Beavering On!

At a snail’s pace, I belly crawled down the bank toward the beaver pond. Pushing the fresh aspen branch in front of me, I screened my approach as much as possible. The big male eyed me from the water, clearly uncertain how to respond to this unusual visit. Nearly breathless with anticipation, I felt some of the uncertainty. Never would I have dreamed of being this close to a beaver without him slapping his tail on the water and diving, but it was unclear whether he would accept the branch. It was an encounter I will not forget.

The place was Utah, deep in the mountains where we were camped for a week of elk hunting. Having filled my tag on opening day, I spent the morning improving our camp and getting organized for dinner while the others were hunting, then decided to take a walk. I soon came upon a small beaver pond, and as I slowly raised my eyes over the dam I saw a pair of beavers busily wedging aspen branches in the mud for their winter food cache.

The female soon spotted me and dove with a slap of her tail, but the larger male chose to back away to
the far side of the pond so he could gauge the threat. The female resurfaced in a few minutes and
swam in circles, murmuring quietly to her mate, probably looking for reassurance. Gradually they
seemed to understand I meant them no harm, so I was able to rest there quietly for three hours that
first day watching them work. On the second day, I took the opportunity to offer the aspen branch at
close range and was stunned when the male finally swam over and pulled my offering into the water.

It’s unlikely that I will ever have a similar experience with these amazing animals, but the event served
to further reinforce the great respect I had for the industrious beaver. It is no exaggeration to state that
beavers played a huge role in the exploration and settling of the US, and were nearly eliminated in the
process. It is also true that the beaver is one of the most influential animals in nature, with the ability to
change landscapes and to improve wildlife habitat in a way that no creature other than man is able to
accomplish. Hopefully you will agree with this assessment as you learn more about them.

There are fossil records going back seven million years to document the amazing longevity of the North
American beaver. It is known scientifically as Castor Canadensis, being first catalogued by early
explorers in Canada who learned about the beaver from their Native American guides. The genus name
castor refers to large scent glands located at the base of the beaver’s tail that produce an oily substance
called castoreum which the beaver uses to waterproof its fur, and for scent marking. The animal is
almost universally called a beaver, even though there is another, much smaller rodent living in the
western Cascade and Olympic Mountain ranges called the mountain beaver (Aplodontia rufa). Since the
two are only distant relatives, I will use the short hand name for the animal we know here in Maine.

Our beavers are the largest rodents in North America, and second in the world to the South American
capybara. Adult beavers average around forty five pounds, but very old specimens have been recorded
up to one hundred and ten pounds. They run up to three feet in length plus a tail that can exceed
twelve inches. The beaver is semiaquatic, capable of walking and working on land, but far more adept in
the water where it has few equals. With large webbed hind feet and a powerful paddle-shaped tail, the
beaver has been clocked at underwater speeds up to thirty four miles per hour. His ears and nose close
when he dives under water and a special membrane covers the eyes to allow vision. If he chooses, an

adult beaver can slow his heart rate to remain submerged up to fifteen minutes, quite handy if he is
performing underwater chores or swimming from danger. Those four large front teeth, incisors,
continue to grow throughout their lives and are self-sharpening for efficient cutting of wood. When
threatened, beavers will make hissing or growling noises, and may lunge forward with those razor shape
teeth.

In rivers or existing ponds or lakes with sufficient water, beavers will dig dens along the shoreline,
generally adding a pile of logs and sticks to protect the entrances. But we are most familiar with beavers
and their amazing ability to build lodges and the dams that create their own secure ponds. The need for
these dams is to have enough water depth so that even the coldest winter weather cannot freeze the
pond to the bottom. If the beaver miscalculates in building the dam, or the water level falls in
midwinter for any reason, the beavers may perish.

A beaver lodge begins life as a pile of tree limbs, often using a stump or downed tree as a base. By
gradually adding more limbs woven together on top, further secured with weeds, stones and mud, while
leaving an air hole near the top, the beaver creates a home with one or two underwater entrances.
Inside will be one or two warm and secure chambers above the water level that allows the beavers to
rest and to care for newborns. A family group might contain three or four adults and several juveniles.
Most predators are unable to attack the beavers, thanks to hard mud on the roof of their lodge, along
with snow and ice in winter. Sometimes large bears manage to break through, killing the beavers or
forcing them into the water with no refuge.

The dam is critical for holding back moving water, either a slow moving slough or a stream with a
modest pitch. The beaver uses her mouth and small, clawed front feet to move sticks, rocks and mud
into place, making an amazing number of journeys back and forth in the process. As the water begins to
accumulate behind the dam, the beavers will add new material to raise the water level. They are highly
attuned to the sound of running water, and any break in the dam will trigger an immediate repair
mission. In a test of this trait, scientists placed a tape recorder in a field near a beaver pond, playing the
sounds of a stream. Despite the recorder being on dry ground, the beavers covered it with branches
and mud.

It is common for beavers to exhaust the food supply around their dam and then move to a new location,
sometimes walking miles in a dangerous pilgrimage. If there is sufficient food available, beavers will
gradually widen and raise a dam in suitable locations, flooding more and more land upstream, and
making it easier to reach new trees. In other sites, they simply build additional dams up and
downstream of the main pond. Many years ago on a jet over northern Canada, I spotted a large dam
and lake below me, guessing its length at several hundred yards. In 2007, scientists spotted a dam on
satellite photographs of Northern Alberta that measured nearly one thousand yards long, twice as long
as the Hoover Dam. Of course this dam building can bring beavers into conflict with humans, and while
the beavers generally lose such battles, they don’t give up easily.

Nighttime is the period of most activity for beavers, providing them safety from some winged predators
like bald eagles. Their eyesight is rather weak, but they have superb hearing and sense of smell to
detect danger. When on land, beavers are slow and ungainly, but they are often forced to emerge to
gnaw through the trunks of trees to fell them, hopefully close to or in the water. Around their ponds,
beavers excavate channels that allow them to swim into shallow water, to float building materials, and
to provide escape routes if they are attacked by coyotes, wolves, lynx, bobcats, mountain lions or bears.

While beavers are amazingly skilled at cutting down even large diameter trees with only their large front
teeth, it is hazardous work, and I have seen photos of beaver skulls lodged in fallen trees.
Beavers live almost exclusively on a diet of twigs, inner bark, new shoots and leaves of their favored
trees. While their digestive systems are evolved to convert all the essential nutrients from only the
aspen tree, beavers will also feed upon softwoods like alder, willow, birch and pine or hardwoods like
ash, beech, maple and black cherry. In the spring, they will feed upon sedges, water lilies and cattails.
They prefer new growth as opposed to mature trees, and in the autumn, beavers will create large piles
of branches stuck in the mud around their lodge to guarantee winter food supplies with minimal
expenditure of energy.

A female matures at three years and has a short estrous period of a day or less, with mating often done
in their winter dens between December and April. Unlike most rodents, beavers will remain with a mate
for many years, both of them involved in raising a family. Gestation occurs over four months, with two
to six kits born. The young beavers may live with their parents up to two years, learning the skills
needed to survive on their own, before they are pushed out of the family group to find a new territory.
In areas with adequate water and food supplies, beavers have been known to live up to twenty years.

To survive in a harsh climate the beaver is protected by a heavy pelt covered in long, brown outer hairs
and a dense layer of fine inner hair, with thick layers of fat underneath. That dark, lustrous pelt is what
drew so many European adventurers and trappers to push deep into the interior of North America. The
hides were in great demand in England, used to make hats and other clothes, while the castoreum has
long been used in perfumes and food additives. Native Americans had long harvested small numbers of
beaver for food and hides, but the white trappers knew no restraint, only the lure of gold and silver.
Tens of thousands of eastern beaver pelts were sold to buyers each year in the 1600’s and 1700’s.

The trappers took great risks pushing further and further into an untamed wilderness, and suffered all
manner of hardships to collect large bundles of beaver pelts for trading or selling to buyers like the
Hudson Bay Company. As beaver numbers dropped in the eastern US and Canada, the trappers kept
moving further west until they reached California in the early 1800’s. While the trappers led the
opening of the west to further settlement, by the 1840’s beavers were nearly eliminated from their vast
former range. Fortunately the population has rebounded to an estimated fifteen million today, far
below the estimated original population of one hundred to two hundred million. Beavers are
considered fur bearers, and as such, there are legal restrictions and open seasons for harvesting them.
With fur coats having fallen out of favor, there is far less trapping of beavers today. The most recent
Maine statistics I found showed fewer than one thousand active trappers of any species in the state, and
twelve thousand six hundred beavers tagged in 2015. Nuisance beavers may only be removed with
permission of the Department of Inland Fisheries & Wildlife.

Earlier I mentioned the vital role that beavers play in our natural world. Many scientific studies have
documented the long term impact that beaver dams and ponds can have on flora and fauna around
them. The extensive cutting of trees by beavers creates new openings in thick forests, allowing more
sunlight to penetrate and triggering regeneration. Beaver dams play a major role in controlling the flow
of rivers in arid regions, slowly releasing water over time and allowing streams to maintain more flow
during the summer months, sustaining groundwater levels along with fish and other creatures that
otherwise would die. The dams collect sediment and sequester pollutants that may break down while
resting on the floor of the pond.

Beaver ponds are major holding waters for waterfowl and valued fish like trout and salmon. A study of
Wyoming waterways showed that rivers with beaver activity held up to seventy five times more ducks
and geese than rivers without beavers. The grasses, forbs and shrubs that flourish around beaver ponds
are perfect habitat for waterfowl breeding, and for the insects that provide nourishment. Standing dead
snags in beaver ponds provide excellent nesting habitat for woodpeckers. The cavities hammered out
by the woodpeckers then become homes for wood ducks, flickers, and owls. Herons, kingfishers and
bitterns work the beaver ponds in their search for small fish and crustaceans. Populations of brook
trout, rainbows and salmon also benefit from beaver activity, both because of improved flows of clean
water, and the deep holding water behind the dams while the fish are migrating or holding over the
winter.

While beavers may cause trouble in settled areas when they block drainage culverts and flood highways,
our environment is far better off with a healthy population. The cumulative beneficial impact of beavers
upon river systems is such that states like Utah are actively reestablishing beavers in dozens of new
streams every year. In the state of Washington, studies have shown that beaver dams in the upper
reaches of the state’s major rivers can have a significant impact on holding billions of gallons of spring
run-off and flood waters from major rainstorms, reducing the need for hugely expensive concrete dams
with all of the ecological damage they can cause.

If you have the opportunity to spend some time watching beavers and the wildlife around their homes, I
hope you will do so. They are quiet, retiring creatures by nature, but they are very diligent in caring for
their dams and lodges, thus the term “busy as a beaver.” Once valued mostly for their luxuriant pelt,
there are many other reasons to protect these unique animals. This species has long had an outsized
impact upon our country, and our environment. Long live the beavers!

If you like Ed Robinson’s writing, check out his two Nature Notes books! Click here for more information.