The beaver is a primarily nocturnal semi-aquatic rodent. Genus Castor includes two species, North American Beaver (Castor canadensis) and European Beaver (Castor fiber), native to Eurasia. Beavers are known for their extensive building projects consisting of dams, canals, and lodges. They are the second-largest rodent in the world, after the capybara.
Their colonies create one or more dams to provide still, deep water to protect against predators, and to float food and building material. The North American beaver population was once more than 60 million, but as of 1988 was ~12 million. This population decline is due to extensive hunting for fur, for glands used as medicine and perfume, and because their harvesting of trees and flooding of waterways may interfere with other land uses. In other words, man has usurped most of this creature's habitat and we don't like flooding.
I might add, McKee marsh is home to a once-healthy population of coyotes. Many's the time I've suddenly walked up on one only to have them slink away into the trees or burst into full flight; their howls in a twilit winter woods makes the hair on the back of my neck stand up. The coyotes here are part of a much larger clan that lives on the grounds of Fermilab, scarcely 2 miles to the west. In 2010, the unfortunate creatures began hunting in the suburban backyards of Wheaton and Warrenville – and animal control immediately started shooting and trapping them into submission. After all, we can't have the wild animals lunching on some poor slob's shih-tzu, can we?
This new activity (I've not seen beaver activity in DuPage County since 2002, alongside the West branch of the DuPage River in Winfield Illinois. That individual cut down a half-dozen trees, left and never returned (as of 2010). That beaver or beavers (or, at least, their descendants) may be responsible for this cutting as well – the small creek that drains this marsh runs into the same river, about 1/4 mile to the west. This is about 6 miles downstream from Winfield.
I believe these are transient populations, as the marsh this summer dwindled in fall to barely 3-4 feet of water in a very limited area. I have never seen any damming nor lodge building – just these trees cut down – and left lying in place (below).
Same island, Christmas Eve, 2010. Almost all the willows are cut down. Note – the beavers won't touch the invasive buckthorn also growing there.
In Chicago, several beavers have returned and made a home near the Lincoln Park's North Pond. The "Lincoln Park Beaver" has not been as well received by the Chicago Park District and the Lincoln Park Conservancy, which was concerned over damage to trees in the area. In March 2009, they hired an exterminator to remove a beaver family using live traps, and accidentally killed the mother when she got caught in a snare and drowned. Relocation costs $4,000-$4,500 per animal. Scott Garrow, District Wildlife Biologist with the Illinois Department of Natural Resources, opined that relocating the beavers may be "a waste of time", as there are records of beaver recolonizing North Pond in Lincoln Park in 1994, 2003, 2004, 2008 and 2009.
There's a reason for the phrase "Busy as a beaver."
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