American beaver: Wikis


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Castor canadensis
Beaver Yearling Grooming - Alhambra Creek, Martinez, California
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Castoridae
Genus: Castor
Species: C. canadensis
Binomial name
Castor canadensis
Kuhl, 1820
Subspecies[2][3][4][5]
  • C. c. acadicus Bailey
  • C. c. baileyi Nelson
  • C. c. belugae Taylor
    Cook Inlet beaver
  • C. c. caecator Bangs
    Newfoundland beaver
  • C. c. canadensis Kuhl
    Canadian beaver
  • C. c. concisor
  • C. c. carolinensis Rhoads
    Carolina beaver
  • C. c. duchesnei
  • C. c. frondator Mearns
    Sonora beaver
  • C. c. idoneus
  • C. c. labradorensis
  • C. c. leucodonta Gray
    Pacific beaver
  • C. c. mexicanus Bailey
    Rio Grande beaver
  • C. c. michiganensis Bailey
    Woods beaver
  • C. c. missouriensis Bailey
    Missouri River beaver
  • C. c. pacificus Rhoads
    Washington beaver
  • C. c. pallidus
  • C. c. phaeus Heller
    Admiralty beaver
  • C. c. rostralis
  • C. c. repentinus Goldman
    Sonora beaver
  • C. c. sagittatus
  • C. c. shastensis Taylor
    Shasta beaver
  • C. c. subauratus
    California Golden beaver
  • C. c. taylori Davis
  • C. c. texensis Bailey
    Texas beaver

The North American Beaver (Castor canadensis) is the only species of beaver in the Americas, native to North America and introduced to South America. In the United States and Canada, where no other species of beaver occurs, it is usually simply referred to as beaver. Its other vernacular names, including American beaver[6] and Canadian beaver,[7] distinguish this species from the one other extant beaver, Castor fiber, native to Eurasia. ("Canadian beaver" also refers to the subspecies Castor canadensis canadensis.)

Contents

Description

This beaver is the largest rodent in North America and the third largest rodent in the world, after the South American capybara and the Eurasian beaver. Adults usually weigh 15 to 35 kg (33–77 lbs), with 20 kg (44 lbs) a typical mass, and measure around 1 m (3.3 ft) in total body length. Very old individuals can weigh as much as 45 kg (100 lbs).[8]

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 swimfins. 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 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 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, beaver were practically ubiquitous and lived from the arctic tundra to the deserts of northern Mexico.[9] Explorer David Thompson, after crossing much of North America in 1784, stated that "this Continent...from the Atlantic to the Pacific Ocean, may be said to have been in the possession of two distinct races of Beings, Man and the Beaver."[10]

Behavior

Beaver lodge, Ontario, Canada
Beaver dam, northern California, USA

Beavers are mainly active at night. They are excellent swimmers but are more vulnerable on land and tend to remain in the water as much as possible. They are able to remain submerged for up to 15 minutes. The flat, scaly tail is used to signal danger and also serves as a source of fat storage.

They construct their homes, or "lodges," out of sticks, twigs, and mud in lakes, streams, and tidal river deltas.[11] These lodges may be surrounded by water, or touching land, including burrows dug into river banks. They are well known for building dams 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. In the event of danger, a beaver slaps its tail on the water to warn other family members.

The dam is constructed using sections of deciduous trees, especially birch, aspen, willow and poplar. The inner bark, twigs, shoots and leaves of such trees are also an important part of the beaver's diet. 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.

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 disproved 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!

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 and alder. They will also eat cattails, water lilies and other aquatic vegetation, especially in the early spring (and contrary to wide-spread belief[12], 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.

Common natural predators include gray wolves, coyotes, and mountain lions. Less significant predators include bears, which can dig into a lodge, wolverines, river otters, Canadian lynx, bobcats, and mink.[13]

Subspecies

There are 25 subspecies of beaver in North America, but different subspecies have been reintroduced to areas with previously geographically isolated subspecies, following population decline or extirpation of the indigenous subspecies. This has led to very substantial mixing of the subspecies gene pools, and some subspecies may have disappeared entirely.

The most widespread subspecies are C. c. acadicus, C. c. canadensis (Canadian beaver), C. c. carolinensis (Carolina beaver), and C. c. missouriensis (Missouri River beaver).[13] The Canadian beaver originally inhabited almost all of the forested area of Canada,[14] 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 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 fomer, 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 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.[15]

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.[15]

Ecology

The beaver was trapped out and almost extirpated in North America as its fur and castoreum were highly sought after.[9] 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.[16] From 1630 to 1640, approximately 80,000 beaver were taken annually from the Hudson River and western New York.[17] 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 nineteenth 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 nineteenth and early twentieth 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.[18][19]

These animals are considered pests in some parts of their range because their dams can cause flooding in nearby areas. 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.[20] 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.[21]

The beaver is a keystone species, increasing biodiversity in its territory through creation of beaver ponds and wetlands.[22] Not only are riparian habitats enlarged as the circumference of a beaver pond is much greater than the circumference of the two banks of a stream, but aquatic plants colonize newly available watery habitat. Insect, invertebrate, fish, mammal, and bird diversity are also expanded.[23]

Effects on Bird Diversity

Canada Geese nesting on beaver lodge

Trumpeter swans (Cygnus buccinator) and Canada geese (Branta canadensis) often depend on beaver lodges as nesting sites.[23][24] 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.[25]

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 flycatchers (Empidonax spp.), tree swallows (Tachycineta bicolor), tits (Paridae spp.), wood ducks (Aix sponsa), goldeneyes (Bucephala spp.), mergansers (Mergus spp.), owls (Titonidae, Strigidae) and American kestrels (Falco sparverius).[23] 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), utilize beaver ponds for fishing. Hooded mergansers (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.[26]

Effects on Trout and Salmon

Sockeye salmon (Oncorhyncus nerka) jumping beaver dam in Alaska 1997

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 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.[27] 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.[28] 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.[29] 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.[30][31] 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.[32] Rainbow, brown and brook trout have been shown to cross as many as 14 consecutive beaver dams.[28] 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.[32] 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.[33] Downstream migration of Atlantic salmon smolts was similarly unaffected by beaver dams, even in periods of low flows.[33] 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.[34] 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. 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.[33]

Urban beavers

Beaver in Lincoln Park, Chicago 2008
After trapping, beaver lodge re-appears in Lincoln Park, Chicago Fall, 2009

After 200 years, a beaver has returned to New York City, making its home along the Bronx River, having spent time living at the Bronx Zoo as well as the Botanical Gardens.[35] Beavers were trapped to near extirpation and hadn't been seen in New York City since the early 1800s.[36] The return of "Jose", named after Representative Jose Serrano from the Bronx, is seen as evidence that efforts to restore the river have been successful.[37][38] "Jose Serrano" has been sighted below the East Tremont bridge at Drew Gardens as recently as June, 2009.[39]

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.[40] 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.[40][41][42][43] 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.[44] 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".[45] 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, lead to the return of steelhead trout and river otter in 2008, and mink in 2009.[46][47] The Martinez beavers probably originated from the Sacramento-San Joaquin River Delta which once held the largest concentration of beaver in North America.[48]

In 1999, Washington, D.C.'s annual 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.[49][50]

As introduced non-native species

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. However, the project failed and the beavers, a few pairs, 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. They are now considered a serious invasive species in the region, due to their massive destruction of forest trees, and efforts are being made for their eradication.[51] The drastically different ecosystem has led to substantial environmental damage, as the ponds created by the beavers have no ecological purpose (wetlands do not form there as they do in the beavers' native territory) and there are no native, large predators.[citation needed] They have also been found to cross saltwater to islands northward; a possible encroachment on the mainland has naturalists highly concerned. In contrast, areas with introduced beaver were associated with increased populations of native puye fish (Galaxias maculatus), whereas the exotic brook trout (Salvelinus fontinalis) and rainbow trout (Oncorhynchus mykiss) had negative impacts on native stream fishes in the Cape Horn Biosphere Reserve, Chile.[52]

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]

Despite their name, the fried pastries found in parts of Canada called beaver tails contain no beaver.

Symbolism

One of the national symbols of Canada, the beaver is depicted on the Canadian five-cent piece and was on the first Canadian postage stamp, the Three Penny Beaver. It is also the state animal of Oregon and New York, and a common school emblem for engineering schools, including the California Institute of Technology and the Massachusetts Institute of Technology, as well as the mascot for Oregon State University and the City College of New York. The beaver also appears in the coats of arms of the University of Toronto, Wilfrid Laurier University and the London School of Economics.

References

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  33. ^ a b c Collen P, Gibson RJ (2001). "The general ecology of beavers (Castor spp.), as related to their influence on stream ecosystems and riparian habitats, and the subsequent effects on fish – a review". Reviews in Fish Biology and Fisheries: 439–461. http://www.springerlink.com/content/v48769740n817601/fulltext.pdf. Retrieved Mar. 2, 2010. 
  34. ^ D. B. Sigourney, B. H. Letcher, R. A. Cunjak (2006). "Influence of Beaver Activity on Summer Growth and Condition of Age-2 Atlantic Salmon Parr". Transactions of the American Fisheries Society: 1068-1075. http://afsjournals.org/doi/abs/10.1577/T05-159.1. Retrieved Mar. 1, 2010. 
  35. ^ "New York City Beaver Returns". Science Daily. Dec. 20, 2008. http://www.sciencedaily.com/releases/2008/12/081218080817.htm. 
  36. ^ Peter Miller (Sept. 2009). "Manhattan Before New York: When Henry Hudson first looked on Manhattan in 1609, what did he see?". National Geographic. http://ngm.nationalgeographic.com/2009/09/manhattan/miller-text. 
  37. ^ Anahad O'Connor (Feb. 23, 2007). "After 200 Years, a Beaver Is Back in New York City". New York Times. http://www.nytimes.com/2007/02/23/nyregion/23beaver.html?_r=1. Retrieved Dec. 4, 2009. 
  38. ^ Trotta, Daniel. "Beaver Returns to New York City After 200 Years." World Environment News. Dec. 26, 2007.
  39. ^ Design Trust for Public Space (June 17, 2009). "Bronx River Crossing". http://designtrust.blogspot.com/2009/06/bronx-river-crossing.html. Retrieved Dec. 4, 2009. 
  40. ^ a b Boehm, Kiersten (14 Nov 2008). "Lincoln Park Beaver Relocated". Inside at Your News Chicago, IL Edition. http://www.insideonline.com/. Retrieved 4 Dec 2009. 
  41. ^ Scott Holingue (Jan. 1, 1994). Tales from an Urban Wilderness: Wildlife's Struggle for Survival in a Park Where City & Wilderness Meet. Chicago, IL: Chicago Historical Bookworks. pp. 140. ISBN 0924772255. 
  42. ^ "Park District Kills Beaver in Lincoln Park". MyFoxChicago.com. April, 2009. http://www.myfoxchicago.com/dpp/news/beaver_north_pond_apr09. Retrieved Dec. 4, 2009. 
  43. ^ John Greenfield (May 7–13, 2009). "Why are there signs that claim the Park District murdered a beaver?". Time Out Chicago. http://chicago.timeout.com/articles/museums-culture/74267/why-are-there-signs-that-claim-the-park-district-murdered-a-beaver. Retrieved Dec. 4, 2009. 
  44. ^ Carolyn Jones (April 16, 2008). "Moment of truth for Martinez beavers". San Francisco Chronicle. 
  45. ^ "Worth a Dam website". http://www.martinezbeavers.org. 
  46. ^ Aleta George (2008). "Martinez Beavers". Bay Nature Institute. http://baynature.org/articles/jan-mar-2008/ear-to-the-ground/martinez-beavers. Retrieved Nov. 6, 2009. 
  47. ^ Nicola DeRobertis-Theye. "Beavers and More in Martinez:New Habitat Thanks to Beavers". Bay Nature Institute. http://baynature.org/articles/web-only-articles/beavers-and-more-in-martinez. Retrieved Nov. 6, 2009. 
  48. ^ Thomas Jefferson Farnham (1857). Life, adventures, and travels in California. Blakeman & Co.. p. 383. http://books.google.com/books?id=cwMNAAAAIAAJ&dq=travels+in+california+farnham&printsec=frontcover&source=bl&ots=SdRWTbf-Pd&sig=MjCsrczlM3u6afZyHz-M1tP7M7s&hl=en&ei=Tez0SsHpIIXuswPf4bQG&sa=X&oi=book_result&ct=result&resnum=1&ved=0CAoQ6AEwAA#v=onepage&q=beaver&f=false. 
  49. ^ Jonathan Aiken (April 7, 1999). "Beaver is bad guy at cherry blossom time". CNN.com. http://www.cnn.com/US/9904/07/chomping.cherry.trees/index.html. Retrieved Nov. 22, 2009. 
  50. ^ Linda Wheeler (April 7, 1999). "Beaver Chomps Into Cherry Blossom Season". Washington Post. http://www.washingtonpost.com/wp-srv/local/daily/april99/chomp7.htm. Retrieved Nov. 22, 2009. 
  51. ^ CNN - Argentina eager to rid island of beavers - July 9, 1999
  52. ^ Michelle C. Moorman, David B. Eggleston, Christopher B. Anderson, Andres Mansilla, Paul Szejner (2009). "Implications of Beaver Castor canadensis and Trout Introductions on Native Fish in the Cape Horn Biosphere Reserve, Chile". Transactions of the American Fisheries Society: 306-313. http://afsjournals.org/doi/abs/10.1577/T08-081.1. Retrieved Mar. 1, 2010. 

Further reading

External links

  • 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)
  • Gallant, D., C.H. Bérubé, E. Tremblay, & L. Vasseur (2004). An extensive study of the foraging ecology of beavers (Castor canadensis) in relation to habitat quality. Canadian Journal of Zoology 82:922–933.


Castor canadensis
File:Castor
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Castoridae
Genus: Castor
Species: C. canadensis
Binomial name
Castor canadensis
Kuhl, 1820
Subspecies[2][3][4][5]
  • C. c. acadicus Bailey
  • C. c. baileyi Nelson
  • C. c. belugae Taylor
    Cook Inlet beaver
  • C. c. caecator Bangs
    Newfoundland beaver
  • C. c. canadensis Kuhl
    Canadian beaver
  • C. c. concisor
  • C. c. carolinensis Rhoads
    Carolina beaver
  • C. c. duchesnei
  • C. c. frondator Mearns
    Sonora beaver
  • C. c. idoneus
  • C. c. labradorensis
  • C. c. leucodonta Gray
    Pacific beaver
  • C. c. mexicanus Bailey
    Rio Grande beaver
  • C. c. michiganensis Bailey
    Woods beaver
  • C. c. missouriensis Bailey
    Missouri River beaver
  • C. c. pacificus Rhoads
    Washington beaver
  • C. c. pallidus
  • C. c. phaeus Heller
    Admiralty beaver
  • C. c. rostralis
  • C. c. repentinus Goldman
    Sonora beaver
  • C. c. taylori Davis
  • C. c. texensis Bailey
    Texas beaver
  • C. c. subauratus
    Golden beaver
  • C. c. sagittatus
  • C. c. shastensis Taylor
    Shasta beaver

The American beaver is the only species of beaver in the Americas, native to North America and introduced to South America. Having the Linnaean name Castor canadensis and known in Canada and the United States by the common name beaver, the species' other common names Canadian beaver (which also refers to the subspecies Castor canadensis canadensis) and North American beaver further serve to distinguish it from the other extant species of beaver, the Eurasian beaver (Castor fiber).

Contents

Description

The beaver is the largest rodent in North America and the second largest rodent in the world, after the South American capybara. Adult beavers usually weigh 15 to 35 kg (33-77 lb), with 20 kg (44 lb) a typical weight, and measure around 1 m (3.3 ft) in total body length. Very old, large beavers can weigh as much as 45 kg (100 lb).[6]

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 swimfins. 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 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 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.

Behavior

, Canada]]

Beavers are mainly active at night. They are excellent swimmers but are more vulnerable on land and tend to remain in the water as much as possible. They are able to remain submerged for up to 15 minutes. The flat, scaly tail is used to signal danger and also serves as a source of fat storage.

They construct their homes, or "lodges," out of sticks, twigs, and mud in lakes, streams, and tidal river deltas.[7] These lodges may be surrounded by water, or touching land, including burrows dug into river banks. They are well known for building dams across streams and constructing their lodge in the artificial pond which forms. The entrance to the lodge or burrow is located underwater. In the event of danger, a beaver slaps its tail on the water to warn other family members.

, USA]]

The dam is constructed using sections of deciduous trees, especially birch, aspen, willow and poplar. The inner bark, twigs, shoots and leaves of such trees are also an important part of the beaver's diet. 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. During the summer, beavers eat grasses, cattails, water lilies and other aquatic plants.

Beavers usually mate for life. The young beaver "kits" typically remain with their parents for up to two years.

Common natural predators include gray wolves, coyotes, and mountain lions. Less significant predators include bears, which can dig into a lodge, wolverines, river otters, Canadian lynx, bobcats, and mink.[8]

Subspecies

There are 25 subspecies of beaver in North America, but different subspecies have been reintroduced to areas with previously geographically isolated subspecies, following population decline or extirpation of the indigenous subspecies. This has led to very substantial mixing of the subspecies gene pools, and some subspecies may have disappeared entirely.

The most widespread subspecies are C. c. acadicus, C. c. canadensis (Canadian beaver), C. c. carolinensis (Carolina beaver), and C. c. missouriensis (Missouri River beaver).[8] The Canadian beaver originally inhabited almost all of the forested area of Canada,[9] 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. American beavers tend to be 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. American beavers have shorter nasal bones than their European cousins, with the widest point being at the middle of the snout for the fomer, and in the tip for the latter. The nasal opening for the American species is square, unlike that of the European race which is triangular. The foramen magnum is triangular in the American beaver, and rounded in the European. The anal glands of the American beaver are smaller and thick-walled with a small internal volume compared to that of the European breed. Finally, the guard hairs of the American beaver have a shorter hollow medulla at their tips. Fur colour is also different. Overall, 50% of 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.[10].

The two species are not genetically compatible. 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 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.[10]

Conservation

These animals are considered pests in some parts of their range because their dams can cause flooding in nearby areas. They are persistent in repairing any damage to the dam and the only effective measure is to remove them. In 1999, Washington, D.C.'s annual 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.[1] [2]

Non-lethal methods of containing beaver-related flooding have been developed. One such 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.

These animals are often trapped for their fur. During the early 19th century, trapping eliminated this animal from most of its original range. The beaver furs were used to make clothing and top-hats. Much of the early exploration of North America was driven by the quest for this animal's fur. Native peoples and early settlers also ate this animal's meat. The current beaver population has been estimated to be 10 to 15 million; there may have originally been ten times that many beavers in North America before the days of the fur trade.

As invasive species

, Chile]]

In the 1940s, beavers were brought to the island of Tierra Del Fuego in southern Chile and Argentina, for commercial fur production. However, the project failed and the beavers, a few pairs, 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. They are now considered a serious invasive species in the region, due to their massive destruction of forest trees, and efforts are being made for their eradication.[11] The drastically different ecosystem has led to substantial environmental damage, as the ponds created by the beavers have no ecological purpose (wetlands do not form there as they do in the beavers' native territory) and there are no native, large predators. They have also been found to cross saltwater to islands northward; a possible encroachment on the mainland has naturalists highly concerned.

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.Template:Fact In parts of North America, fried pastries called beaver tails may be found. Despite their name, they contain no beaver.

Symbolism

One of the national symbols of Canada, the beaver is depicted on the Canadian five-cent piece and was on the first Canadian postage stamp, the Three Penny Beaver. It is also the state animal of Oregon and New York, and a common school emblem for engineering schools, including the California Institute of Technology and the Massachusetts Institute of Technology, as well as the mascot for Oregon State University. The beaver also appears in the coats of arms of the University of Toronto and the London School of Economics.

References

  1. Linzey, A. V. & NatureServe (Hammerson, G. & Cannings, S.) (2008). Castor canadensis. 2008 IUCN Red List of Threatened Species. IUCN 2008. Retrieved on 6 January 2009.
  2. MSW Synonym List. Mammal Species of the World. Smithsonian Institution, 1993.
  3. Warner, Richard E. and Kathleen M. Hendrix, editors. California Riparian Systems: Ecology, Conservation, and Productive Management University of California Press, 1984, p. 952. Retrieved on 2007-08-04.
  4. Browse Genus equals Castor by Scientific Name for All Museums. Berkeley Natural History Museums. Retrieved on 2007-08-04.
  5. 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 2007-08-04.
  6. http://www.adfg.state.ak.us/pubs/notebook/furbear/beaver.php
  7. "Scientist discovers beavers building prime salmon habitat in Skagit Delta". The Seattle Times. May 18, 2009. http://seattletimes.nwsource.com/html/localnews/2009231736_beavers18m.html. 
  8. 8.0 8.1 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 2007-08-04.
  9. Kieffer, Michael Meadows in Mist Bull Run Mountains Conservancy, Inc. Retrieved on 2007-08-04.
  10. 10.0 10.1 Kitchener, Andrew (2001). Beavers. p. 144. ISBN 187358055X. 
  11. CNN - Argentina eager to rid island of beavers - July 9, 1999

Further reading

External links

  • 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)
  • Gallant, D., C.H. Bérubé, E. Tremblay, & L. Vasseur (2004). An extensive study of the foraging ecology of beavers (Castor canadensis) in relation to habitat quality. Canadian Journal of Zoology 82:922–933.


Wiktionary

Up to date as of January 14, 2010

Definition from Wiktionary, a free dictionary

Contents

English

an American beaver

Noun

Singular
American beaver

Plural
American beavers

American beaver (plural American beavers)

  1. (uncountable) A species of beaver, Castor canadensis, native of North America.
  2. (countable) An individual of this species.

Translations

External links


Simple English

Redirecting to Beaver








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