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Out in the Woods With… The Incredible Beaver

November “Beaver” Moon… peak beaver activity time Picture Credit: NASA, GETTY

By Kevin McKeon, Maine Master Naturalist

Within the Hall Environmental Reserve in Springvale sits Deering Pond. Its waters and beaver dams create a vibrant wetland habitat. During a recent beaver survey with a game warden, this writer was told that molesting an active beaver dam or lodge should not be done for various reasons. Only a trained professional can assess both the volume of dam-impounded water and the potential damage from its release downstream. A sudden turbulent water flow, carrying built-up sedimentation, can result in short-term native plant habitat loss, impacting several generations of native species dependent upon those habitats. This includes waterfowl, amphibian, and other animal brood-rearing areas. It can also flood housing and property resulting in costly restitution.

Now, let’s talk beavers! Beavers evolved into today’s form in Germany 10 to 12 million years ago. They spread throughout Asia and crossed the Bering Land Bridge into North America about 7 million years ago. Living for 10-12 years in the wild and 30 years in captivity, beavers are 3-4 feet long (tail included), and 40-60 pounds. They’re the second largest rodent living—smaller only than the 50-pound South American capybara. Once among the most widely distributed mammals in North America, unregulated trapping, fed by the insatiable demand for felt hats, eliminated them from much of their range by the late 1800s.

Why use beaver fur for felt? Beaver fur is thick, with about 100,000 hairs per square inch, the amount on an average thick-haired human head! It consists of coarse, outer guard hairs, and a rich, woolen, oily, heavily barbed fur underneath. It’s this underfur that’s prized by both the beaver and the felt makers. For the beaver, the combination of thickness, being barbed to maintain a thick cohesive matrix, and infused with body oil, combine to keep the beaver’s skin dry—in the water!

These qualities have made for the best felt for hat-making. Read about it (and how Mad Hatter came to be!) here: Over time, changing fashions along with beaver management policies have allowed for re-establishment in much of their former range.

The beaver’s incisors (front teeth) are harder and yellow on the front surface than on the back due to the iron content. The lower incisors rub against the inside of the softer upper incisors, so the back wears faster creating very sharp, chiseled edges that enable a beaver to easily cut through wood. These teeth grow continually, getting worn down by cutting trees, peeling bark and feeding. Beavers are also territorial, protecting their area from other beavers when needed. Teeth marks, caused by territorial combat, are sometimes found on trapped and dead beavers. But often, lodges are shared with muskrat, mink, and otters!

Beaver tails have many uses. Covered with leathery scales and sparse, coarse hairs, their tail slaps loudly against the water to frighten predators and warn other beavers. It stores fat for energy and releases body heat to help control body temperature. On land, the tail helps with sitting or standing and serves as a counterbalance and support when a beaver is walking on its hind legs while carrying building materials with its teeth, arms and hands. Their hands are adept at grasping and manipulating objects and are used during eating and dam and lodge building. In tree-sparse areas, beavers use rocks for their dams, plugging the gaps with mud.

Beavers have a clear, inner (nictitating) eyelid, providing eye-protection while allowing good underwater eyesight. Their larger webbed feet propel them at 5 mph underwater, with their tail acting as a rudder for steering. At times, a beaver will remain underwater for 5 or 6 minutes, but usually limit their dives to about 30 seconds. 15-minute dives are possible, redirecting blood flow to their brains and lowering their heart rate in half!

Beavers live along rivers and streams and in ponds and lakes…almost anywhere where adequate year-round water flow exists. They’ll often dig and build their lodges along the banks. In other areas with adequate vegetation, they’ll create ponds by building dams across streams. They’re the only species, other than humans, that can both create its own habitat and alter the environment. The wonders of the habitats created by this Keystone Species will be the subject of a future piece.

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