LIVING WITH BEAVERS - A TALE OF A TAIL
Here’s the paradox about the North American Beaver: It’s a Canadian icon and a symbol of industrious energy. A humble, communal, family-oriented creature, it’s a survivor of everything our weather can deal out. You unflinchingly admire them – and then they set up house in your yard.
A beaver can chew through a 12-cm wide tree trunk in 30 minutes. It can lop a tree into lengths overnight to be carted away for breakfast. If you have damp, low-lying property near your trees, this animal – the world’s second-largest rodent – may dig out its own channel to swim closer to the trees. I know this for fact.
On my own property, it looked as though they had hired a small excavator to neatly pile banks of mud along the creek they had dredged to get to the tag alders and willows in our wetland. It didn’t take long before the perimeter of the wetland was peppered with telltale white cones of wood atop the stubs of harvested trees. A stockpile of downed branches grew by the creek. We fretted over whether they’d dam up the wetland and flood our basement. It’s a familiar concern.
“We used to talk to people about beaver problems a lot,” says Jan McDonnell. The retired biologist with the then-Ministry of Natural Resources was for many years the go-to person for answers about wildlife. They’re a challenging animal to deal with when they start encroaching on private land or threatening roads.
“People would want to have the beaver live trapped and think it can be taken miles away,” says McDonnell. “But relocated beavers tend to fare very poorly.” For municipalities, she adds, there are continuous concerns when beaver dams threaten roads. Even if the odds of flooding are remote, the liability fears push them to rid the waterway of the beavers.
As much as we may think we know about beavers, their physiology and lifestyle have sparked curiosity and misinformation for generations.
Castoreum, the secretion from a pair of glands at the base of the beaver’s tail, has verified uses. The glands have been collected for centuries as an additive in perfumes. It’s still happening today: Some accounts describe the oil as adding a leathery musk or fruity middle note to perfumes. It has also been used to enhance flavour in foods, notably at one time in ice cream. It’s a rather expensive and unsavoury process that has fallen from use. Few merchants want to boast that the oil from glands beside a beaver’s anus enhances their French vanilla scoop.
The oil also has sparked centuries of other claims about its miraculous powers. There are tales that the oil was an aphrodisiac. The dried, pulverized gland could reduce fever when combined with wine; the oil could cure epilepsy, strengthen the brain, and either cure sleeplessness or prevent sleep depending on the salesman.
There is one proven medical value in the oil. Beavers eat a lot of willow, and the green fresh layers under the bark of willow contain salicylic acid, the same stuff that’s in aspirin. So tales that it could cure earache or tooth ache are potentially true.
The beaver, when allowed to keep its glands, uses the oil for two purposes. It’s combined with urine to mark its territory. The oil is also excellent water repellent, and keeps the outer layer of a beaver’s fur virtually waterproof. The animal spends much of its time coaxing castoreum from its glands and grooming it into its fur.
That glossy outer layer of fur protects an undercoat of wool that inspired the rapacious trapping of beavers from the 1600s on. Felt is one of the world’s oldest textiles but when Europeans discovered the qualities of felted wool from beaver, it sparked an economic frenzy. The value of beaver fur was arguably the most significant reason behind the European settlement of Canada.
The Hudson’s Bay Company, granted a charter to explore and sell furs in 1670, “owned” and governed almost half the land of this country, and a chunk of the U.S., until deeding it over to Canada two years after Confederation. By 1930, the market for furs had all but wiped the species off the map of North America. Conservation efforts and changing tastes in fashion have allowed the beaver to re-establish itself across the continent.
And the landscape has changed as a result. Beavers, or Castor canadensis, are considered the only mammal other than humans capable of such significant manipulation of their environment. Far from being destructive, the engineering work beavers conduct is a trigger for biodiversity. A beaver pond becomes a new home to hundreds of species of aquatic life, becoming food for moose, nesting habitat for red-winged blackbirds, herons, rails, warblers and sparrows, and home for otters, moles, weasels and muskrat.
Once the beavers have exhausted the supply of poplars, birch, alders and willow around the pond, they’ll add to the dam, head farther upstream or move elsewhere altogether. The pond left behind continues to grow over, developing meadow vegetation that eventually takes over to supply habitat and food for deer, rabbits, mice and many other forms of wildlife.
But, why a pond? Why are they driven to dam up waterways?
The answer lies in a unique evolution over thousands of years. We can be thankful the ice-age beaver is no longer around since it weighed in at more than 130 kilograms. Today’s beaver, at a portly 27 kilograms, is not fleet of foot and over ground, it is easy prey. It’s also apparently delicious. Indigenous cultures regarded the beaver as a symbol of wisdom. The tail is considered a delicacy. Its only defence is to take to the water, where its specialized metabolism allows it to stay underwater for up to 25 minutes.
Webbed hind feet can propel the beaver at surprising speed; the flat tail performs as a rudder — and a slap on the water serves as warning to the entire family. Its nostrils and ears can close up while submerged. A special clear eyelid allows it to see underwater. They have extra lips behind their front teeth, so they can carry food underwater without opening their mouths. With all those adaptations, a dam is just the trick to bring water closer to the trees and safe access to dinner.
Scientists have been scratching their heads over the beaver’s ability to subsist almost solely on wood through the winter. There is an advantage to eating wood, in that there’s an ample supply of it around. Few other mammals are capable of eating it, so there’s little competition for the food. Their front incisor teeth have hard enamel on the front and a softer dentine behind, and they never stop growing. As the beaver dines, the backs of the teeth wear faster than the front, effectively sharpening every time it eats. But wood is not ideal food.
Early dissections found an odd gland attached to a beaver’s stomach. But tests since then have shown it doesn’t secrete anything that can break cellulose down. The researchers conclude that the beaver’s intestines contain bacteria that can ferment the wood, converting it into food energy — a wood beer brewing in a beaver’s guts.
Given that a beaver’s lodge is made of sticks and mud, it’s sometimes thought that the lodge holds the winter’s supply of food. In fact, the actual stockpile of green sticks is kept nearby, under the ice where the animal is safe from predators.
The lodge itself is a brilliant design, either located on the bank of a pond, an island or the shore of a lake or river. It is partially situated on land, with an overhang into the water, where the outer wall reaches from the bottom of the waterbody to the surface. You may have seen odd heaps of mud and grass along the shoreline of creeks; these could be building material for lodge construction. The combination of mudpack and sticks creates a good barrier against the elements, but at the top of the lodge’s dome there is just a weave of sticks to allow ventilation.
Inside, the lodge will be about 2.5 metres across and with up to a metre of headroom. There are usually two entrances, both underwater. They open up to a set of shelves above the waterline, one area for feeding and the other for the family to rest. It’s kept tidy with a layer of grass, wood chips and bark.
Inside the lodge, a beaver pair – they are monogamous — will mate between January and March. As many as five young will be born about three months later, weighing about half a kilogram. The female will curl her tail inward to form a kind of welcome mat for the young. They’re miniature versions of their parents, born with open eyes, a complete coat of fur and fully formed teeth and capable of swimming within a day. Given that fact about the teeth, mother beaver is likely relieved that the young are weaned in just a month.
The young will stay with their parents for two full years, joined by a new litter the next spring. In larger lodges there could be several families living together. But at the end of two years, the elder siblings will get the boot; they’ll have to fend for themselves and search for a new home. They may trek as far as 30 kilometres to strike out on their own. In the next year the solitary beaver will reach sexual maturity and begin the search for a mate and a new family. The family cycle will repeat itself for a beaver’s eight to 12-year lifespan.
Although the research doesn’t say much about it, there are many people who refer to “bank beavers.” It’s felt these beavers simply tunnel into the banks of rivers or streams rather than build lodges.
Bill Dickinson, who has studied a series of dams and lodges at the Muskoka Conservancy’s Upjohn Reserve, feels this may be a strictly summer habit. Records of beavers farther south in the U.S. indicate there may be beavers that reside in river banks year-round but in our harsher winters, it makes sense that a lodge would be a more preferable home.
Can people co-exist with beavers? It takes effort. Many years ago, Bruce Lake Marsh was the focus of a hot debate between residents on Bruce Lake on one side of Peninsula Road, and people who defended the rights of beavers to live in the wetland across the road. People on the lake felt their water quality was suffering from the dammed up marsh water. It was a standoff Jan McDonnell recalls could not be resolved.
“Our philosophy was, you figure out what you want and we will make it happen. But they never could.”
It doesn’t always end badly. More recently, the Town of Bracebridge has been challenged by the beavers that have made Henry Marsh home. Developers that own the adjacent land wanted the beavers gone; their dam was not only flooding their property, but sections of the national Great Trail. Local naturalists defend the marsh, considering it to be a sanctuary for a variety of scarce birds. In a deal with the property owner, the Town set up an elaborate system of beaver baffles (formally, Clemson Pond Levellers) – underwater pipes that direct excess water out of the pond without causing the running water noise that drives beavers to build new dam. The beaver pond is stabilized and for the time being the marsh thrives.
We can do the same at a smaller scale on our own properties. Muskoka Watershed Council’s Steward’s Guide series contains a fact sheet on managing beavers on private land. Galvanized wire fencing wrapped around tree trunks is one easy solution to protect your favourite trees. Culverts can be protected with fencing of a special design. Beavers avoid conifers such as pine, spruce or hemlock. If you plant those, they won’t be chewed. There are more tips in the guide, which you can find at www.muskokawatershed.org; search for “living with beavers.”