shown to cross as many as 14 consecutive beaver dams.[98] Both adults and juveniles of coho salmon, steelhead trout, sea run cutthroat (Oncorhyncus clarki clarki), Dolly Varden trout (Salvelinus malma malma), and sockeye salmon are able to cross beaver dams.[103] In southeast Alaska, coho jumped dams as high as two meters, were found above all beaver dams and had their highest densities in streams with beaver.[106] In Oregon coastal streams, beaver dams are ephemeral and almost all wash out in high winter flows only to be rebuilt every summer.[107] 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.[108] Downstream migration of Atlantic salmon smolts was similarly unaffected by beaver dams, even in periods of low flows.[108] 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.[109]

    The importance of winter habitat to salmonids afforded by beaver ponds may be especially important 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."[110] Cutthroat trout and bull trout 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.[108] 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, these are generally short-lived, as the dams are overtopped, blown out, or circumvented by storm surges.[104]

    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.[111] 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.[112] 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. Research in Washington 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.[96]

    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.[44][113]

    Effects on riparian trees and vegetation

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    Tree felled by beaver (C. c. canadensis), diameter 20 cm

    Conventional wisdom has held that beavers 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 beavers 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 mountains; however willow (Salix spp.) responded by regrowing vigorously in most reaches. He further speculated that without control of beaver populations, aspen and cottonwood could go extinct on the Truckee River.[114] Not only have aspen and cottonwood survived ongoing beaver colonization, but a recent study of ten Sierra Nevada streams in the Lake Tahoe basin using aerial multispectral videography has also shown that deciduous, thick herbaceous, and thin herbaceous vegetation are more highly concentrated near beaver dams, whereas coniferous trees are decreased.[115] These findings are consistent with those of Pollock, who reported that in Bridge Creek, a stream in semiarid 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.[116] In a second study of riparian vegetation based on observations of Bridge Creek over a 17-year 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 resprout after beaver cutting, they frequently grew from seeds landing on freshly exposed alluvial deposits subsequent to beaver activity.[117] 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 is 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 beyond the stream banks to wide riparian zones when beaver dams are present.

    Finally, beaver ponds may serve as critical firebreaks in fire-prone areas.[118]

    Beavers and stream restoration

    In the 1930s, the U.S. government put 600 beavers to work alongside the Civilian Conservation Corps in projects to stop soil erosion by streams in Oregon, Washington, Wyoming, and Utah. At the time, each beaver, whose initial cost was about $5, completed work worth an estimated $300.[119] In 2014, a review of beaver dams as stream restoration tools proposed that an ecosystem approach using riparian plants and beaver dams could accelerate repair of incised, degraded streams versus physical manipulation of streams.[120]

    The province of Alberta published a booklet providing information on using beaver for stream restoration.[121]

    Utah published a Beaver Management Plan which includes reestablishing beavers in ten streams per year for the purpose of watershed restoration each year from 2010 through 2020.[122]

    In a pilot study in Washington, the Lands Council is reintroducing beavers to the upper Methow River Valley in the eastern Cascades to evaluate its 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 autumn season.[123] Beavers were nearly exterminated in the Methow watershed by the early 1900s by fur trappers. This project was developed in response to a 2003 Washington Department of Ecology proposal to spend as much as $10 billion on construction of several dams on Columbia River tributaries to retain storm-season runoff.[124] As of January, 2016, 240 beavers released into the upper Methow River at 51 sites had built 176 beaver ponds, storing millions of gallons of water in this semiarid east region.[125] One beaver that was passive integrated transponder tagged and released in the upper part of the Methow Valley, swam to the mouth of the Methow River, then up the Okanogan River almost to the Canada–US border, a journey of 120 miles (190 km).[126][127]

    Urban beavers

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    Beaver before being drowned by trapper's snare in Lincoln Park, Chicago 2008
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    After trapping, beaver lodge reappears in Lincoln Park, Chicago, fall, 2009

    After 200 years, a lone beaver returned to New York City in 2007, making its home along the Bronx River, having spent time living at the Bronx Zoo and the Botanical Gardens.[128] Though beaver pelts were once important to the city's economy and a pair of beavers appears on the city's official seal and flag, beavers had not lived in New York City since the early 19th century, when trappers extirpated them completely from the city.[129] The return of "José", named after Representative José Serrano from the Bronx, has been seen as evidence that efforts to restore the river have been successful.[130][131][132] In the summer of 2010, a second beaver named "Justin" joined José, doubling the beaver population in New York City.[133] In February 2013, what appears to be both José and Justin were caught on motion-sensitive cameras at the New York Botanical Garden.[134]

    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.[135] 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 beaver recolonizing North Pond in Lincoln Park has been recorded in 1994, 2003, 2004, 2008, 2009, 2014, and 2018[135][136][137][138] 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.[139] 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".[140] 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 beavers have transformed Alhambra Creek from a trickle into multiple dams and beaver ponds, which in turn, led to the return of steelhead trout and river otter in 2008, and mink in 2009.[141][142] The Martinez beavers probably originated from the Sacramento-San Joaquin River Delta, which once held the largest concentration of beavers in North America.[143]

    In 1999, Washington, DC's annual Cherry Blossom Festival was interrupted by a family of beavers that 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.[144][145]

    As introduced non-native species

     src=
    Beaver damage on the north shore of Robalo Lake, Navarino Island, Chile

    In the 1940s, beavers were brought to Tierra del Fuego in southern Chile and Argentina for commercial fur production and introduced near 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 main island, and to other islands in the archipelago, 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.[146] Although the dominant Lenga beech (Nothofagus pumilio) forest can regenerate from stumps, most of the newly created beaver wetlands are being colonized by the rarer native 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.[146] In contrast, areas with introduced beaver were associated with increased populations of the native catadromous puye fish (Galaxias maculatus).[147][148] 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.[148] They have also been found to cross saltwater to islands northward; and reached the Chilean mainland in the 1990s.[149] 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.[150]

    North American beavers were also released in Finland in 1937, before it was realized that they formed a separate species. (Eurasian beavers had been extirpated from the region, so the release was intended as a reintroduction project.) By 1999, it was estimated that 90% of beavers in Finland were the American species. The species is not considered invasive, as in Europe it has a similar keystone effect to European beavers, which have not recolonized the area. The beaver population has been controlled by issuing hunting licenses.[151] A report in 2010 concluded that while the current population was not problematic, as the species has larger litters than European beavers and builds somewhat larger dams, it could become a problem if its range continues expanding into Russia, but this does not seem to be taking place.[152]

    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 Native Americans.[citation needed] Early French Canadian Catholics considered beaver to be "four-legged fish" that could be eaten at Lent.[153]

    Despite their name, the fried pastries found in parts of Canada called BeaverTails contain no beaver. Their name derives from its wide, flat shape, which resembles a beaver's tail.

    Symbolism

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    Beaver sculpture over entrance to Canadian Parliament Building

    As one of the national sovereignty animal symbols of Canada,[154] the North American beaver is depicted on the Canadian nickel.[154] This beaver was also featured on the first Canadian postage stamp, the Three Penny Beaver, which is considered the first postage stamp to show an animal instead of a head of state.[155] It is also the state animal of Oregon and New York of the United States, 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 coats of arms of the Hudson's Bay Company,[156] 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 Albany, New York and New York City included the beaver.

    See also

    References

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    117. ^ Demmer, Rick & Beschta, Robert L. (September 2008). "Recent History (1988–2004) of Beaver Dams along Bridge Creek in Central Oregon". Northwest Science. 82 (4): 309–318. doi:10.3955/0029-344X-82.4.309.
    118. ^ Collier, Eric (1959). Three Against the Wilderness. Victoria, British Columbia: Touchwood. p. 288. ISBN 1-894898-54-0.
    119. ^ Ruedemann, Rudolf & Schoonmaker, W. J. (December 2, 1938). "Beaver-Dams as Geologic Agents". Science. 88 (2292): 523–525. Bibcode:1938Sci....88..523R. doi:10.1126/science.88.2292.523. PMID 17840531.
    120. ^ Michael M. Pollock; Timothy J. Beechie; Joseph M. Wheaton; Chris E. Jordan; Nick Bouwes; Nicholas Weber & Carol Volk (April 4, 2014). "Using Beaver Dams to Restore Incised Stream Ecosystems". BioScience. 64 (4): 279–290. doi:10.1093/biosci/biu036. Retrieved March 12, 2016.
    121. ^ Fitch, L. (2016). Caring for the Green Zone: Beaver - Our Watershed Partner (PDF). Lethbridge, Alberta: Cows and Fish - Alberta Riparian Habitat Management Society. ISBN 978-0-9688541-6-7. Retrieved March 12, 2016.
    122. ^ Utah Beaver Management Plan (PDF) (Report). Utah Division of Wildlife Resources. January 6, 2010. p. 25. Retrieved August 29, 2010.
    123. ^ Groc, Isabelle (April 19, 2010). "Beavers Sign up to Fight Effects of Climate Change". Discover. Retrieved July 27, 2010.
    124. ^ "The Beaver Solution: Solving our Water Storage Dilemma in Eastern Washington". The Lands Council. March 2010. Archived from the original on July 4, 2009. Retrieved July 27, 2010.
    125. ^ "Beavers may be part of answer to climate change". Methow Valley News. January 23, 2016. Retrieved March 12, 2016.
    126. ^ Ann McCreary (January 24, 2016). "Beavers may be part of answer to climate change". Methow Valley News. Retrieved March 12, 2016.
    127. ^ Ben Goldfarb (Nov 9, 2015). "The beaver whisperer". High Country News. Retrieved March 12, 2016.
    128. ^ "New York City Beaver Returns". Science Daily. December 20, 2008.
    129. ^ Miller, Peter (September 2009). "Manhattan Before New York: When Henry Hudson first looked on Manhattan in 1609, what did he see?". National Geographic.
    130. ^ O'Connor, Anahad (February 23, 2007). "After 200 Years, a Beaver Is Back in New York City". The New York Times. Retrieved Dec 4, 2009.
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    156. ^ The HBC Coat of Arms, Hbc Heritage

Distribution

    Distribution
    provided by Fire Effects Information System Animals
    More info for the term: tundra

    The American beaver is found throughout most of North America except in the
    Arctic tundra, peninsular Florida, and the Southwestern deserts
    [2,31,35]. The distribution of six subspecies is listed below [10,19].
    The distribution of the other seven was not found in the literature.

    C. c. subsp. carolinensis - occurs in the southeastern part of the United
    States north to southern Virginia, northern Ohio, Indiana, Illinois, and
    west to southeastern Iowa, eastern Missouri, eastern Arkansas and
    Louisiana [19].

    C. c. subsp. taylori - occurs in northern Nevada in the streams and
    tributaries of the Snake River drainage [10].

    C. c. subsp. baileyi - occurs in the Humboldt River drainage [10].

    C. c. subsp. repentinus - occurs along the Colorado River [10].

    C. c. subsp. texensis - occurs in eastern Texas [10].

    C. c. subsp. leucodenta - occurs along the Coast Ranges from California to
    Alaska [10].
    Occurrence in North America
    provided by Fire Effects Information System Animals

    AL
    AK
    AZ
    AR
    CA
    CO
    CT
    DE
    FL
    GA

    ID
    IL
    IN
    IA
    KS
    KY
    LA
    ME
    MD

    MA
    MI
    MN
    MS
    MO
    MT
    NE
    NV
    NH
    NJ

    NM
    NY
    NC
    ND
    OH
    OK
    OR
    PA
    RI
    SC

    SD
    TN
    TX
    UT
    VT
    VA
    WA
    WV
    WI
    WY

    DC
    PR
    VI

    AB
    BC
    MB
    NB
    NF
    NT
    NS
    ON
    PE
    PQ

    SK
    YT


    MEXICO


    Regional Distribution in the Western United States
    provided by Fire Effects Information System Animals
    More info on this topic.

    This species can be found in the following regions of the western United States (according to the Bureau of Land Management classification of Physiographic Regions of the western United States):

    1 Northern Pacific Border
    2 Cascade Mountains
    3 Southern Pacific Border
    4 Sierra Mountains
    5 Columbia Plateau
    6 Upper Basin and Range
    7 Lower Basin and Range
    8 Northern Rocky Mountains
    9 Middle Rocky Mountains
    10 Wyoming Basin
    11 Southern Rocky Mountains
    12 Colorado Plateau
    13 Rocky Mountain Piedmont
    14 Great Plains
    15 Black Hills Uplift
    16 Upper Missouri Basin and Broken Lands
    Distribution
    provided by Animal Diversity Web

    Beavers are found throughout all of North America except for the northern regions of Canada and the deserts of the southern United States and Mexico.

    Biogeographic Regions: nearctic (Native )

Morphology

    Morphology
    provided by Animal Diversity Web

    Beavers are primarily aquatic animals, and the largest rodents in North America. They have a waterproof, rich, glossy, reddish brown or blackish brown coat. The underhairs are much finer than the outer, protective, guard-hairs. The ears are short, round, and dark brown in coloration. A beaver's hind legs are longer than its front legs, thus making the rear end to be higher than the front end while walking.

    Beaver skulls and teeth are disproportionately large. This is crucial for cutting through hard woods like maple and oak. Most noteably, the upper incisors, bright orange in color, are at least 5 mm wide and 20-25 mm long. These teeth grow throughout the animal's lifetime and are a necessity to survival, just as the animal's closable nostrils, closable ears, and transparent eye membranes are for aquatic existence.

    Also notable are the anal and castor glands, found in both male and female beavers. Both sets of glands lie at the base of the tail, which is possibly the most defining characteristic of the beaver. It is broad, flat, and covered in large blackish scales. The anal and castor glands have been recorded as large as 3.4 by 2.2 inches for the castors, and 3.0 by 1 inch for the anal glands. Secretions from these glands are used in scent-marking, and give the beaver its odd odor.

    Beavers also have anal and castor glands, which they use to mark their territory. These glands are located beneath the tail. A beaver's tail is broad, flat, and covered with large black scales.

    Range mass: 13 to 32 kg.

    Range length: 900 to 1170 mm.

    Sexual Dimorphism: sexes alike

    Other Physical Features: endothermic ; bilateral symmetry

Habitat

    Associated Plant Communities
    provided by Fire Effects Information System Animals
    American beavers commonly inhabit riparian areas of mixed coniferous-deciduous
    forests and deciduous forests containing abundant American beaver foods and lodge
    building material such as quaking aspen (Populus tremuloides), willows
    (Salix spp.), alders (Alnus spp.), red-osier dogwood (Cornus sericea),
    and cottonwoods (Populus spp.) [2,25].
    Cover Requirements
    provided by Fire Effects Information System Animals
    More info for the term: cover

    The lodge is the major source of escape, resting, thermal, and
    reproductive cover for American beavers. Lodges may be surrounded by water or
    constructed against a bank. Water protects the lodge from predators and
    provides concealment for American beavers when traveling to and from food
    gathering areas and caches [2]. On lakes and ponds, lodges are
    frequently situated in areas that provide shelter from wind, waves, and
    ice [2]. Damming large streams with swift, turbulent waters creates
    calm pools for feeding and resting [11].
    Habitat: Cover Types
    provided by Fire Effects Information System Animals
    More info on this topic.

    This species is known to occur in association with the following cover types (as classified by the Society of American Foresters):

    16 Aspen
    18 Paper birch
    19 Gray birch - red maple
    20 White pine - northern red oak - red maple
    22 White pine - hemlock
    24 Hemlock - yellow birch
    25 Sugar maple - beech - yellow birch
    26 Sugar maple - basswood
    27 Sugar maple
    28 Black cherry - maple
    30 Red spruce - yellow birch
    31 Red spruce - sugar maple - beech
    35 Paper birch - red spruce - balsam fir
    39 Black ash - American elm - red maple
    57 Yellow-poplar
    58 Yellow-poplar - eastern hemlock
    59 Yellow-poplar - white oak - northern red oak
    60 Beech - sugar maple
    61 River birch - sycamore
    62 Silver maple - American elm
    63 Cottonwood
    88 Willow oak - water oak - diamondleaf oak
    93 Sugarberry - American elm - green ash
    95 Black willow
    96 Overcup oak - water hickory
    108 Red maple
    202 White spruce - paper birch
    203 Balsam poplar
    210 Interior Douglas-fir
    212 Western larch
    213 Grand fir
    217 Aspen
    221 Red alder
    222 Black cottonwood - willow
    229 Pacific Douglas-fir
    230 Douglas-fir - western hemlock
    235 Cottonwood - willow
    243 Sierra Nevada mixed conifer
    244 Pacific ponderosa pine - Douglas-fir
    245 Pacific ponderosa pine
    251 White spruce - aspen
    252 Paper birch
    254 Black spruce - paper birch
    Habitat: Ecosystem
    provided by Fire Effects Information System Animals
    More info on this topic.

    This species is known to occur in the following ecosystem types (as named by the U.S. Forest Service in their Forest and Range Ecosystem [FRES] Type classification):

    FRES11 Spruce-fir
    FRES12 Longleaf-slash pine
    FRES13 Loblolly-shortleaf pine
    FRES14 Oak-pine
    FRES15 Oak-hickory
    FRES16 Oak-gum-cypress
    FRES17 Elm-ash-cottonwood
    FRES18 Maple-beech-birch
    FRES19 Aspen-birch
    FRES20 Douglas-fir
    FRES21 Ponderosa pine
    FRES22 Western white pine
    FRES23 Fir-spruce
    FRES25 Larch
    FRES28 Western hardwoods
    Habitat: Plant Associations
    provided by Fire Effects Information System Animals
    More info on this topic.

    This species is known to occur in association with the following plant community types (as classified by Küchler 1964):

    More info for the terms: bog, forest

    K005 Mixed conifer forest
    K011 Western ponderosa forest
    K014 Grand fir - Douglas-fir forest
    K016 Eastern ponderosa forest
    K017 Black Hills pine forest
    K018 Pine - Douglas-fir forest
    K020 Spruce - fir - Douglas-fir forest
    K021 Southwestern spruce - fir forest
    K025 Alder - ash forest
    K029 California mixed evergreen forest
    K093 Great Lakes spruce - fir forest
    K094 Conifer bog
    K095 Great Lakes pine forest
    K096 Northeastern spruce - fir forest
    K098 Northern floodplain forest
    K099 Maple - basswood forest
    K100 Oak - hickory forest
    K101 Elm - ash forest
    K102 Beech - maple forest
    K103 Mixed mesophytic forest
    K106 Northern hardwoods
    K107 Northern hardwoods - fir forest
    K109 Transition between K104 and K106
    K110 Northeastern oak - pine forest
    K111 Oak - hickory - pine forest
    K112 Southern mixed forest
    K113 Southern floodplain forest
    Preferred Habitat
    provided by Fire Effects Information System Animals
    Suitable habitat for American beavers must contain all of the following: stable
    aquatic habitat providing adequate water; channel gradient of less than
    15 percent; and quality food species present in sufficient quantity [2].
    American beavers can usually control water depth and stability on small streams,
    ponds, and lakes. Large lakes or reservoirs (20 acres [8 ha] in surface
    area) with irregular shorelines provide optimum habitat for the species.
    Lakes and reservoirs that have extreme annual or seasonal fluctuations
    in the water level are generally unsuitable habitat for American beavers [2,28].
    Intermittent streams or streams that have major fluctuations in
    discharge will have little year-round value as American beaver habitat [2].

    Stream characteristics such as gradient, depth, and width are
    determining factors in habitat use by American beaver [2,11]. Steep topography
    prevents the establishment of a food transportation system [2].
    Additionally, narrow valley bottoms cannot support the large amounts of
    vegetation needed by American beavers. Consequently American beaver populations in narrow
    valley bottoms are more cyclic than are populations in wider valley
    bottoms [24]. Valleys less than 150 feet (46 m) wide are occupied less
    frequently [2,24]. One study found that 68 percent of the American beaver
    colonies recorded in Colorado were in valleys with a stream gradient of
    less than 6 percent. No American beaver colonies were recorded in streams with a
    gradient of 15 percent or more. Valleys that were only as wide as the
    stream channel were unsuitable American beaver habitat, while valleys wider than
    the stream channel were frequently occupied by American beavers [24].

    Food availability is another factor determining suitable habitat for
    American beavers [11]. Marshes, ponds, and lakes are often occupied by American beavers
    when an adequate supply of food is available. American beavers generally forage
    no more than about 300 feet (90 m) from water; however, foraging
    distances of up to 656 feet (200 m) have been reported [2].
    Habitat
    provided by Animal Diversity Web

    Beavers live in lodges, of which there are three types: those built on islands, those built on the banks of ponds, and those built on the shores of lakes. The island lodge consists of a central chamber, with its floor slightly above the water level, and with two entrances. One entrance opens up into the center of the hut floor, while the other is a more abrupt descent into the water.

    The lodge, itself, is an oven-shaped house of sticks, grass, and moss, woven together and plastered with mud. Over the years, repair and elaboration leads to an increase in hut size. The room inside may measure 2.4 m (8 ft) wide and up to 1 m (3 ft) high. The floor is blanketed with bark, grass, and wood chips.

    The pond lodge is built either a short way back from the edge of the bank, or partly hanging over it, with the front wall built up from the bottom of the pond. The lake lodge is built on the shelving shores of lakes. To ensure adequate water depth surrounding the lodge, beavers dam streams with logs, branches, mud, and stones.

    Habitat Regions: temperate ; terrestrial ; freshwater

    Terrestrial Biomes: forest

    Aquatic Biomes: lakes and ponds; rivers and streams

Trophic Strategy

    Food Habits
    provided by Fire Effects Information System Animals
    More info for the terms: fresh, herbaceous, shrubs, tree

    American beavers are herbivores. During late spring and summer their diet
    consists mainly of fresh herbaceous matter [2,18]. American beavers appear to
    prefer herbaceous vegetation over woody vegetation during all seasons if
    it is available. Woody vegetation may be consumed during any season,
    although its highest utilization occurs from late fall through early
    spring when herbaceous vegetation is not available. The majority of the
    branches and stems of woody vegetation are cached for later use during
    the winter [2].

    Winter is a critical period, especially for colonies on streams because
    they must subsist solely on their winter food caches. In contrast with
    stream American beavers, colonies on lakes are not solely dependent on their
    stores of woody vegetation; they can augment their winter diet of bark
    with aquatic plants [18].

    Aquatic vegetation such as duck-potato (Sagittaria spp.), duckweed
    (Lemma spp.), pondweed (Potamogeton spp.), and water weed (Elodea spp.)
    are preferred foods when available [2]. The thick, fleshy rhizomes of
    water lilies (Nymphaea spp. and Nuphar spp.) may be used as a food
    source throughout the year. If present in sufficient amounts, water
    lily rhizomes may provide an adequate winter food source, resulting in
    little or no tree cutting or food caching of woody materials [2,18].
    Other important winter foods of American beavers living on lakes include the
    rhizomes of sedges and the rootstocks of mat-forming shrubs [18].

    Important woody foods of American beavers include quaking aspen, willow,
    cottonwood, alder, red maple (Acer rubrum), serviceberry (Amelanchier
    spp.), mountain maple (Acer glabrum), red-osier dogwood, and green ash
    (Fraxinus pennsylvanica) [2,18,22]. Other woody species occasionally
    utilized for food include sugar maple (Acer saccharum), black ash
    (Fraxinus nigra), yellow birch (Betula alleghaniensis), hazels (Corylus
    spp.), hemlocks (Tsuga spp.), and Oregon crab apple (Malus fusca)
    [18,21]. Aspen and willows are considered preferred American beaver foods;
    however, these are generally riparian tree species and may be more
    available for American beaver foraging but not necessarily preferred over all
    other deciduous tree species. American beavers have been reported to subsist in
    some areas by feeding on conifer trees; however, these trees are a poor
    quality source of food [2].

    Woody stems cut by American beavers are usually less than 3 to 4 inches (7.6-10.1
    cm) in d.b.h. One study reported that trees of all size classes were
    felled close to the water's edge, while only smaller diameter trees were
    felled farther from the shore. Trees and shrubs closest to the water's
    edge are generally utilized first [2].
    Trophic Strategy
    provided by Animal Diversity Web

    Beavers eat bark and cambium (the softer growing tissue under the bark of trees). Their favorites include willow, maple, poplar, beech, birch, alder, and aspen trees. They also eat water vegetation, as well as buds, and roots. Cellulose, which usually can not be digested by mammals, is a major component of their diet. Beavers have microorganisms in their cecum (a sac between the large and small intestine) that digest this material. In zoos, beavers are fed yams, lettuce, carrots and "rodent chow."

    Plant Foods: leaves; roots and tubers; wood, bark, or stems

    Primary Diet: herbivore (Lignivore)

Associations

    Predators
    provided by Fire Effects Information System Animals
    More info for the term: natural

    American beavers have few natural predators. However, in certain areas, American beavers
    may face predation pressure from wolves (Canis lupus), coyotes (Canis
    latrans), lynx (Lynx canadensis), fishers (Martes pennanti), wolverines (Gulo
    gulo), and occasionally bears (Ursus spp.). Alligators, minks (Mustela
    vison), otters (Lutra canadensis), hawks, and owls periodically prey on
    kits [19,22,27]. Humans kill American beavers for their fur [18,22].
    Associations
    provided by Animal Diversity Web

    Beavers maintain wetlands that can slow the flow of floodwaters. They prevent erosion, and they raise the water table, which acts as a purifying system for the water. This happens because silt occurs upstream from dams, and toxins are then broken down. As ponds grow from water backed up by the damn, pond weeds and lilies take over. After beavers leave their homes, the dams decay, and meadows appears.

    Ecosystem Impact: creates habitat; keystone species

    Associations
    provided by Animal Diversity Web

    Young beavers are very vulnerable, and are threatened by bears, wolves, wolverines, lynx, fishers and otters. An adult beaver's size is a deterrent to most predators, and though natural predators pose a very real danger to kits, man has proven to be, by far, the most dangerous predator to beavers. Killing beavers for their pelts, disrupting them through a change in habitat, and slowly poisoning them through pollution, which is known to infect wounds, all have lead to the threat which man poses on beavers.

    Known Predators:

    • wolves (Canis lupus)
    • wolverines (Gulo gulo)
    • lynx (Lynx canadensis)
    • northern river otters (Lontra canadensis)
    • humans (Homo sapiens)
    • black bears and brown bears (Ursus)
    • fishers (Martes pennanti)

General Ecology

    Habitat-related Fire Effects
    provided by Fire Effects Information System Animals
    More info for the terms: climax, forest, succession

    Fire occurring in riparian areas often benefits American beaver populations [16].
    American beavers are adapted to the early stages of forest succession. Quaking
    aspen, willows, alders, and red-osier dogwood, prime American beaver food trees,
    all sprout vigorously after fire. As succession progresses, these trees
    become too large for American beavers to use or are replaced by climax trees
    [34]. Recurring fires within parts of boreal forests have allowed aspen
    and willow to replace coniferous forests. This change favors American beaver
    populations, since both species are important food sources. Fire may
    also help create more open bodies of water [16].
    Timing of Major Life History Events
    provided by Fire Effects Information System Animals
    More info for the term: litter

    Breeding season - Breeding occurs between January and March
    [18,30,31,35]. American beavers are generally monogamous, although males will
    mate with other females [22,31]. Only the colony's dominant female
    breeds, producing one litter a year [30].

    Gestation/litter - Gestation period lasts 4 months. Average litter size
    varies between 2.3 and 4.1 [27,30,31,35]. Kits are weaned at 2 to 3
    months and can swim by 1 week of age [31,35].

    Age at sexual maturity - American beavers become sexually mature between age 2
    and 3 [18,36].

    Colony/dispersal - The colony consists of three age classes of American beavers:
    the adults, the kits, and the yearlings born the previous spring
    (average 5.1 American beavers per colony) [18]. After young American beavers reach their
    second or third year, they are forced to leave the family group
    [18,22,35]. Dispersal may be delayed in areas with high American beaver
    densities. Subadults generally leave the natal colony in the late
    winter or early spring [30]. Subadult American beavers have been reported to
    migrate as far as 147 miles (236 km), although average migration
    distances range from 5 to 10 miles (8-16 km) [2].

    Life span - Up to 11 years in the wild, 15 to 21 years in
    captivity [22,27].

    The species is active throughout the year and is usually nocturnal.
    Adult American beavers are nonmigratory [2].

Behavior

    Behavior
    provided by Animal Diversity Web

    Beavers have a pair of anal scent glands, called castors, which secrete a musk-like substance called castoreum. This is used mainly for marking territories. The broad, flat, scaly tail is about 25 cm (about 10 in) long and serves as a warning signal when slapped against the water. Beavers also call out to others, making a low, groaning sound.

    Communication Channels: visual ; acoustic ; chemical

    Other Communication Modes: scent marks

    Perception Channels: visual ; tactile ; acoustic ; chemical

Life Expectancy

    Lifespan, longevity, and ageing
    provided by AnAge articles
    Maximum longevity: 23.4 years (captivity) Observations: It has been suggested that beavers may live as much as 50 years (Ronald Nowak 1999), which is doubtful. One captive specimen was still alive after 23.4 years (Richard Weigl 2005).
    Life Expectancy
    provided by Animal Diversity Web

    Under favorable conditions, beavers will produce their first litters at two or three years of age. The average lifespan of a beaver in the wild is 10 to 20 years. While its size saves it from most predators, a beaver's lifespan can be cut short by predators, most commonly humans, wolves, and coyotes. Parasites and disease also play a factor in mortality.

    Typical lifespan
    Status: wild:
    10 to 20 years.

Reproduction

    Reproduction
    provided by Animal Diversity Web

    Beavers are monogamous, but if one mate dies, the other will "remarry", or seek out a new mate. Beavers are driven away from their colonies usually around their second year of life, right before a new litter is born. They then make a colony of their own, usually several kilometers away, and they first breed around their third years of life, give or take a year depending on the quality of the environmtnt.

    Mating System: monogamous

    Male and female beavers are sexually mature at about 3 years of age. They mate between January and March in cold climates, and in late November or December in the south. Beavers give birth to one litter of kits per year, usually between April and June. The gestation period is about 3 months, or 105-107 days. During this time, the young develop inside the female's body. When they are born they are fully furred,have open eyes, and can swim within 24 hours. After several days they are also able to dive out of the lodge with their parents to explore the surrounding area.

    Female beavers are sexually mature when they are about 3 years old. They give birth to one litter each year, usually between April and July. Baby beavers develop inside their mother for about 3 months. Baby beavers are called kits. When they are born they already have all of the fur and have their eyes open.

    At birth kits are usually around 38 cm long including their tales. They tend to weigh from 250 to 600 grams and can be red, brown, or almost black. They remain in the lodge for a month, afterwards leaving for longer periods of time to swim and take in solid foods. Most beavers are weaned within two weeks, although it can take up to 90 days. The young usually stay with their parents for 2 years and then leave to make their own homes.

    Breeding interval: Beavers breed once a year.

    Breeding season: Mating takes place during the winter season, usually in January or February.

    Range number of offspring: 1 to 4.

    Average gestation period: 3 months.

    Average weaning age: 2 weeks.

    Average time to independence: 2 years.

    Average age at sexual or reproductive maturity (female): 3 years.

    Average age at sexual or reproductive maturity (male): 3 years.

    Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous

    Average birth mass: 430 g.

    Average gestation period: 128 days.

    Average number of offspring: 3.5.

    Average age at sexual or reproductive maturity (male)
    Sex: male:
    639 days.

    Average age at sexual or reproductive maturity (female)
    Sex: female:
    639 days.

    Parental care begins before birth, and continues for 1-2 years until the young have reached the stage of independence. In preparation for birth females will prepare a soft bed within the lodge. She then will use her flat tail as a sort of birthing mat. She will lick each kit clean, and nurse it. Both mother and father beaver play a part in providing food for the young and protecting them from predators.

    Parental Investment: pre-hatching/birth (Provisioning: Male, Female, Protecting: Male, Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female); pre-independence (Provisioning: Male, Female, Protecting: Male, Female)

Conservation Status

    Conservation Status
    provided by Animal Diversity Web

    The conservation status differs with respect to source, but there have been significant threats to the survival of the beaver. Beavers have been hunted and trapped extensively in the past and by about 1900, the animals were almost gone in many of their original habitats. Pollution and habitat loss have also affected the survival of the beaver. In the last century, however, beavers have been successfully reintroduced to many of their former habitats.

    US Federal List: no special status

    CITES: no special status

    State of Michigan List: no special status

    IUCN Red List of Threatened Species: least concern

Management

    Management Considerations
    provided by Fire Effects Information System Animals
    More info for the terms: cover, density, forest, natural, shrubs, succession, tree

    American beavers will live in close proximity to humans if all habitat
    requirements are met [27]. However, railways, roads, and land clearing
    adjacent to waterways may affect American beaver habitat suitability. Transplants
    of American beaver may be successful on strip mined land or in new impoundments
    where water conditions are relatively stable. Highly acidic waters,
    which often occur in strip-mined areas, are acceptable for American beaver if
    suitable foods are present [2].

    American beaver activity can have a significant influence on stream and riparian
    habitats [3,14,24,30]. American beavers are the only mammals in North America
    other than humans that can fell mature trees; therefore, their ability
    to decrease forest biomass is much greater than that of other herbivores
    [2]. Additionally, American beaver ponds conserve spring runoff, thus ensuring
    more constant stream flow, diminishing floods, conserving soil, and
    helping maintain the water table [12].

    Through tree harvesting activity, American beavers can have an effect on natural
    succession. According to Barnes and Dibble [3] tree cutting by American beavers
    on the lower Chippewa River in west-central Wisconsin will alter the
    course of succession on the riverbottom site studied. American beavers were
    selective in their choice of woody plants, preferring ash (Fraxinus
    spp.) and hickory (Carya spp.) over all other woody plants. These
    authors predict a major reduction in density for future populations of
    ash, hickory, and hackberry (Celtis spp.) in areas of American beaver activity
    and an increase in the density of basswood (Tilia spp.) and elm (Ulmus
    spp.) [3].

    American beaver activity can be beneficial to some wildlife species [13,30].
    Waterfowl often benefit from the increased edge, diversity, and
    invertebrate communities created by American beaver activity [30]. Occupied
    American beaver-influenced sites produce more waterfowl because of improved water
    stability and increased brood-rearing cover; the production declines
    with American beaver abandonment. Great-blue herons (Ardea herodias), ospreys
    (Pandion halietus), bald eagles (Haliaeetus leucocephalus), kingfishers
    (Ceryle alcyon), and many species of songbirds benefit from American beaver
    activity as well. Otters, raccoons (Procyon lotor), mink, and muskrat
    (Ondatra zibithica) thrive on the increased foraging areas produced by
    American beaver activity. Berry-producing shrubs and brush in areas cut over by
    American beavers attract white-tailed deer (Odocoileus virginianus) and black
    bear (Ursus americanus) [30].

    American beaver activity can also improve fish habitat. Production of three
    trout species (Salomo spp. and Salvelines fontinalis) in a stream in the
    Sierra Nevada increased due to a higher standing crop of invertebrates
    in American beaver ponds [8]. Smallmouth bass (Micropterus dolomieuis) and
    northern pike (Esok lucius) also benefit from American beaver impoundments [30].
    In some instances American beaver ponds have provided up to six times the total
    weight of salmonids per acre than that in adjacent stream habitat
    without American beaver ponds [24]. In areas of marginal trout habitat, however,
    American beaver activity can reduce trout production. American beaver-caused loss of
    streamside shade and diminished water velocity can result in lethal
    water temperatures [30].

    The amount of influence that cattle have on riparian environment can be
    reduced by American beaver activity in many valley bottoms. If American beavers are
    thoroughly established in wide valley willow habitats prior to the
    introduction of cattle, the immediate effect of cattle on the stream is
    often minor [24].

    American beaver activity can also have detrimental effects. American beaver-caused
    flooding often kills valuable lowland timber [30]. Human/American beaver
    conflicts occur when American beavers flood roadways and agricultural lands, and
    dam culverts and irrigation systems. The economic cost of nuisance
    American beaver activities often exceeds the value of their pelts and has been
    estimated at $75 to $100 million annually in the United States.
    Additionally, American beavers have potential to increase water-borne pathogens
    (including Giardia lamblia) downstream from their activity [30].

    American beavers are harvested for their pelts. In most states with substantial
    American beaver populations, the species is now managed to provide a reliable
    annual harvest and a relatively stable population [12].
    Use of Fire in Population Management
    provided by Fire Effects Information System Animals
    More info for the terms: fire regime, forest

    Fire can be used to maintain American beaver habitat in a subclimax state, thus
    ensuring adequate food supply for American beavers [16,26,34]. High American beaver
    populations in many areas are the direct result of the extensive
    clearcutting and forest fires which were characteristic of the northern
    forests until recent years [25,34].

    FIRE REGIMES :
    Find fire regime information for the plant communities in which this
    species may occur by entering the species name in the FEIS home page under
    "Find FIRE REGIMES".

Benefits

    Benefits
    provided by Animal Diversity Web

    Although beavers are beneficial to the environment, they can destroy it also. Dams slow the flow of water in fast streams, changing the flora and fauna and sometimes creating silting. They may flood low-lying areas, sometimes causing extensive loss of timber.

    Benefits
    provided by Animal Diversity Web

    Beaver fur has been a significant trade item for the last century, creating large amounts of money for merchants.

    Beavers are incredibly beneficial to the environment. They are instrumental in creating habitats for many aquatic organisms, maintaining the water table at an appropriate level and controlling flooding and erosion, all by building dams. See the Sevilleta Long-Term Eocological Research Project (LTER)/ RKM and KVP-- University of New Mexico account on the web at http://sevilleta.unm.edu/animal/mammal/beaver.html for a more detailed explanation of the benefits of beavers in the environment.

    Positive Impacts: body parts are source of valuable material

Taxonomy

    Common Names
    provided by Fire Effects Information System Animals
    American beaver
    Canadian beaver
    beaver
    flat-tail
    bank beaver
    castor
    castor cat
    Taxonomy
    provided by Fire Effects Information System Animals
    The currently accepted scientific name for the American beaver is Castor
    canadensis Kuhl [6,10,19,22,33]. The subspecies differ in size,
    proportion, color, and skull characteristics [10,33]. The following
    subspecies have been mentioned in the literature [10,19,22,29,33]:

    C. canadensis subsp. baileyi Nelson
    C. canadensis subsp. belugae Taylor (Cook Inlet beaver)
    C. canadensis subsp. canadensis Kuhl (Canadian beaver)
    C. canadensis subsp. carolinensis Rhoads (Carolina beaver)
    C. canadensis subsp. frondator Mearns (Sonora beaver)
    C. canadensis subsp. leucodonta Gray (Pacific beaver)
    C. canadensis subsp. mexicanus Bailey (Rio Grande beaver)
    C. canadensis subsp. michiganensis Bailey (woods beaver)
    C. canadensis subsp. pacificus Rhoads (Washington beaver)
    C. canadensis subsp. phaeus Heller ( Admiralty beaver)
    C. canadensis subsp. repentinus Goldman
    C. canadensis subsp. taylori Davis
    C. canadensis subsp. texensis Bailey (Texas beaver)

Other Articles

    Untitled
    provided by Animal Diversity Web

    One of the earliest accounts of beaver natural history was written by Samuel Hearne in the late 1700s. His journal entry on beavers is online at: http://web.idirect.com/~hland/sh/an020.htm.