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Dam Animals



The dry spell we're experiencing this spring may have an upside: it will limit run-ins between man and beaver.

The spring rains that cause rising rivers usually signal the beginning of beaver-busting season. April and May are traditionally when towns and park districts along Illinois rivers rip out beaver dams built during the winter. If the beavers won't move, they'll be killed or forcibly relocated. But with rainfall as much as eight inches below normal and river levels low even with late snows, the critters' impact shouldn't be as noticeable.

Beavers made Chicago. Beaver skins were the reason Chicago became a trading center. Until the 1970s, when antifur consciousness soared and area trapping stopped, beaver dams were just a rural problem. Since then, the populations have grown and moved down the I & I Canal, the Chicago River, and the Des Plaines River. They've been spotted downtown on the north branch of the Chicago River near Wolf Point, farther north near the Green Dolphin Street nightclub at Ashland and Webster, and near Ping Tom Park in Chinatown.

What's the problem? Beavers eat bark, and prefer some tree species over others, including those $400 aspens suburbanites like to plant. Their dams plug up culverts and cause floods. And they're often blamed for the dispersal of the intestinal parasite Giardia lamblia, which causes nausea and diarrhea in humans. Some call it beaver fever, but deer, muskrats, dogs and cats, and even humans can carry the parasite.

The most notorious city beavers in recent history lived in Jackson Park, where three years ago they gnawed up about 75 trees on Wooded Island, a bird-watching hot spot in the park's lagoon. Birders raised a ruckus, and in an agreement with the Chicago Park District, a DeKalb wildlife control specialist named Rob Erickson trapped the 13 animals responsible and moved them to an undisclosed location in northern Cook County. "Our policy is to remove them in a humane fashion and then relocate them in a place that can accommodate their eating and damming needs," Park District spokeswoman Angie Amores explains.

In the suburbs, the problem's more widespread and the solutions more varied. In Lake County, most of the beavers live along the creeks feeding the Des Plaines River. It's up to Jim Anderson, natural resource manager for the Lake County Forest Preserve, to solve beaver problems on the county's 24,000 forest preserve acres. Anderson says they tend to leave the animals in place unless the dams cause flooding on adjacent roads or private property--for instance, at the Wadsworth Savanna site this past week, a beaver that's been clogging culverts for two years elicited a complaint from a neighbor whose backyard was flooding. "We'll have to go out and take a look at it," Anderson says.

To alleviate flooding, Anderson and his crew often run pipes through the dams to try to lower the upstream water levels. Or they tear out the dam altogether and see if the beavers relocate on their own. A couple times in the last two years Anderson has tried hiring licensed private trappers to move beavers to other areas in Lake County, but one of the beavers died. Anderson says the transfer stresses the animals out, and besides, there aren't many places to take them where they don't just cause problems for someone else.

Erickson says he's never had a beaver die in 30 years of planned live trapping. "They're very hardy animals," he says. "That trapper just doesn't know what he's doing." Erickson's preferred no-kill method is a galvanized-cable snare that catches the beaver behind its front legs. Once caught, the beavers can surface safely and leave or enter the water as needed, and Erickson says they're in fair shape when he returns to remove them, which can be up to 12 hours later.

Anderson says killing beavers, or "removing them from the natural world," as he puts it, is a last resort in Lake County; when it comes to that, again, a licensed trapper is called in. Anderson says he believes the captured animals are shot in the head with a .22, but he doesn't know for sure. Another method involves trapping them underwater, where they die of carbon dioxide narcosis. (Beavers have valves in their noses that keep water out and prevent them from simply drowning.)

Some of this may help explain why you're not likely to see beavers during the day. It's believed they used to be diurnal but have been forced over the centuries to become nocturnal, according to Peter Busher, an expert at Boston University. "Think about it," he writes in an E-mail. "Humans have been hunting beavers (to extinction in some cases) in Europe for thousands of years. [They've] been hunting and using beavers in North America since they arrived 10,000-20,000 years ago. In many places beavers are not under hunting pressure, yet they maintain the mostly nocturnal way of life. It may be that being nocturnal gives beavers more of an advantage against predation and does not negatively influence their ability to procure food."

The best place in the area to see beavers' handiwork, though, is off Highway 41 near the Wisconsin border at the Des Plaines River Wetlands Demonstration Project in Wadsworth.

Donald Hey, one of the project's heads, is a great admirer of the beaver--he credits it, in no modest terms, for the entire North American drainage system. Glaciers carved deep cuts in the earth, he explains; then prehistoric beavers slowed the raging rivers with dams. The rivers widened, occasionally flooding and moving silt and effluvia over the banks to make rich meadowlands.

In 1985, with support from environmental groups, Chicago corporations, and the state and federal governments, Hey and others acquired 550 acres from the Lake County Forest Preserve and turned a series of gravel pits off Highway 41 into a patchwork of ponds, marshes and wetlands. The beavers came, of their own accord, from the Des Plaines River. In 1992, Hey helped start the not-for-profit Wetlands Initiative, which now administers 17 other restoration sites in the Illinois River watershed as well.

Hey, an affable 63-year-old Missouri native who got his doctorate in hydrology from Northwestern, says giant Pleistocene-epoch beavers (Castoroides ohioensis) as big as black bears roamed the Great Lakes about 10,000 years ago. By the time of Columbus, according to paleontological and archaeological estimates, there were more than 400 million modern beavers (Castor canadensis) on the North American landscape. Hey walks me past a site at the Wadsworth project where in the mid-90s remains of 8,500-year-old trees with gnaw marks were found by University of Illinois and Illinois State Museum archaeologists.

"Well look at that," says Hey, slipping down a small embankment to find a small uncharted beaver dam on a small creek. The two-foot dam allows a trickle of water to fall two feet. The water behind the dam is pooling into a pond no bigger than a beach ball.

We walk by several more ponds--there are four or five independent beaver colonies at Wadsworth, each made up of a monogamously mated pair, two or three kits (which are born in the spring), and one or two yearlings. A beaver compound is a remarkable engineering feat, with a curved dam, dens built into the river bank, protected food caches, and an extensive network of trails both above and below the surface of the water.

Beavers dam rivers not to altruistically reshape the world, of course, but rather to defend themselves. Central to the den's interior is a food platform where all manner of interior chambers intersect. The platform needs to be slightly higher than the water level. But the water level inside the den must also be high enough to keep out marauding otters and minks. Hey says when a biological diversity study of the area was first undertaken 20 years ago, researchers reported quite a large population of minks, a species thought to be long gone. They turned out to be the descendants of escapees from a shuttered mink farm a few miles away.

So, to summarize: Beavers shaped the land we live on. We hunted them to near extinction for commerce. Then we protected their fur and allowed the populations to grow. Now we're moving them or killing them because they're encroaching on our habitat, which used to be theirs.

"I think all the bird watchers should be put in a cage, not the beavers," says Erickson. "What have the birds done for us?"

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