IUCN Red List

First recorded in 1960–65

The International Union for Conservation of Nature (IUCN) is recognized as the leading authority on the conservation status of plant and animal species throughout the world. Its Red List of Threatened Species (commonly called the IUCN Red List ) was created in 1964 and has become the most comprehensive global inventory of at-risk species.
The classifications and defining criteria for the IUCN Red List have changed over the years to accommodate the ever-advancing means by which a conservation status is determined. As the knowledge and observation of species have improved, so has the analysis of such crucial information as geographic distribution, population fragmentation, and of course rate of decline. As of 2018, the IUCN Red List classifies species into these categories:
• extinct (EX) = having no living member remaining, either in the wild or in captivity.
• extinct in the wild (EW) = having members living only in captivity or as a naturalized population.
• critically endangered (CR) = having the highest risk of extinction among threatened species.
• endangered (EN) = threatened with extinction.
• vulnerable (VU) = likely to be classified endangered in the near future unless circumstances that threaten reproduction and survival improve.
• near threatened (NT) = inclined to be threatened with extinction but not yet qualified as vulnerable.
• conservation dependent (CD) = dependent on conservation practices to prevent its becoming threatened with extinction.
• least concern (LC) = assessed to be thriving, with a distribution or population status that is neither threatened nor near threatened.
• data deficient (DD) = lacking a properly assessed conservation status due to insufficient information.
• not evaluated (NE) = not having been studied and assessed for conservation status by the IUCN.

It is sometimes assumed that “threatened” is one of the Red List categories, but the term threatened species is used by the IUCN to include all species that are classified under these three categories: vulnerable , endangered , and critically endangered .
Because extensive research and verification are required before a species is classified as either extinct or extinct in the wild , there may be any number of critically endangered species that are in fact extinct or extinct in the wild. The IUCN’s avian authority, BirdLife International , has therefore recommended—and the IUCN has adopted—two subcategories under the critically endangered category:
• possibly extinct (PE) = so critically endangered that evidence of existence is profoundly limited and extremely difficult to verify.
• possibly extinct in the wild (PEW) = so critically endangered that evidence of existence outside of captivity or a naturalized population is profoundly limited and extremely difficult to verify.