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Beaver
THE SPECIES: Castor canadensis
Twig in mouth and nimble forefeet busy, a beaver inspects and repairs its dam. As a tree cutter, this largest of North American rodents is unique among mammals. As a dammer of streams, it can alter a landscape while creating its own special home -- the beaver pond. And, as a wearer of fine fur, this New World species is credited with a leading role in the European exploration and settlement of much of Canada, including the Yukon.
DISTRIBUTION
Beaver are found across Canada and the United States except Florida, the arctic tundra, and treeless regions of the Canadian prairies and American southwest.
Here in the Yukon, beaver inhabit forested and subalpine regions throughout the territory. Ideal sites for colonies are ponds, small lakes, and narrow, slow-moving streams. Highest densities occur in burn areas where aspen poplar and willow are abundant. The Takhini and Teslin burns are good examples as is the watershed of the Liard River. In areas such as these, colonies along rivers are separated by an average of 2 km but some colonies may be as little as a few hundred metres apart.
CHARACTERISTICS
More at home in water than on land, the tail-slapping, tree-munching beaver is one of the most easily identified of mammals. Its most characteristic feature is its broad, flat, black tail. Up to half a metre long, it is used not only to warn family members of danger, but also to maneuver in water, to prop up its owner while it gnaws through trunks, and to lever logs being dragged to the pond. The tail is also a fat storage organ and to lose excess heat during exercise.
Although clumsy and hump-backed on land, the beaver is highly adapted for life in water. Its dense, brown fur traps air in a buoyant, insulating layer. Its hind feet are broad and webbed, serving as powerful paddles. Other adaptations to its aquatic lifestyle include lips that close behind front teeth; nostrils and ears that close; and eyes protected by transparent eyelids. These features enable it to eat under water. Beaver are able to stay submerged for up to 15 minutes.
Nature's logger, the beaver chews through wood with stout, ever-growing incisors kept chisel-sharp by the frequent grinding of upper teeth against lower. The power behind those orange teeth comes from a strong skull and massive jaw muscles. Once a tree is down, the beaver's sturdy body, half a metre long and heavy with bone and muscle, is ideal for dragging the branches, or a section of trunk, to the water.
Weighing up to 23 kilograms, Yukon beaver are lightweights compared to Ontario beaver, some of which weigh almost twice as much. Poorer habitat and shorter growing seasons may explain why Yukon beaver are smaller than southern Canadian beaver.
CASTOR'S CONSTRUCTION CO.
By tuning in to the noises made by water flowing over obstructions, beaver get their directions straight for damming. Then they use small, agile forepaws to push mud and stones into a ridge along their chosen site across a narrow stream or even a broad slough. With the whole family chipping in, they push sticks and logs into the muddy ridge for support, sometimes using the peeled remains of winter food caches. Then they add more muck and rock, and keep on building until the dam is high enough and long enough to prevent water from flowing over or around it. Instead, the trapped water seeps slowly through the dam, which acts more like a sieve than a blockade.
A beaver dams size reflects its age and may be more than three metres high and hundreds of metres long. Sometimes a dam spans an entire stream, changing its course. The result is a pond two to three metres deep in which its architects can build a secure lodge and swim beneath the thickest ice.
Dams extend beavers' food-gathering range by flooding cut-over areas and giving access to new stands of shrubs and trees. Higher water levels then kill water-intolerant trees, creating new wetland habitat. Through frequent inspections and maintenance, beaver keep dams in good repair throughout the life of the colony.
Home-builders too, beaver dig burrows in banks or build lodges of sticks and mud; some do a combination of both. 'Bank beaver' live on rivers, where currents sweep away sticks and make lodge-building difficult. 'Lodge beaver' live in quiet waters, where you can find their houses tucked against a shore or completely surrounded by water.
The beaver lodge is typically a mound of logs, sticks, and mud, that rises above water level. The nesting chamber within is covered by a loose roof of sticks to allow for ventilation. An underwater tunnel near the bottom of the lodge gives beaver entry to their dry home and usually prevents entry by all predators except otters. In ice-free times, however, wolves and bears sometimes break through the shell.
The lodge dwellers sleep and dry off on ledges surrounding the tunnel entrance. Water from wet coats filters down through a carpet of wood chips and fibers. Before cold weather sets in, beaver winterize their homes by adding more layers to lodge roofs and smearing them with mud. When frozen solid and covered with snow, the lodges are snug and almost impossible to penetrate.
THE SOCIAL SIDE OF LIFE
Beaver life is a family affair that centres around an adult female. She chooses the colony's home site and, here in the north, mates with one male for life. Her mate and litters of one or more years make up the rest of the family circle. An average colony has five members, and all colonies live within small, well-defined territories that contain their ponds and food supplies.
A beaver family works together to build and repair dams and lodges, and to prepare a winter food cache. When kits are young, all family members bring them leafy branches and herbs to eat. The adult male brings them most of their solid food, an unusual trait among mammals. By the time autumn arrives, kits are ready to take part in the gathering of food for winter.
With all the time and effort spent in the building and maintenance of dams and lodges, beaver have to protect their investments. During spring break-up, when juveniles are on the move in search of sites to set up or take over colonies, an established colony goes on the defense. The whole family piles mounds of plants and mud on shore, then marks them with castoreum an odorous secretion from glands near the anus. These scented sign posts create territory boundaries and let dispersing beaver know the age, sex, and reproductive condition of family members. They not only discourage intruders, but also let dispersing beaver know if a vacancy exists in the area.
Juveniles leave their home colony at one to three years of age. They travel by land and water, sometimes more than 150 kilometres, in search of sites where they can start their own colonies. En route, they often clash with members of established colonies, and many a beaver with a battle-scarred pelt and torn tail has been seen.
Although young beaver are quite safe in their home colonies, about ninety percent of dispersing yearlings and two-year-olds die. Some are killed by predators while others are crushed by moving ice, or die from diseases before they can establish a new colony. A few of those that succeed may reach the ripe old age of twenty years, but most beaver die at less than half that age.
Colony size is often cyclic. Usually, three to four years after a new colony is established, it reaches its greatest size. After five or six years, the beaver may begin to over-eat their food supplies. As supplies diminish, fewer young are produced and fewer beaver survive the winter. Eventually the colony abandons its site to avoid starvation. After a few years, the food supply may regrow to point where new beaver are able to move in.
Some colonies are able to shift their cutting operations up or downstream as food supplies diminish. In this way, thay are able to occupy the same colony site on a semipermanent basis.
GNAWING THROUGH THE SEASONS
While winter winds howl and temperatures plunge, a family of beaver sits tight in its lodge. Beneath the ice, they live in total darkness for up to 8 months of the year, sleeping, eating, and grooming their waterproof fur with split nails on two toes of each hind foot. Having cached branches and logs of willow, poplar, dwarf birch, and aspen near the lodge's entrance, they brave icy pond waters only to visit their pantry. Beaver eat twigs, leaves and buds, or gnaw at soft inner bark. In February and March, adults take to the water for a different reason -- mating.
When the ice melts, juveniles leave their home colonies and the rest of the beaver get busy. They patrol their territories, scent-marking and challenging intruders. They sample the new leaves, twigs, bark, and buds of most plants growing in or near the water. Aspen is the beaver's first choice for food throughout North America but is not always abundant near Yukon waterways. As a result, willow is our beavers' main source of food. They are also fond of water lilies and their roots. They eat spruce only when faced with starvation.
In spring, beaver repair dams threatened by high water. They also build new ones to flood an even larger area and bring more trees and shrubs within easy reach. Later on, when water levels drop, they save energy by digging canals and floating logs to their ponds instead of dragging them.
Early in summer, three or four kits are born within lodges or bank burrows, each weighing roughly half a kilogram. Fully furred and with incisors ready to chew, they can swim in the underwater entrance within a few minutes. They start to eat leaves and herbs within a few days. At two weeks of age, kits make their pond debut and start slapping their tails soon after. Here in the north, beaver grow slowly throughout their first year, and then only in subsequent summers until they reach adult size at four years.
With the first frosts of autumn, beaver step up their logging as they begin to prepare food caches for winter. These gnawing wizards can fell small aspen in three minutes and will cut down trees up to a metre in diameter. They first chew one groove, then add another below and rip out the wood chips between until the tree topples. A logging skill beaver lack is the ability to aim the direction of the fall. Consequently, they are occasionally crushed by their own timbers.
Since beaver on land are vulnerable to predation by coyotes, wolves, foxes, eagles, bears and lynx, they rarely go inland more than thirty metres. And since it takes more time and energy to fell a large tree than a small one, the larger the tree, the closer it must be to the water. Large trunks are left behind while branches and saplings are dragged to the water and piled in a cache near lodge entrances. Beaver cut trees as long as they can break through the ice near shore. They rely on the cold water to keep their winter food supplies fresh.
BEAVER AND PEOPLE
Beaver pelts have historically been among the most desirable of furs. In the old days, Yukon Indians set nets in front of entrances to beaver lodges and used moose-hoof bells to signal a catch. In spring, they also lured beaver to their death by baiting holes in the ice with poplar twigs and branches, then spearing the beaver with antler or bone spearheads.
For the Tlingit and Tagish, the beaver is the most important crest animal or totem. They call it "Smart Man" because of its ability to cut trees and build dams like people do. They also tell powerful legends of an eight-legged, double-tailed beaver that is featured on ceremonial shirts that have been passed on for generations.
During the 1700s and 1800s, felt hats made from beaver fur were the fashion rage in Europe. Demand for beaver pelts lead to the exploration and settlement of large tracts of North American wilderness, with fortunes made or lost, and bitter trapping feuds along the way. By 1840 the beaver was largely exterminated in eastern Canada. As a result, a representative of the Hudson's Bay Company -- Robert Campbell -- ascended the Liard River and entered the Yukon in a search for rich new trapping grounds.
Today, the beaver is Canadas national emblem. Although its fur may not be as valuable as it once was, the beaver is still valued for food and for its role in wetland creation.
VIEWING OPPORTUNITIES
Any spot where aspen or balsam poplar grows near water is prime beaver habitat. River and lake travellers are in the best positions to view beaver, but hikers and highway drivers have a good chance of spotting them as well. You will likely see sign before seeing the beaver themselves. Look for pointed stumps, dome-shaped lodges with nearby underwater branch piles, dams, canals, and trails that beaver use for dragging twigs and branches to their ponds. You may also smell beaver sign if you are near a scent post.
Beaver are most active at night, dawn, and dusk. They swim with only their heads above water, and trail a characteristic "V" wake. They have poor eyesight, but excellent noses and ears, so approach them quietly from downwind. If you hear a resounding SMACK!, you can bet they've spotted you or something else that's a potential threat. Sit tight or back off and try a different approach. They will reappear eventually, and your patience will be rewarded with a viewing of one of nature's most ingenious mammals.