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Eurasian beaver
Norway, France, Poland, Germany, Eastern Europe, Siberia, and
other Scandinavian countries. Freshwater lakes and rivers, usually
near woodlands, in the palearctic region.
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Eurasian beaver
Castor fiber has a body length of 2.6 to 3.6 ft and a tail length of
12 to 13.6 in, making it one of the world's largest rodents. Its
shoulder height is 12 to 14 inches and it weighs 37 to 70 lbs. The
European beaver has very little sexual dimorphism; the average male
weighs about 54 lbs and is 3 ft long, while the average female
weighs 58 lbs and is 3.2 ft long. Beavers have stocky bodies with
flattened hairless tails known as scoops. They have swimming
membranes between their toes and can use both forelegs like hands.
The European beaver has very prominent incisors. It has a thick coat
of fuzzy and straight hair that ranges from a rich glossy brown to a
yellowish brown on the upperparts, and from brown to tawny on the
under parts. Its small eyes have nictitating membranes and its ears
and nostrils are valvular.
Reproduction
The average gestation period of the European beaver is 105 days.
Beavers have a single annual breeding season. Mating occurs in
January and February and births occur between April and June. The
estrous cycle of the female lasts 2 weeks and the female is
receptive for 10 to 12 hours. The litter size is from 1 to 5 and the
average number of babies is 3. The average birth weight is 1 lb.
Weaning occurs after 3 months, but independent minor food intake by
babies can occur after just 2 weeks. The babies stay in the lodge
for the first week or two and the mother must force them to go into
the water for the first time. The young often have a hard time
adjusting to the change from their mother's milk to eating bark and
many do not survive this period. If they do survive, they encounter
few natural threats for the remainder of their lives. Castor fiber
reaches sexual maturity in 2.5 to 3 years. The life span of the
European beaver is about 10 years in the wild, but they may live up
to 17 years of age. In captivity beavers have reached 35 years of
age.
Behavior
Beavers are social animals and live in family groups of 5 to 8
animals. The group consists of an older couple that owns the
territory and the litter from the current year and the previous
years. Beavers are monogamous and the female is dominant. The
territory of a family group is from .2 to 1.8 miles along a river
bank or shoreline. The beavers rarely go more than 64 feet from the
water. Their territories are usually permanent. The European beaver
marks its territory by making scent mounds that are 30 cm high and 1
m across. The mounds are made of mud and sticks and branches. The
beavers have 2 anal glands that secrete a castoreum oil. This oil
has a musk odor and is deposited on the scent mounds. The oil is
also used to grease the beaver's fur coat to make it water
repellent. The beaver also has specialized cleaning claws on the
second toe of its hind legs that are used for brushing the coat.
Beavers may migrate during the fall in order to find food. They are
unable to reach buds and branches high in trees, so they cut the
trees down by gnawing at the trunk. When gnawing, a beaver stands
upright supported by its tail. The gnawing process gives a tree
trunk the well known hourglass shape. Beavers are generally
nocturnal and may cut down a tree that is 16 inches in diameter in
one night.
European beavers build "lodges" made of sand and clay. These lodges
are usually a simple tube in the river bank that feeds into the
water below the surface. If the river bank is not high enough to
build a lodge, then the beaver builds a castle on the river bank.
This castle is made by piling up branches and twigs and fastening
them with mud. In order to keep the entrance to the lodge
underwater, beavers keep the water level up by building dams. These
famous waterlevel-regulating dams are built by driving thick sticks
into the mud and filling the spaces with branches and mud. They can
be anywhere from 16 to 96 feet in length. These dams create a good
environment for many living things, including the particular trees
that beavers eat.
Beavers love to dive and swim and are well adapted for these
activities. Their thick water-repellant coat keeps them dry and warm
while their webbed feet and flat tail are ideal for swimming. A
beaver usually stays underwater for two to three minutes but can
dive for as long as fifteen minutes.
European beavers communicate with each other using scent, posture,
tail slaps, and several calls that sound like whistling and whining.
The tail slap is used to warn others of danger. The beaver just
slaps its tail against the water while it is diving to make the
call.
Food Habits
The European beaver is strictly herbivorous. Its diet consists of
hundreds of species of water and river bank plants such as tubers
and the rootstocks of myrtles, cattails, and water lilies. Beavers
also eat trees. They prefer aspen trees but also eat hazels, black
poplars, lime trees, and other softwood barks. Alder and oak trees
are never eaten and used only for constructional purposes. The large
teeth and strong bite assist the beaver in biting and chewing its
food. Long appendices help beavers to digest their high cellulose
bark diets. Their food intake per day is about twenty percent of
their body weight. Microorganisms break up the nutritional mush of
bark that the beaver swallows and build up bacterial proteins that
the beaver can digest. A beaver eats only a few species of trees,
and if its diet changes it must make a gradual change so that the
microorganisms can adjust to the new diet.
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