In 1988 a survey revealed that over 120 endangered or threatened species were known or suspected to occur in more than 140 units of the National Park System. Some species are found in many parks. The bald eagle nests, migrates, or winters in 71 parks, the peregrine falcon in 59. But most of the species are very restricted. Seventy-four are found in only one or two parks.
Many parks contain critical habitat.
Critical habitat, under the Endangered Species Act, is an area that has been designated by the Fish and Wildlife Service as essential to the conservation of an endangered species. Critical habitat has been designated in one or more parks for each of some two dozen endangered or threatened species. When a park has an endangered species, the staff tries to learn how many individuals there are, what areas they inhabit, and whether special management is required to maintain or increase the population. Park managers also consider the species that formerly occurred in the park and whether they can be reestablished. In some cases, management consists largely of recording the locations of endangered species, monitoring their well-being, and protecting their habitat.