The beaver is North America's largest
rodent. Adults may be 4 feet long and weigh over 60 pounds. A beaver is
easy to identify because of its large size, its distinctive webbed hind
feet and its large flat tail that resembles the end of a canoe paddle.
The tail is nearly hairless and is a dull-black colour. The "splat" that
the tail makes when slapped on the water is one of the most distinctive
of nature's sounds. The beaver's body fur is dark brown on its back and
sides, and a light brown on its chest and belly. Its front feet are short
and have heavy claws, and possess good dexterity for feeding, grooming,
digging and lodge construction. Its hind legs are large and have fully
webbed feet which propel it through the water when it is swimming.
Like the muskrat's, the beaver's fur
is virtually waterproof, and provides the protection and buoyancy necessary
for the animal's extended underwater activities. The beaver's eyes are
small in proportion to its body size, allowing moderate vision both under
and above water. It has well-developed senses of smell and hearing, and
its nose and ears have valvular processes which close tightly under water.
There is a similar valvular process in its mouth behind the incisor teeth,
which allows the beaver to gnaw while underwater.
The beaver also possesses a specialized
digestive system to help it digest tree bark, and a special respiratory
adaptation which gives it the capability to remain submerged for nearly
20 minutes. These specialized physiological and morphological adaptations
serve both positive and negative functions; they have made the beaver well
suited for a specific environment, but have also restricted it to very
narrow habitat tolerances.
The beaver has two chisel-like incisors
in its upper and lower jaws that grow constantly and are very effective
tree cutting tools. These teeth are both self-sharpening and ever-growing,
which means the beaver must use them continually to maintain their proper
length and sharpness.
Beavers are found throughout Canada
and played a vital role in establishing this country's Fur Trade.
The engineering skills possessed by
beavers are well known. They are particularly adept at building dams, and
may construct them across narrow, flowing waters, such as shallow streams
and the channels of larger rivers.
When a beaver cuts a tree, he usually-starts
by gnawing a notch at an easy-to-reach height, then goes to the opposite
side of the tree and gnaws another a few inches below the first. He continues
chewing the bark and wood away from between the two notches until the tree
falls. The only way the beaver can control where the tree falls is by the
position of the notches he chews in the tree's trunk. In addition to building
the dam and lodge, beavers often form waterways so they can float food
and building materials from one area to another.
Beavers are primarily bark-eaters,
and ingest the bark of young twigs, and new growth of wood found between
the outer bark and the wood of tree branches and trunks. In spring and
fall, about half of the beaver's food is made up of woody vegetation. In
summer it eats little woody vegetation, but in winter it feeds on it almost
exclusively. It also eats corn and other row crops when they are available,
as well as various water plants.
As fall approaches, the beaver begins
to actively cut trees and shrubs for the colony's food cache. The quantity,
quality and availability of this under-ice food supply will determine the
condition and survival of the colony.
Beavers reproduce once a year, with
mating activity beginning in January when rivers and wetlands are covered
with ice. A 107 to 110 day gestation period follows, with an average of
three to four young usually born in May. At birth the kits (young beavers)
are fully furred, have their eyes open and incisor teeth visible. Kits
are seldom seen until they are about one month old, though they are able
to swim at birth, and are capable of being weaned in six to eight weeks.
Although weaned within three months, the young usually remain with the
family unit or colony for up to two years before leaving to establish a
colony of their own. Typically, these two-year-olds will disperse, pair,
establish territories, and raise their first litters at three years of
age. However, under favourable conditions, they will produce their first
litters at two years of age. The average lifespan of a beaver in the wild
is three to four years. However, it is not uncommon to find eight-year-olds
and rare individuals may reach or exceed 15 years of age