What do the IUCN Red List categories mean?

The IUCN Red List of Threatened Species is the world's most widely used measure of how close a species is to extinction. Run by the International Union for Conservation of Nature since 1964, it has assessed more than 175,900 species, and more than 49,500 of them, 28%, are threatened with extinction, according to the IUCN Red List.

The nine categories

Experts place each species in one of nine categories, based on five criteria that look at the size and range of its population and how fast it is declining or recovering. From lowest to highest risk:

• Not Evaluated: not yet assessed. These species are not published on the list.
• Data Deficient: not enough information on numbers or distribution to judge the risk.
• Least Concern: assessed and not close to any threatened category.
• Near Threatened: close to qualifying for a threatened category, or likely to soon.
• Vulnerable: facing a high risk of extinction in the wild.
• Endangered: facing a very high risk of extinction in the wild.
• Critically Endangered: facing an extremely high risk of extinction in the wild.
• Extinct in the Wild: survives only in captivity, in cultivation or as a population well outside its past range.
• Extinct: no reasonable doubt that the last individual has died.

What “threatened” means

Vulnerable, Endangered and Critically Endangered together are called “threatened,” the Red List FAQ says. Critically Endangered species can also be flagged as Possibly Extinct or Possibly Extinct in the Wild when they have not been seen for a long time but extinction is not yet certain.

The share of threatened species varies a lot between groups. According to the Red List, 71% of cycads, 44% of reef-building corals, 41% of amphibians, 38% of sharks and rays, 26% of mammals and 11% of birds are threatened.

Why a species changes category

Species are meant to be reassessed every five to 10 years. A change of category can be “genuine,” because threats eased or grew, or “non-genuine,” because new data became available, the species was split or merged by taxonomists, or an earlier assessment contained an error, IUCN explains. Only genuine changes feed into the Red List Index, which tracks whether species are doing better or worse overall.

Genuine improvements often follow reintroductions, habitat protection or legal protection. IUCN also counts Extinct in the Wild species among threatened ones in its statistics, because a successful reintroduction can move them back into a threatened category.

Lost and found

Declaring a species extinct is difficult, because almost nobody sees the last individual die. Some species listed as extinct are later found alive, so-called Lazarus species, and IUCN warns that declaring a species extinct too early can make it disappear for real if protection is withdrawn. Species thought lost can turn up again: the Pacific pocket mouse, once thought extinct, was rediscovered in 1993 and has since been reintroduced to a third site in California.

What the list does not tell you

The Red List measures current risk; it does not predict when a species will go extinct. It also covers only a small part of life on Earth. Of more than 2 million described species, less than 10% have been assessed, and IUCN aims to reach 260,000 assessed species under its strategic plan for 2021 to 2030.

Many of our stories mention a species' Red List status. Recovery stories are collected under species recovery.