National wildlife refuges make up some of the habitat these animals need.

It has been 150 years since the federal government first set aside national public land expressly for the protection of wildlife—northern fur seals on Alaska's Pribilof Islands, which were then in danger of being wiped out due to the booming fur trade. Today, the units of public land most closely associated with preserving healthy animal populations are national wildlife refuges, and the U.S. has more than 560 of them, covering about 150 million acres and protecting hundreds of threatened or endangered species.

When an animal is listed under the Endangered Species Act, scientists at the Fish and Wildlife Service designate some stretches of land as "critical habitat," meaning they can provide all shelter, food and other essentials the species needs. These areas may be huge (more than 9 million acres in the case of the endangered Indiana bat) or very small (a few community parks in an affluent Southern California suburb, for the Palos Verdes blue butterfly). And in many cases, they are found within national wildlife refuges, underscoring the great value of our public lands as an ark safeguarding the nation's biodiversity.