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Beaver

2007 Schools Wikipedia Selection. Related subjects: Mammals

   iBeavers

                     Fossil range: Late Miocene - Recent

   American Beaver
   American Beaver
                Scientific classification

   Kingdom: Animalia
   Phylum:  Chordata
   Class:   Mammalia
   Order:   Rodentia
   Family:  Castoridae
   Genus:   Castor
            Linnaeus, 1758

                                   Species

   C. canadensis
   C. fibre

   Beavers are semi-aquatic rodents native to North America and Europe.
   They are the only living members of the family Castoridae, which
   contains a single genus, Castor. Genetic research has shown the
   European and North American beaver populations to be distinct species
   and that hybridization is unlikely.

General

   Beavers are best known for their natural trait of building dams in
   rivers and streams, and building their homes (aka lodges) in the
   eventual artificial pond. They are the second-largest rodent in the
   world (after the capybara).

   Beavers continue to grow throughout life. Adult specimens weighing over
   25 kg (55 lb) are not uncommon. Females are as large as or larger than
   males of the same age, which is uncommon among mammals.

Species

   A beaver skull
   Enlarge
   A beaver skull

   The European Beaver (Castor fibre) was hunted almost to extinction in
   Europe, both for fur and for castoreum, a secretion of its scent gland
   believed to have medicinal properties. However, the beaver is now being
   re-introduced throughout Europe. Several thousand live on the Elbe, the
   Rhone and in parts of Scandinavia. In northeast Poland there is a
   thriving community of Castor fibre. They have been reintroduced in
   Bavaria and The Netherlands and are tending to spread to new locations.
   The beaver finally became extinct in Great Britain in the sixteenth
   century: Giraldus Cambrensis reported in 1188 (Itinerarium ii.iii) that
   it was to be found only in the Teifi in Wales and in one river in
   Scotland, though his observations are clearly first hand.

   In October 2005, six European beavers were re-introduced to Britain in
   Lower Mill Estate in Gloucestershire, and there are plans for
   re-introductions in Scotland and Wales.

   The extinct North American Giant beaver (Castoroides ohioensis) was one
   of largest rodents that ever evolved. It disappeared, with other large
   mammals in the Holocene extinction event, which began about 13,000
   years ago.

Habitat

   Canoeists try unsuccesfully to run a beaver dam in Algonquin Park. The
   dam is about about 1m high.
   Enlarge
   Canoeists try unsuccesfully to run a beaver dam in Algonquin Park. The
   dam is about about 1m high.

   The habitat of the beaver is the riparian zone inclusive of stream bed.
   The habit of the beaver for hundreds of thousands of years in the
   Northern Hemisphere has been to keep these watery systems healthy and
   in good repair, although to a human observer, seeing all of the downed
   trees, it might sometimes seem that the critters are doing just the
   opposite. Beaver work as a keystone species in an ecosystem by creating
   wetlands that are utilized by many other species. The ability of
   beavers to radically alter landscape is amazing. Next to humans, no
   other extant animal does more to shape its landscape. Introduced to an
   area without its natural predators, as in Tierra del Fuego, beavers
   have flooded thousands of acres of land and are considered an
   unstoppable plague. One notable difference in Tierra del Fuego from
   most of North America is that the trees found in Tierra del Fuego do
   not coppice as do the Willows, Poplars, Aspens etc of North America.
   Thus the "damage" by the beavers seems more severe.

Dams

   The dams are created both as a protection against predators, e.g.,
   coyotes, wolves and bears, and to provide easy access to food during
   winter. It is both the sound of water in motion and the current that
   stimulates the beavers to build. If, for example, a pipe is placed
   under the dam to drain it the beavers may stuff it with a tree trunk
   unless the pipe inlet is protected with a large cage-like filter. They
   may repair any damage to the dam and build it higher as long as the
   sound continues. However, in times of high water, they often allow
   spillways in the dam to flow freely. Beavers have even attempted to
   build dams in response to recordings of water flowing even in the
   absence of water.

   Destroying a beaver dam without removing the beavers takes a lot of
   effort, especially if the dam is downstream of an active lodge. Beavers
   can rebuild such primary dams overnight, but may not defend secondary
   dams as vigorously.
   Trees, up to 250 mm (10 in) in diameter, felled by beavers in one
   night.
   Enlarge
   Trees, up to 250 mm (10 in) in diameter, felled by beavers in one
   night.

   Recent studies involving beaver habitual activities have indicated that
   beavers may respond to an array of stimuli, not just the sound of
   running water. In two experiments Wilson (1971) and Richard (1967,
   1980) demonstrate that although beavers will pile material close to a
   loudspeaker emitting sounds of water running, they only do so after a
   considerable period of time. Additionally the beavers, when faced with
   a pipe allowing water to pass through their dam, eventually stopped the
   flow of water by plugging the pipe with mud and sticks. The beavers
   were observed to do this even when the pipe extended several meters
   upstream and near the bottom of the stream and thus produced no sound
   of running water.

   Beaver dams can be disruptive; the flooding can cause extensive
   property damage, and when the flooding occurs next to a railroad
   roadbed, it can cause derailments by washing-out under the tracks, or
   when a beaver dam bursts and the resulting flash flood overwhelms a
   culvert. This disruption is not limited to human geography; beavers can
   destroy nesting habitat for endangered species, and often destroy
   mature trees for which they have no use.

   Yet dam building activity restores wetlands, the land's most beneficial
   ecosystem. Such wetland benefits include flood control downstream,
   biodiversity (by providing habitat for many rare as well as common
   species), and water cleansing, both by the breakdown of toxins such as
   pesticides and the retention of silt by beaver dams. The latter also
   reduces erosion as well as decreasing turbidity that is the limiting
   factor for aquatic life. While beavers can create damage, part of the
   problem is one of perception and time scale. The damage beavers do such
   as the undermining of a roadway or the drowning of some trees is very
   visible very shortly after the beavers activity in an area starts. The
   benefits, mentioned below, are long term and not easily seen except by
   someone who is monitoring a catchment and realizes what huge positive
   effects beavers cause.
   Beaver lodge, approx. 20 foot diameter. Ontario, Canada
   Enlarge
   Beaver lodge, approx. 20 foot diameter. Ontario, Canada

   The beaver's effects on the environment go beyond what you would expect
   of a rotund, buck toothed rodent. The first part of his influence is
   felt when his dam creates a pond.

   Flood control

   A beaver dam has a certain amount of free board so when heavy rains
   occur, the dam fills up and gradually releases the extra stored water.
   Often this is all that is necessary to reduce the height of the flood
   wave moving down the river and will reduce or eliminate damage to human
   structures. But flood control is achieved in other ways as well. The
   surface of a stream intersects the surrounding water table. By raising
   the level of a stream in a certain area, the gradient of the surface of
   the water table is reduced and water by the beaver dam flows more
   slowly into the stream. This effect not only helps to reduce flood
   waves but also increases the water flow when there is no rain. The
   other way beaver dams smooth out water flow is by increasing the wetted
   area of the stream. This allow more water to seep into the underlying
   ground where its flow is slowed down. This water eventually finds its
   way back to the stream. Rivers with beaver dams in their head waters
   have lower high water and higher low water.
   Drained Beaver Dam. Allegheny State Park
   Enlarge
   Drained Beaver Dam. Allegheny State Park

   Beaver Control

   Wetland creation

   If a beaver pond becomes too shallow due to the settling out of
   sediment or if the tree supply runs out in an area, the beavers will
   abandon the site. Eventually the dam, without the beaver to maintain
   it, will be breached and the water will drain out. The rich thick layer
   of silt, branches, dead leaves etc. behind the old dam is the ideal
   habitat for wetland species. Many of them will have been on the fringes
   of the pond. Wetlands have significant environmental benefits.

   The grazing meadow (vega)

   As the wetland fills and dries out, pasture species colonize it and it
   becomes a meadow suitable for grazing. In an area with nothing but
   forest down to the stream edge, this provides a valuable niche for many
   animals which otherwise would be excluded.

   The riverine forest

   And finally the meadow will be colonized by riverine trees, typically
   aspens, willows and such species which are favoured by the beaver. At
   this point the beavers are likely to recolonize the area and the cycle
   starts over again.

   Bottom land

   As can be seen by the above, each time this process repeats itself,
   another layer of rich organic soil is added to the bottom of the
   valley. The valley slowly fills up and the flat area at the bottom gets
   wider and wider. Research is sparse on this topic, but it seems likely
   that much of the fabled bottom land in North America was created, or at
   least added to, by the efforts of the generations of beavers which
   lived there.

   Nutrient removal

   The removal of nutrients from the stream flow by beaver ponds is an
   interesting and very valuable process. Farming along the banks of
   rivers often increases the loads of phosphates, nitrates and other
   nutrients and these cause problems downstream when this water is
   extracted for drinking. Besides silt, the beaver dam collects twigs and
   branches from the beavers activity and leaves, notably in the fall. The
   main component of this material is cellulose, a polymer of β-glucose
   monomers (This creates a more crystalline structure than is found in
   starch, which is composed of α-glucose monomers. Cellulose is a type of
   polysaccharide.). Many bacteria produce cellulase which can split off
   the glucose and use it for energy. Just as algae get their energy from
   sunlight, these bacteria get their energy from cellulose and they form
   the base of a very similar food chain. However a source of energy is
   not enough for growth. These bacteria are hungry for every molecule of
   nitrogen and phosporous they can grab. In this way, these, and other
   nutrients are fixed into the beaver pond and the surrounding ecology
   and removed from the stream. The capture of these nutrients helps to
   explain the great richness of the resulting bottom land.

   Pesticide and herbicide removal

   Agriculture also introduces herbicides and pesticides into our streams.
   Bacteria are an extremely variable lot and some of these toxicants are
   metabolized and decomposed by the bacteria in the cellulose rich bottom
   of a beaver dam.

   Denitrification

   Some scientist believe that the nitrate cascade, the production of far
   more fixed nitrogen than the natural cycles can turn back into nitrogen
   gas, may be as much of a problem to our ecology as carbon dioxide
   production. It is likely, but not proven, that beaver dams along a
   stream may contribute to denitrification. In sewage plants,
   denitrification is achieved by passing the water through successive
   aerobic and anaerobic stages. Under a beaver dam, as the water seeps
   down into the soil, the oxygen is used up by the fauna in the rich
   organic layer. At some point all the oxygen is used up and the soil
   becomes anaerobic. This water eventually finds its way into the stream
   and into another beaver dam. This aerobic, anaerobic cycle continues
   all the way down the stream.

   Beavers have been known to build very large dams, the largest known was
   discovered near Three Forks, Montana and was 2,140 feet long, 14 feet
   high, and 23 feet thick at the base. When objectionable beaver flooding
   occurs, modern water level control devices can be installed for a
   cost-effective and environmentally sound solution. Unwanted damage to
   trees can be prevented by wrapping chicken wire or sheet metal around
   the base of trees.

Lodges

   The ponds created by well-maintained dams help isolate the beavers'
   home, their lodge, which is also created from severed branches and mud.
   The lodge has underwater entrances to make entry nearly impossible for
   any other animal (however, muskrats have been seen living inside beaver
   lodges with the beavers who made it). A very small amount of the lodge
   is actually used as a living area. Contrary to popular belief, beavers
   actually dig out their den with an underwater entrance after they
   finish building the dam and lodge structure. There are typically two
   dens within the lodge, one for drying off after exiting the water, and
   another, drier one where the family actually lives.

Danger signal

   When startled or frightened, a swimming beaver will rapidly dive while
   forcefully slapping the water with its broad tail. This creates a loud
   'slap', audible over large distances above and below water. This noise
   serves as a warning to other beavers in the area. Once a beaver has
   made this danger signal, all nearby beavers will dive and may not
   reemerge for some time.

Fur trade

   Beaver pelts were used for barter by Native Americans in the 17th
   century to gain European goods. They were then shipped back to Great
   Britain and France where they were made into clothing items. Widespread
   hunting and trapping of beavers led to their endangerment. Eventually,
   the fur trade fell apart due to declining demand in Europe and the
   takeover of trapping grounds to support the growing agriculture sector.
   A small resurgence in beaver trapping has occurred in some areas where
   there is an over-population of beaver; trapping is only done when the
   fur is of value, and normally the remainder of the animal is also
   utilized as animal feed.

In culture

   A North American Beaver at the Toronto Zoo
   Enlarge
   A North American Beaver at the Toronto Zoo

   Popular western culture typically depicts the animal positively, as a
   good-natured and industrious character.
     * Mr. and Mrs. Beaver who are important heroic characters in the
       classic fantasy novel, The Lion, the Witch and the Wardrobe.

     * The beaver's habits, habitat and conservation status (as of 1908)
       are recurring themes in The Tent Dwellers, by Albert Bigelow Paine.
       Lillian Hoban's Charlie the Tramp is a children's book about a
       young beaver and his family.

     * The North American Beaver (C. canadensis) is the national animal of
       Canada; it is depicted on the Canadian five-cent piece and was on
       the first Canadian postage stamp, the Three-Penny Beaver. As a
       national symbol, the animal is a favourite choice for depicting
       Canadians as furry characters and was chosen to be the mascot of
       1976 Summer Olympics held in Montreal with the name "Amik"
       ("beaver" in Algonquin). It is also the symbol of many units and
       organizations within the Canadian Forces, such as on the cap badges
       of the Royal 22e Régiment and the Canadian Military Engineers.
       However, beavers are considered a pest by some people.

     * There is typically a Beaver Patrol in the Boy Scouts of America's
       Wood Badge adult-leadership training program.

     * Oregon is known as the "The Beaver State." The beaver is the state
       animal and its likeness appears on the state flag. It is the state
       mammal of New York (after the historical emblem of New Netherland).

     * Due to its engineering capabilities, the beaver serves as the
       mascot of the Massachusetts Institute of Technology, California
       Institute of Technology, Oregon State University and the University
       of Toronto. It is also an emblem for London School of Economics and
       the name of its student newspaper, The Beaver.

     * In the 17th century, based on a question raised by the Bishop of
       Quebec, the Roman Catholic Church ruled that the beaver was a fish.
       The legal basis for the decision probably rests with the Summa
       Theologica of Thomas Aquinas, which bases animal classification as
       much on habit as anatomy. Therefore, the general prohibition on the
       consumption of meat on Fridays during Lent did not apply to beaver
       meat.

     * In the Cheese Shop sketch of Monty Python's Flying Circus, a
       famished customer asks the proprietor of a cheese shop for any one
       of dozens of different kinds of cheese, including the nonexistent
       Venezuelan Beaver Cheese. Venezuela has no indigenous beavers.

     * Nickelodeon aired The Angry Beavers, a popular children's
       television show.

     * Bell Canada features two beavers called Frank and Gordon in
       television ads.

     * The Norwegian municipality of Åmli has a beaver in its
       coat-of-arms.

1911 encyclopedia text

   Beaver tracks in snow, in Ontario. Hind paws approx 20cm long.
   Enlarge
   Beaver tracks in snow, in Ontario. Hind paws approx 20cm long.

   The following text is taken from the 1911 Encyclopedia Brittannica.

   Beaver, the largest European aquatic representative of the mammalian
   order RODENTIA, easily recognized by its large trowel-like, scaly tail,
   which is expanded in the horizontal direction.

   The word is descended from the Aryan name of the animal, cf. Sanskrit
   babhru's, brown, the great ichneumon, Lat. fibre, Ger. Biber, Swed.
   bäver, Russ. bobr'; the root bhru has given "brown," and, through
   Romanic, "bronze" and "burnish."

   The true beaver (Castor fibre) is a native of Europe and northern Asia,
   but it is represented in North America by a closely-allied species (C.
   canadensis), chiefly distinguished by the form of the nasal bones of
   the skull.
   Yellowstone National Park.
   Enlarge
   Yellowstone National Park.

   Beavers are nearly allied to the squirrels (Sciuridae), agreeing in
   certain structural peculiarities of the lower jaw and skull. In the
   Sciuridae the two main bones (tibia and fibula) of the lower half of
   the leg are quite separate, the tail is round and hairy, and the habits
   are arboreal and terrestrial. In the beavers or Castoridae these bones
   are in close contact at their lower ends, the tail is depressed,
   expanded and scaly, and the habits are aquatic.
   Tierra del Fuego.
   Enlarge
   Tierra del Fuego.

   Beavers have webbed hind-feet, and the claw of the second hind-toe
   double. They have poor eyesight, but a keen sense of hearing, smell,
   and touch.

   In length beavers--European and American--measure about 2 ft. exclusive
   of the tail, which is about 10 inches long. They are covered with a fur
   to which they owe their chief commercial value; this consists of two
   kinds of hair--the one close-set, silky and of a greyish colour, the
   other much coarser and longer, and of a reddish brown.

   Beavers are essentially aquatic in their habits, never travelling by
   land unless driven by necessity. Formerly common in England, the
   European beaver has not only been exterminated there, but likewise in
   most of the countries of the continent, although a few remain on the
   Elbe, the Rhone and in parts of Scandinavia. The American species is
   also greatly diminished in numbers from incessant pursuit for the sake
   of its valuable fur.

   Beavers are sociable animals, living in streams, where, so as to render
   the water of sufficient depth, they build dams of mud and of the stems
   and boughs of trees felled by their powerful incisor teeth. In the
   neighbourhood they make their "lodges," which are roomy chambers, with
   the entrance beneath the water. The mud is plastered down by the
   fore-feet, and not, as often supposed, by the tail, which is employed
   solely as a rudder.

   They are mainly nocturnal, and subsist chiefly on bark and twigs or the
   roots of water plants.
   Fossil Butte National Monument.
   Enlarge
   Fossil Butte National Monument.

   The dam differs in shape according to the nature of particular
   localities. Where the water has little motion it is almost straight;
   where the current is considerable it is curved, with its convexity
   towards the stream. The materials made use of are driftwood, green
   willows, birch and poplars; also mud and stones intermixed in such a
   manner as contributes to the strength of the dam; but there is no
   particular method observed, except that the work is carried on with a
   regular sweep, and that all the parts are made of equal strength.

   "In places," writes Hearne, "which have been long frequented by beavers
   undisturbed, their dams, by frequent repairing, become a solid bank,
   capable of resisting a great force both of ice and water; and as the
   willow, poplar and birch generally take root and shoot up, they by
   degrees form a kind of regular planted hedge, which I have seen in some
   places so tall that birds have built their nests among the branches."

   Their houses are formed of the same materials as the dams, with little
   order or regularity of structure, and seldom contain more than four
   old, and six or eight young beavers. It not unfrequently happens that
   some of the larger houses have one or more partitions, but these are
   only posts of the main building left by the builders to support the
   roof, for the apartments have usually no communication with each other
   except by water.
   Lassen Volcanic National Park.
   Enlarge
   Lassen Volcanic National Park.

   The beavers carry the mud and stones with their fore-paws and the
   timber between their teeth. They always work in the night and with
   great expedition. They cover their houses late every autumn with fresh
   mud, which, freezing when the frost sets in, becomes almost as hard as
   stone, so that neither wolves nor wolverines can disturb their repose.

   The favourite food of the American beaver is the water-lily ( Nuphar
   luteum), which bears a resemblance to a cabbage-stalk, and grows at the
   bottom of lakes and rivers. Beavers also gnaw the bark of birch, poplar
   and willow trees; but during the summer a more varied herbage, with the
   addition of berries, is consumed.

   When the ice breaks up in spring they always leave their embankments,
   and rove about until a little before the fall of the leaf, when they
   return to their old habitations, and lay in their winter stock of wood.
   They seldom begin to repair the houses till the frost sets in, and
   never finish the outer coating till the cold becomes severe. When they
   erect a new habitation they fell the wood early in summer, but seldom
   begin building till towards the end of August.

   Castoreum is a substance contained in two pear-shaped pouches situated
   near the organs of reproduction, of a bitter taste and slightly foetid
   odour, at one time largely employed as a medicine, but now used only in
   perfumery.

   Fossil remains of beavers are found in the peat and other superficial
   deposits of England and the continent of Europe; while in the
   Pleistocene formations of England and Siberia occur remains of a giant
   extinct beaver, Trogontherium cuvieri, representing a genus by itself.
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