Beavers are skilled lumberjacks
Near a large marsh in northwestern Minnesota, I recently stumbled upon a small, yet significant aspen clear-cut. Over the years I have often explored this area while hunting for ruffed grouse or deer. With its abundant quaking aspen trees, a few scattered bur oaks, hazel, cranberry, alder and willow, the wooded highland provides outstanding habitat for many species of wildlife, not just grouse and deer.
It had been a year since I last visited the area and, much to my astonishment, I scarcely recognized part of it. Large diameter aspen trees had been cut down and were scattered about like matchsticks on the forest floor. Some trees were leaning against neighboring trees, unable to complete their fall.
Other trees, which had been grounded and subsequently cut into manageable lengths, were known only to exist by the numerous, conspicuous and aromatic piles of wood chips spaced at three-or-so-foot evenly spaced intervals. And stumps, resembling freshly sharpened heads of giant pencils protruding out of the ground, were virtually everywhere. Well-worn skid trails leading to the marsh marked the paths that the pole timber and branches, one length at a time, were hauled over.
Indeed, skilled lumberjacks, descending upon the woodland in the middle of the night - multiple nights, really - had laid claim to the chalky, slick-barked stand of popple trees. Only a major freeze-up, deep snows and cold would prevent them from finishing the job of felling the remaining standing trees. It is, after all, the way of the beaver, who as sawyer and engineer is one of only a few species of animals with the ability to change their environment in order to suit their own needs.
The beaver is the largest rodent in North America. Adults average 35 pounds, with some individuals reaching as much as 65 pounds. Specimens of 90 pounds have also been found. Beavers can reach four to five feet in length from the nose to the tip of the tail. Prehistoric beavers were almost as large as today's bears. Imagine the dams and lodges animals of that size would have constructed. One can easily imagine lakes, not ponds, being created by such creatures.
Long-lived for rodents, beavers can reach 20 years of age. They tend to mate for life. Kits remain with their parents for two years until they disperse to locate their own mates and territories. One litter per year of two to four kits is born to a mated pair. So many marvelous adaptations help to make the beaver perfectly suited to an aquatic lifestyle. Powerful hind legs with flipper-like webbed feet propel them through the water with ease. Nostrils can be closed to keep water out. And clawed toes help assist digging and gripping sticks.
Beavers have extremely dense fur that repels water and keeps them warm in frigid conditions. Their massive chisel-like incisors imbedded in equally massive skulls, where powerful muscles attach to supporting jaws, provide beavers with the necessary means to cut through wood. And their broad and flat tail, which is used as both a rudder for swimming and for support when standing, is also used as a warning signal. A loud slap on the surface of the water warns other beavers in the pond that danger lurks nearby.
Aside from the impressive dams that beaver construct to hold the water they require to survive, the lodges, too, are unique and elaborate in design. The inside chamber may be as wide as eight feet and as high as three feet and is lined with soft vegetative materials like grass and woodchips. Depending also in the structure's design, the entrances may differ as well. Some entrances are bored vertically through the floor of the lodge, whereas other lodges are entered through gradually sloped entrance holes.
Like the colony of beavers that I encountered near the big marsh, beavers are especially active in the fall as they prepare for winter. Branches and sections of felled trees are transported near their lodge where they are stored underwater. Called food rafts, beavers cache these sub-surface food items for consuming throughout the winter months. When a meal is needed, the beaver simply exits the lodge, swims below the ice to the food raft, and carries back with them something to eat inside the warm and cozy lodge. It is the nutritious bark of the aspen tree that is among their favorite foods.
Though sometimes viewed as pests because of the problems they can create for people, beaver ponds provide many benefits for other species of wildlife. Flooded trees often die and subsequently become excellent cavity trees for wood ducks. River otter, mink, turtles, amphibians, aquatic invertebrates, fish and many species of birds, such as belted kingfishers, great blue herons and scores of songbirds, shorebirds and waterfowl, use beaver ponds and their associated habitats. In time, because of sedimentation, diminishing timber or hydrologic changes, beavers eventually abandon their ponds. These old ponds often become lush meadows.
How and why these extraordinary animals do what they do is one of the many mysteries in the animal kingdom. Researchers, for example, believe it's the sound of running water that compels beavers to construct their dams. Regardless of their motives, the beaver, with all its amazing engineering feats and contributions to the environment and other species of wildlife, provides us with a multitude of reasons to get out and enjoy the great outdoors.
Blane Klemek is the Bemidji area assistant wildlife manager, DNR Division of Fish & Wildlife. He can be reached at firstname.lastname@example.org.