Bears escape holding area at Milwaukee Zoo

<p>SAN FRANCISCO - MAY 18: A grizzly bear, an endangered animal species, sits in an exhibit at the San Francisco Zoo May 18, 2007 in San Francisco, California. The U.S. celebrates the second annual Endangered Species Day with zoos, aquariums, parks and a host of educational institutions educating the public on how important it is to protect wildlife and the growing number of endangered species, both animals and plant life. (Photo by Justin Sullivan/Getty Images)</p>