Busy rodents make their mark
Dam Beavers
The building skills of beavers are amazing—and no secret. In fact, in July of 1997, near Grand Rapids, Mich., the handiwork of one beaver family was so impressive that it prompted that city’s Department of Environmental Quality to send a letter scolding a property owner about the “construction and maintenance of two wood debris dams across the outlet stream of Spring Pond.” Citing a raft of laws the dam violated and the lack of a permit for such “activity,” the department enjoined the owner to “restore the stream to a free-flow condition by removing all wood and brush ….”
The response from Stephen L. Tvedten became an Internet sensation, so much so that myth debunker Snopes.com vetted the exchange—and found it authentic. “I would like to challenge you,” Tvedten wrote, “to attempt to emulate their dam project any dam time and/or any dam place you choose. I believe I can safely state that there is no dam way you could ever match their dam skills, their dam resourcefulness, their dam ingenuity, their dam persistence, their dam determination and/or their dam work ethic.”
Combine those admirable qualities with the physical characteristics of Castor canadensis, the largest North American rodent, and you’ve got a formidable crafts-critter. First, those teeth: A beaver’s incisors grow throughout its life, and gnawing keeps them sharpened and their length in check. The front feet are strong, clawed and as effective as hands for holding twigs and digging. Large hind feet are webbed, for swimming. This fantastic swimmer (up to 4mph, submerging for half-a-mile or 15 minutes) also has built-in earplugs, nose plugs and goggles: Handy musculature closes off ears and nose, and membranes protect eyes. The broad, flat tail acts as a rudder, kickstand and warning device (slapping the water or ground). The animal’s wonderfully dense fur—so lush that the American fur trade almost extirpated them by the early 19th century—is made water-repellent by an oily substance from a gland under its tail. All in all, quite the design.
And they’re quite the designers. Beavers don’t build dams just for fun; starting in late summer, they work to create the environment in which they will build their lodge, store their food and live for a few years. Their canvas is usually a gently flowing stream or pond boasting an abundant food supply (bark, roots, leaves, aquatic vegetation). The dam’s main purpose is to slow the flow of water and raise it to at least two to three feet deep, allowing for underwater entry to the lodge, safe from wolves, bears and other predators. The dome-shaped structure, with one or more chambers, may be built against a bank or out in a pond and is well insulated with mud, leaves, twigs and gravel. As winter approaches, beavers poke stripped sticks and branches into the mud outside the entrances so that, if their pond freezes over, they can nip out underwater and grab woody snacks they’ve cached right outside.
The whole colony, comprising the monogamous parents, the current litter of kits and year-old kits, shares the effort. Females seem to do most of the heavy lifting, whereas males inspect. (Speaking of “dam work ethic”—the longest recorded dams top 2,000 feet long.) Once their work is complete, beavers fatten up for the winter, collect food for the cache and maintain lodge and dam. When their acute hearing picks up the sound of running water, strong instincts send them searching for holes to plug.
Through their efforts, beavers also revamp local ecosystems, causing nutrients to proliferate in the water, which draws fish, birds and other wildlife that will stay long after them. But, of course, these “new and improved” habitats can vex human neighbors. Roads may get washed out. Ornamental trees may become building materials. Agricultural land can get swamped. Correspondence from government agencies may appear in mailboxes.
The Virginia Cooperative Extension lists a variety of measures for dealing with troublesome beaver activity. They include deterrence (cutting vegetation around and near water), repellents (bitter-tasting Ro-Pel), fencing and water-leveling devices (the aid of a hydraulic engineer is suggested for the latter) and, as a last resort, a shotgun (with permission from the requisite authorities). The method at the top of VCE’s list, however, is tolerance. After all, beavers are “intriguing … fun and educational.” The Grand Rapids DEQ dam sure got schooled.
