The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also called the IUCN Red List or Red Data Book, was created in 1964. It is a list that shows the global conservation status and risk of extinction for different species. Some countries and groups also make Regional Red Lists, which look at the risk of extinction for species in specific areas managed by governments or organizations.

The main goals of the Red List are to share scientific information about the status of species worldwide, to highlight how serious the loss of biodiversity is, to help shape national and international decisions, and to provide guidance for protecting species and their habitats.

Important groups that assess species include BirdLife International, the Institute of Zoology (a research group part of the Zoological Society of London), the World Conservation Monitoring Centre, and many Specialist Groups within the IUCN Species Survival Commission (SSC). These groups and organizations are responsible for evaluating the status of nearly half of all species on the Red List.

The IUCN plans to reassess the category of every species at least once every ten years, and more often if possible. These reassessments are done by expert groups called Red List Authorities (RLA), which are part of the IUCN Species Survival Commission. These groups evaluate species, groups of species, or areas. For example, BirdLife International is responsible for all bird species. The Red List unit works with staff from the IUCN Global Species Programme and its partners to find new groups to join as Red List Authorities.

The number of species assessed for the Red List has grown over time. As of 2023, 150,388 species have been studied. Of these, 42,108 are at risk of extinction due to human activities, such as overfishing, hunting, and land development.

History

Initially, the Red Data Lists were created for experts and were made in a format with pages that could be added or removed easily.

The first two books in the Red List series were published in 1966 by conservationist Noel Simon. One book focused on mammals, and the other on birds.

The third book, published in 1968, covered reptiles and amphibians. It was created by René E. Honegger.

In 1970, the IUCN released the fifth volume in the series. This was the first Red Data List focused on plants (flowering plants only), compiled by Ronald Melville.

The last book made in the loose-leaf format was the fourth volume, which covered freshwater fishes. It was published in 1979 by Robert Rush Miller.

The first attempt to create a Red Data Book for the general public happened in 1969 with The Red Book: Wildlife in Danger. This book included many groups but mainly focused on mammals and birds, with smaller sections on reptiles, amphibians, fish, and plants.

The 2006 Red List, released on May 4, 2006, evaluated 40,168 species in total, plus an additional 2,160 subspecies, varieties, aquatic stocks, and subpopulations.

On September 12, 2007, the World Conservation Union (IUCN) released the 2007 IUCN Red List of Threatened Species. In this update, the classification of the western lowland gorilla (Gorilla gorilla gorilla) and the Cross River gorilla (Gorilla gorilla diehli) was raised from endangered to critically endangered. This change was due to threats such as the Ebola virus, poaching, and other factors. Russ Mittermeier, head of the IUCN's Primate Specialist Group, stated that 16,306 species are endangered with extinction, an increase of 188 from 2006 (total of 41,415 species on the Red List). The Red List includes the Sumatran orangutan (Pongo abelii) in the critically endangered category and the Bornean orangutan (Pongo pygmaeus) in the endangered category.

The 2008 Blue List was released on October 6, 2008, during the IUCN World Conservation Congress in Barcelona. It confirmed an extinction crisis, with nearly one out of every four mammals at risk of disappearing forever. The study showed that at least 1,141 of the 5,487 mammals on Earth are known to be threatened with extinction, and 836 are listed as data deficient.

The 2012 Red List was released on July 19, 2012, during the Rio+20 Earth Summit. Nearly 2,000 species were added, with 4 species added to the extinct list and 2 species added to the rediscovered list. The IUCN assessed a total of 63,837 species, revealing that 19,817 are threatened with extinction. Of these, 3,947 were described as "critically endangered," 5,766 as "endangered," and more than 10,000 as "vulnerable." At risk are 41% of amphibian species, 33% of reef-building corals, 30% of conifers, 25% of mammals, and 13% of birds. The IUCN Red List has listed 132 species of plants and animals from India as "critically endangered."

Categories

Species are grouped into nine categories by the IUCN Red List. These groups are determined using standards like how quickly a species is declining, the size of its population, how much area it lives in, and how broken up its habitat is. When high-quality data is not available, criteria are still used if possible threats or suspicions can be reasonably supported.

• Extinct (EX) – There is strong evidence that the species no longer exists.
• Extinct in the wild (EW) – The species survives only in captivity, in human care, or outside its natural habitat, as found after thorough searches.
• Critically endangered (CR) – The species is in a very serious and urgent situation.
• Endangered (EN) – The species faces a very high risk of disappearing from the wild and meets any of the criteria for Endangered.
• Vulnerable (VU) – The species meets one of the five Red List criteria and is at a high risk of dying out due to human actions unless humans take action.
• Near Threatened (NT) – The species is close to becoming endangered in the near future.
• Least Concern (LC) – The species is common and found in many areas.
• Data Deficient (DD) – There is not enough information to determine the risk of extinction.
• Not Evaluated (NE) – The species has not yet been assessed.

In the IUCN Red List, the term "threatened" includes the categories of Critically Endangered, Endangered, and Vulnerable.

The older 1994 list had one category called "Lower Risk," which included three subcategories:

• Conservation Dependent (LR/cd)
• Near Threatened (LR/nt)
• Least Concern (LR/lc)

In the 2001 system, Near Threatened and Least Concern became separate categories. Conservation Dependent was removed, and its species were added to the Near Threatened category.

The label "possibly extinct" (PE) is used by BirdLife International, the group responsible for bird assessments on the IUCN Red List. BirdLife International suggested making PE an official tag for Critically Endangered species. This has been accepted, along with a "Possibly Extinct in the Wild" tag for species that may be extinct in the wild but survive in captivity.

Versions

There have been several versions of the categories and criteria, starting in 1991. These versions include:

• Version 1.0 (1991)
• Version 2.0 (1992)
• Version 2.1 (1993)
• Version 2.2 (1994)
• Version 2.3 (1994)
• Version 3.0 (1999)
• Version 3.1 (2001)

Since 2001, all new IUCN assessments have used version 3.1 of the categories and criteria.

Criticism

In 1997, the IUCN Red List faced criticism because people questioned how well its data sources were explained. These concerns led the IUCN to work on improving how it records and shares information, and to include reviews by other experts to check the classifications of species on the list. The list also allows people to challenge its classifications if they believe the information or rules used are incorrect.

In the November 2002 issue of Trends in Ecology & Evolution, an article stated that the IUCN Red List and similar projects might be used in ways that lead to incorrect conclusions about the environment or influence how natural resources are used.

In the November 2016 issue of Science Advances, a research article reported serious problems with how the IUCN classifies species. The researchers said the IUCN’s method of categorization is outdated and needs improvement. They also stressed the importance of using geospatial data, such as satellite and aerial images, which are easier to access and include. The study questioned the accuracy of the IUCN’s classification methods and the correct placement of some species on the list. The researchers suggested that combining geographical data could help identify more species that may need to be moved to a higher risk category.