Under the Endangered Species Act of December 28, 1973, there are certain criteria that an animal species must meet for the U.S. Fish and Wildlife Service (FWS) to classify it as endangered. While the FWS regulates freshwater and land animals, the National Marine Fisheries Service has jurisdiction over marine species and those that live in both saltwater and fresh water. (Pictured below: Bengal Tiger)
For a species to wind up on the endangered list, it must be in grave danger of its extinction in a large part of its range and habitat. Private citizens or conservation groups petition for the animal's welfare and the agencies involved review the information and decide if the animal warrants listing as endangered.
Loss of habitat, overhunting or fishing, and the use of pesticides are among the causes for animals to make the endangered-species list. A threatened species is an animal that is on its way to inclusion on the endangered list.
When the habitat of an animal is in danger of destruction--in the present time or at some time in the future--the animal will be on the endangered species list.
Species that have fallen victim to disease or predation by another species can become endangered, as can those that are utilized too much for commercial, scientific and recreational goals.
Once a species is endangered the proper agency will take the necessary steps to protect it, such as curtailing hunting of the animal and stopping anyone from selling or buying the creature. The agency draws up a recovery plan for the species and puts it into effect.