North
American beaver
Castor canadensis
Once abundant beyond measure, it was the beaver and its valuable fur—used to make top hats in Europe—that first attracted explorers to the American West. Then, in just a few decades, this largest of North American rodents was trapped so heavily it nearly disappeared. Over the past century, however, this great engineer of the wilds has made a remarkable comeback.
APPEARANCE
Beavers are nocturnal, so the best way to spot one is to check creeks and
streams for dams or lodges, and then wait there until dusk. Look for a
dark brown animal 35 to 46 inches long (which includes its 16-inch flat,
scaly tail) and weighing 35 to 75 pounds. The beaver’s massive head
has small ears, beady little eyes, and four large, orange incisors. The
front feet contain five widely splayed toes. The hind feet are twice as
long and have webbing between the toes.
SOUND
Beavers hiss at muskrats, strange beavers, or anything else thought to be
a threat. The young whine, much like human babies. Another sound is the
loud, wet slap of the animal’s tail when it is agitated and plunges
underwater. The report scares in-truders and warns other beavers of danger.
FOOD
Beavers eat trees, grasses, forbs, and aquatic vegetation. The soft inner
bark of quaking aspen, willow, or cottonwood is a favorite. A beaver will
hold a branch in its front feet and turn it while gnawing the bark off,
just like we eat corn on the cob. Branches of willows and other trees are
cut and stored underwater in a cache to be eaten during the winter months.
REPRODUCTION
In January or February of its third year, a beaver finds a lifelong partner
and then mates. Three or four kits, born in May or June and weighing about
1 pound, greet the world with fur, teeth, and open eyes.
Kits become skilled swimmers within a week, begin to gnaw wood after just 11 days, and help gather tree limbs for lodge construction within three months. They stay home for two years, helping with chores such as dam repair or, by the second summer, grooming new kits. Their parents send them away during their third summer.
LODGING
Dome-shaped beaver lodges may be either freestanding or attached to a bank.
Beavers live inside these sturdy homes safe from predators such as coyotes
and wolves. To prevent predators from entering, beavers build lodge entrances
below water level. Using sticks and mud, beavers build dams on streams
and rivers to raise the water level so it remains above the lodge entrance
and to create a deep pool for storing food.
ADAPTATIONS
A beaver has an extremely sharp sense of smell, which compensates for its
relatively poor sight and hearing. Beavers use smell to detect predators,
recognize relatives, and determine which branch will be the tastiest.
A beaver can see underwater thanks to its clear eyelids. Valves in the nostrils and ears keep water out. Fur-lined lips behind the teeth seal the mouth when a beaver swims while carrying a branch in its teeth.
Beaver incisors grow continuously, and gnawing wood keeps them worn down. A beaver can cut down a 5-inch willow in just a few minutes.
Using its webbed hind feet for propulsion and its flat tail as a rudder, a beaver can swim up to 6 miles an hour. It can also hold its breath underwater for up to 15 minutes, helping it to avoid predators.
Beavers are active year-round and must conserve heat in the frigid waters
of winter.
A thick layer of insulating fat is covered by short but dense underfur. The
wooly underfur is covered with long, course guard hairs the beaver preens
with water-repellent oil it combs from anal glands with its paws.
STATUS IN MONTANA
The industriousness that makes beavers so fascinating can also make them
pests. Beavers cut down beloved trees, and their dams cause flooding and
plug up irrigation ditches. According to Brian Giddings, Montana FWP furbearer
coordinator, beaver numbers have been increasing statewide over the past
decade due to a decline in harvest resulting from low pelt prices. The
state has recently lengthened the beaver trapping season in parts of Montana
to reduce beaver damage around farms, ranches, and the growing number of
streamside homes.
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