IUCN Red List

What the IUCN Red List means

The IUCN Red List of Threatened Species is a global inventory of how close species are to extinction. It's run by the International Union for Conservation of Nature (IUCN) and was established in 1964.

For each species it covers, the Red List gives a category (such as Vulnerable or Endangered) plus supporting information on range, population size, habitat, threats and conservation actions. Governments, scientists, zoos and conservation groups use it to decide where help is needed most.

As of 2026, IUCN reports that more than 175,900 species have been assessed, and more than 49,500 of them (about 28%) are threatened with extinction.

The Red List categories

Assessed species fall into one of these categories, from lowest to highest risk:

• Least Concern (LC): widespread and not close to qualifying as threatened.
• Near Threatened (NT): close to qualifying, or likely to soon.
• Vulnerable (VU): high risk of extinction in the wild.
• Endangered (EN): very high risk.
• Critically Endangered (CR): extremely high risk.
• Extinct in the Wild (EW): survives only in human care or outside its native range.
• Extinct (EX): no reasonable doubt that the last individual has died.

Two more labels sit outside the scale. Data Deficient (DD) means there isn't enough information to judge the risk. Not Evaluated (NE) means the species hasn't been assessed yet.

The three middle categories, Vulnerable, Endangered and Critically Endangered, are together called threatened.

How species are assessed

The Red List uses a fixed rulebook, the IUCN Red List Categories and Criteria (Version 3.1). Each species is checked against five criteria, labeled A to E:

• A: how fast the population is shrinking
• B: how small and fragmented its range is
• C: how small and declining the population is
• D: whether the population or range is very small
• E: what modeling says about the probability of extinction

A species only needs to meet one criterion to qualify for a category. Experts in specialist groups do the assessments, they are peer reviewed, and IUCN aims to reassess every species at least once every ten years.

The Red List vs. the Endangered Species Act

The Red List is global and scientific. The Endangered Species Act is a U.S. law with its own "endangered" and "threatened" listings, decided by federal agencies. The two lists are made separately and often disagree. On Feather & Fang, animal pages show each species' IUCN Red List category.

Why it matters at the zoo

Zoo signs often show a species' Red List status, and many accredited zoos focus their breeding work on threatened species through Species Survival Plans. You can browse animals by status on our animals pages, or read more about how zoos help conservation.