The survival of wildlife is jeopardized by the loss of habitat, over-hunting or over-fishing, the introduction of diseases or parasites, attempts to eradicate "pest" species, and the capture of wild animals and fish for the pet trade, research, entertainment, or other industries. Once a population of animals is reduced by one or more of these human activities, it may be unable to withstand natural limiting factors in the wild—such as predation, limited food supply, or disease—that it might otherwise have survived.

The Endangered Species Act

The Endangered Species Act (ESA) was enacted to preserve endangered and threatened species and the habitats on which they depend for survival. An "endangered" species is one that is in danger of extinction throughout all or a significant portion of its range. A "threatened" species is one that is likely to become endangered in the foreseeable future.

The ESA works in two stages: First, the government protects a species from possible extinction, and then it takes steps to restore the species' numbers to the point where it is no longer threatened.

The U.S. Fish and Wildlife Service (USFWS) (and for some species, the National Marine Fisheries Service) is required to list a species as threatened or endangered if its existence is threatened by one or more of the following factors: (1) the present or threatened destruction, modification, or curtailment of its habitat or range; (2) overutilization for commercial, recreational, scientific, or educational purposes; (3) disease or predation; (4) the inadequacy of existing regulatory mechanisms; or (5) other natural or manmade factors affecting its continued existence.

A species may also be categorized as a "candidate" for protection if the USFWS finds that an ESA listing is "warranted" but "precluded" by other priorities. What this means in practice is that the USFWS may determine that a species meets the criteria for inclusion on either list, but that the agency has other, higher priority candidates that need more immediate attention.

The Role of States in Protecting Species

Wildlife species are often categorized by the states in which they occur, according to the extent to which they require protection. But the labels given to these categories vary by state. For example, species considered to require some level of protection are sometimes designated as "state endangered or threatened," "sensitive species," "species of management concern," "protected species," or "game species" (for which any hunting or other "take" is regulated).

Those species that a state considers not to require protection or regulation may be referred to as "unprotected species," or "pest species." These designations influence how the species are managed by state wildlife agencies. However, if a particular species is federally listed as threatened or endangered (or otherwise protected at the federal level), any protections provided by the state must be at least as restrictive as those provided at the federal level.

Other U.S. Laws

Besides the ESA, there are several other federal laws that protect endangered and threatened species, such as the Marine Mammal Protection Act (MMPA), the Migratory Bird Treaty Act (MBTA), The Bald and Golden Eagle Protection Act, the Wild Bird Conservation Act, and the African Elephant Conservation Act.

International Laws

Among the international treaties to protect endangered species are the Convention on Trade in Endangered Species of Fauna and Flora, the International Convention on the Regulation of Whales, and the Convention for the Protection and Development of the Marine Environment of the Wider Caribbean Region. The international treaties are implemented into and made a part of U.S. law through the enactment of various federal laws, such as the MBTA, the MMPA, and the ESA.