WASHINGTON – AUGUST 29: Two North American beavers check out a man-made beaver dam in the new beaver enclosure during a sneak peak of the new American Trail at the Smithsonian National Zoo August 29, 2012 in Washington, D.C. There are three beavers in the enclosure, Chipper, Buzz and Willow, all born in June of 2000. The trail, featuring animals and horticulture native to the Americas, opens to the public on September 1. (Photo by Allison Shelley/Getty Images)