Thursday, December 04, 2008

Beavers in the Prairie State

Beavers in the Prairie State

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On a recent walk at River Bend Forest Preserve someone I met on the trail asked if I knew a good place in Illinois to see beavers. After a moment’s thought I answered, “Anywhere,” because there are unmistakable signs of them in so many places. Beaver-chewed trees, sticks stripped of bark and the slides beavers create by dragging branches down the bank are just part of the landscape along many bodies of water in the Prairie State. [Photo: Chewed trees, like this oak on the bank of the Sangamon River at Lodge Park in Piatt County, are an unmistakable sign of beaver activity.]

Looking back, though, I realized that my quick answer didn’t really get the questioner any closer to laying eyes on Illinois’ largest rodent. That’s because even though beavers live throughout the state, they are not often seen, since they are most active at night, or near dusk and dawn. My answer really should have been to say that if you want to see beavers your best bet is to find a site on a stream or pond where they’ve been active and quietly watch it in the hour before sunset.

There was a time in the not-too-distant past when it was difficult to find beavers in Illinois at all, since prior to 1900 they were nearly extirpated from the state by unregulated trapping. They bounced back over the course of the twentieth century through a combination of protection and reintroduction, and are now common where suitable habitat exists. Indeed, today, beavers sometimes prove a significant nuisance when their ideas about suitable locations for ponds conflict with ours.

Of course, some humans admire the ingenious ways beavers modify their environment, and their ability to do this also benefits the many plants and animals that make use of wetlands. For beavers, the point of building dams is to create ponds that are deep enough not to freeze solid in winter. This allows them to construct lodges that are accessible only through underwater passages. The typical beaver lodge is a dome-shaped mound made of sticks, logs and mud, and a really big one may be 10 feet tall and 30 feet around. But many perfectly respectable beavers live in burrows excavated in the banks of bodies of water, too. That’s why you may find all of the other evidence that beavers inhabit a pond or stretch of river without ever seeing a lodge. Bank burrows, like lodges, provide beavers with protection from weather and predators.

Beavers possess an array of physical adaptations that suit them for a semi-aquatic life. They propel themselves through the water with webbed hind feet, using their signature, paddle-shaped tail as a rudder. Their eyes are protected by a clear, third eyelid, and their nostrils and ears can be closed when they submerge. A beaver may remain underwater for as long as 15 minutes at a stretch.

Unlike most other mammals, beavers are monogamous, and male and female beaver mates remain together until one of the pair dies. Beaver young live with their parents for nearly two years, so family groups include adults, yearlings and kits together.

If you would like to learn more about beavers or any of the other 59 species of wild mammals that occur regularly in Illinois, I would encourage you to pick up a copy of the Field Manual of Illinois Mammals published this year by the Illinois Natural History Survey. The manual contains all of the information you could ask for in such a book, but it is written with attention to the interests of readers who are not scientists, and it is distinguished by first-rate photographs and original color drawings.