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Beaver
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.
Beaver skulls and teeth are disproportionately large. This is
crucial for cutting through hard woods like maple and oak. Most
notably, 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.
Reproduction
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 environment.
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.
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.
Lifespan/Longevity
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.
Behavior
Beavers usually live in family groups of up to 8 related individuals
called colonies. The younger siblings stay with their parents for up
to 2 years, helping with infant care, food collection, and dam
building. Beaver families are territorial and defend against other
families. One method is territory marking. This is done by making
mud piles around the edges of a territory, and then by depositing
anal and castoral secretions on these piles. Beavers will also warn
others of danger by slapping their tales against the water, creating
a powerful noise. This, however, is not always effective, as older
beavers will often ignore the warning slaps of younger members of
the colony.
Beavers are primarily nocturnal. They are only occasionally seen
during the day, usually around dusk. Beavers travel good distances
from their homes to find food. If they find a good source, they
build canals to the food source as a way to float the food back to
their lodges. Logs and twigs are often stored underwater for winter
feeding.
Beavers build dams to slow down the flow of water in streams and
rivers and then build stable lodges for shelter. The dams are
engineered according to the speed of the water; in slow water the
dam is built straight, but in fast water the dam is built with a
curve in it. This provides stability so that the dam will not be
washed away.
Food Habits
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."
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