Annotated link http://www.diigo.com/bookmark/http%3A%2F%2Fwww.nps.gov%2Fgettinginvolved%2Findex.htm
Threatened: any species (other than a pest species) which is likely to become an endangered species within the foreseeable future.
Endangered: any species which is in danger of extinction throughout all, or a significant portion, of its range.
Sensitive: species that are not threatened or endangered, but may be at risk of becoming so