The U.S. government recently proposed listing polar bears as threatened with extinction under the Endangered Species Act because the animals' sea ice habitat is melting. "Polar bears are one of nature's ultimate survivors," the Department of the Interior Secretary Dirk Kempthorne told reporters at a press conference. "They are able to live and thrive in one of the world's harshest environments. But there's concern that their habitat may literally be melting." Environmental groups quickly connected the announcement with scientific evidence that climate change is melting the iconic bear's Arctic habitat, causing the animals to go hungry and give birth less often. Polar bears live only in the Arctic, the northernmost region of Earth. The bears swim between ice floes to hunt their primary prey, the ringed seal.