The hind feet of beaver are fully
webbed, and large. These feet often measure 6 inches
in length, and the spread of the toes is equal to or
greater than the length as the beaver swims. Five
toes with strong nails are found on the hind feet,
including unique split toenail on one toe which
serves the beaver as a comb for grooming. The front
feet seem small in contrast to the hind feet. These
feet measure 2 1/2 to 3 inches in length and are not
webbed at all. Beaver normally swim with their front
feet held against their chest, and the large webbed
hind feet provide the propulsion with the tail
acting as a rudder.
Guard hairs in beaver fur are 2
inches in length, overlaying a soft and dense
underfur about an inch deep. Colors vary from
section to section, and from blonde colors to nearly
black. Both male and female beaver have large
glands, called castors, beneath the skin on the
lower bellies. These glands produce an oil which the
beaver combs into its fur to waterproof it. This oil
is also deposited by the beaver at selected
locations as territorial markers or mating
attractants in the spring of the year.
Beaver have transparent eyelids
which cover the eyes as the beaver submerges,
enabling the beaver to see well when submerged as
the eyeball is protected from abrasive particles
suspended in the water. The ears and nose of a
beaver have valves that close as a beaver submerges,
preventing the entry of water. Two upper and two
lower incisor teeth dominate the front of a beaver's
mouth. The upper incisors overlap the lower
incisors, and friction from chewing causes the teeth
to self-sharpen to chisel sharpness.
Similar to birds and reptiles,
beaver have a single lower body opening, known as a
cloaca. This single opening serves the urinary and
bowel tracts, the secreted oil from the castor
glands, and covers the reproductive organs of both
males and females.
Reproduction
Beaver usually live
in family units consisting of the older mated pairs,
young from the previous year, and young from the
current season called kits. Breeding season takes
place in late January or February in most states.
Young from the previous year are about 22 months of
age at this time and they are evicted from the
colony to relocate and seek mates of their own. The
gestation period of beaver is 107 days and the adult
male and kits usually take up a temporary residence
in a bank den while the new litter is being born in
April, May or June. The birthing process may take
several days, and 3 to 5 kits are a typical litter
size. Beaver kits are fully furred when born, their
eyes are open, and the incisor teeth are visable.
Newborn beaver kits take to the water easily, and
they might be swimming before they are one day old.
Most adult beaver are monogamous, and stay with
their mate throughout life.
Habits
Beaver require deep
water for protection from their enemies, and they
alter the landscape a great deal with dam building
and flooding. Dams can be hundreds of feet in
length, and vary in height from only a few feet to 7
or 8 feet, and even higher at times.
Permanent lodges are often
constructed by piling layer after layer of sticks
into a large conical form above the waterline. Two
or more underwater tunnels are then chewed up into
the pile, and an inner chamber hollowed out to serve
as a living quarters. Finally the outside of the
lodge is plastered with mud and rocks, except for
the peak, which is left porous enough to allow an
air exchange to the inner chamber. There are two
levels to the chamber. One level is near the
waterline near the "plunge holes", where the beaver
shed water before climbing to the higher resting or
nesting areas.
In areas prone to flooding, or
where strong currents may be present, beaver usually
construct bank dens by digging tunnels from
underwater up into banks. Bank dens often have two
or more submerged entrances. Many times the beaver
will construct a pile of sticks over the tops of the
underground living chambers. These piles of sticks
are sometimes called "caps".
Shallow pockets are sometimes dug
into banks near the waterline and these are known as
"feed pockets". In northern areas, beaver construct
"feed piles" by submerging large amounts of small
trees and limbs to serve as a food source after ice
prevents the beaver from activity above the ice.
These feed piles are usually constructed close to
the den as a convenience to the kit beaver, who do
not normally travel far from the den itself.
At times, solitary beaver will be
found living alone. These beaver are known as
"bachelors", whether they are male or fernale.
Adult beaver mark out their
territories in early spring by dragging up mud and
debris from the bottom and depositing the debris in
mounds along the shores, where they also deposit oil
from their castor glands. These "castor mounds"
often leave a reddish stain on the bank, and the
odors are powerful enough for a human to easily
detect.
Beaver are very territorial, and
territories seldom overlap. Generations of beaver
may continuously inhabit a choice area, even
building canals to help float food from inland
cutting sites. If and when food supplies are
exhausted, they do relocate to better area. Once
beaver have determined to claim a territory, they
are very difficult to dissuade. If the activities of
the beaver flood roads or damage property, the
beaver usually have to be removed to prevent
reoccurring damages.
Although beaver normally submerge
for 3 or 4 minutes at a time, they are quite capable
of holding their breath for 12 to 15 minutes. They
exhale a little in spurts as they swim or work under
water, and a large beaver is quite capable of
traveling nearly 1/2 mile under the surface before
it must surface for more air.
Migrations of beaver usually
occur with the breaking up of ice in late winter or
early spring as the 22 or 23 months old beaver are
expelled just prior to birthing time for the new
litter. These beaver may chose to go up or
downstream. Although these beaver are capable of
reproducing, they usually do not until the next
season, after a mate and a new territory have been
established. Most new colonies are established
within a few miles of the home colony.
Beaver are primarily vegetarians
although an occasional beaver may eat a dead fish.
Preferred foods include the bark of aspen, willow,
cottonwood, and dogwood, and many other varieties of
trees and shrubs. In early spring, beaver will often
eat bark and twigs of evergreens. In season, beaver
will also eat water lillies, leaves, grassses,
roots, and a variety of crops including corn, wheat,
oats, carrots, potatoes, apples, clovers, and
alfalfa.
General
Beaver usually
alter the habitat a great deal with the building of
dams, and the resulting flooding of lowlands. The
deeper water behind dams creates a better habitat
for muskrats, and a variety of other wildlife
species such as fish and waterfowl. Mink and otter
hunt regularly around beaver dams. These locations
provide suitable denning sites as well for these
furbearers.
Dam building on trout streams can
have an adverse effect on trout survival by slowing
the water and allowing it to warm to temperatures
higher than the trout can tolerate. Dams also serve
as barriers to migrating trout and salmon. At times,
beaver cause significant amount of property damage
by cutting trees, and flooding large areas also
killing the timber. Culvert plugging is common, and
often causes roads to flood and to wash out,
Beaver are also host to an
internal parasite, giardiasis. Water reservoirs
inhabited by beaver can and do become contaminated
by the giardiasis cysts, which are too small to be
filtered out of the drinikng water. These cysts
hatch in the small intestines of people who drink
the contaminated water resulting in diarrhea,
nausea, and stomach aches.
Serious beaver predators include
mountain lions, wolves, lynx and bobcats. At times,
a bear can and will kill mature beaver. Juvenile
beaver are vulnerable to coyotes, eagles, and large
owls as well. Tularemia can be a devastating disease
in beaver, wiping out entire populations when
conditions are good for disease transmissions.
Tularemia infects livers, and is usually fatal to
beaver of all ages.
A beaver is considered to be old
at 12 years of age.
