|
Beaver ( Benjamin Beaver)
Beavers
are semi-aquatic
rodents native to
North America and
Europe. They are the only 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.
Beavers are best known for their
natural trait of building
dams in
rivers and
streams, and building
lodges in the eventual artificial
pond. They are the second largest rodents, after the
capybara.
Adult
specimens weighing over 25
kg are not uncommon.
Species
The
European Beaver (Castor fiber) 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 thousands live on the
Elbe, the
Rhone and in parts of
Scandinavia. 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
American Beaver (C. canadensis) is the
national animal of
Canada; in fact, it is depicted on the Canadian five-cent piece and was on
the first Canadian
postage stamp, the Three Penny Beaver. However, in several areas of that
country, it is considered a
pest. It is also the state animal of
Oregon, the
state mammal of
New York (after the historical emblem of
New Netherland) and the mascot of
Oregon State University. It is also a common school emblem for
engineering schools, including the
California Institute of Technology and the
Massachusetts Institute of Technology. It is also an emblem for
London School of Economics and the name of its student newspaper -
The Beaver.
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, about 10,000 years ago.
Beaver tree
Dams
The dams are created both as a
protection against predators (bear
is the only natural predator) and to provide easy access to food during winter.
It is the sound of water in motion that stimulates the beavers to build[2],
and if for example a pipe is placed under the dam to drain it the beavers will
not do anything about it. However they repair any damage to the dam and build it
higher as long as the sound is there. Conversely, beavers will attempt to build
dams in response to recordings of water flowing even in the absence of water.
The ponds created by
well-maintained dams help isolate the beavers' home, their lodge, also
created from severed branches and other natural sources. The lodge has an
underwater entrance to make entry nearly impossible for any other animal
(however,
muskrats have been seen living inside beaver lodges with the beavers who
made it).
Destroying a beaver dam without
removing the beavers takes a lot of effort.
Recent studies involving beaver
habitual activities have indicated that beavers may respond to a 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 do so after a
considerable period of time. Additionally the beavers, when faced with a pipe
allowing water to pass through their dam, initially try ineffective measures but
eventually stoped 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 thus emmiting no noise of running
water.
Fur Trade
Beaver pelts were used as
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 lead to their endangerment. Eventually, the
fur trade fell apart due to declining demand in Europe and the take over of
trapping grounds to support the growing agriculture sector.
Popular culture
Popular western culture typically
depicts the animal positively as a good natured and industrious character such
as Mr. and Mrs Beaver who are important heroic characters in the classic
fantasy novel,
The Lion, the Witch and the Wardrobe. Since the animal in a
national symbol of
Canada, 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" ( friend in
Algoquin).
The true beaver (Castor fiber)
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.
Dams
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
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
A beaver lodge
north of
Saguenay, Quebec
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
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.
| 
This
web site is best viewed when your monitor is set at 1024 X 768
