Endangered Animals: IUCN Categories Explained With Examples

What is the IUCN Red List?

The IUCN Red List of Threatened Species was set up in 1964 by the International Union for Conservation of Nature, a global network of governments and conservation groups. Experts assess each species against the same set of rules, so a beetle, a frog and a whale can be compared on one scale. Assessments are repeated every few years, and a species can move up or down as its situation changes.

The Red List covers animals, plants and fungi. Coverage is best for well-studied groups: according to the IUCN, about 41% of amphibians, 38% of sharks and rays, 26% of mammals, 21% of reptiles and 11% of birds are threatened, along with 44% of reef-building corals.

The IUCN categories explained

Vulnerable, Endangered and Critically Endangered together are called threatened. In everyday speech, “endangered” is often used for all three.

How does a species qualify as endangered?

The IUCN uses five criteria, labeled A to E. A species is placed in the highest category for which it meets any one of them:

For criterion A, the higher percentage applies when the causes of decline have stopped and are understood, the lower one when they have not. “Mature individuals” means adults able to breed, so a population of 1,000 animals may count as only a few hundred.

Endangered on the Red List vs endangered by law

The Red List is a scientific assessment of global risk and gives no legal protection. Laws use their own lists. The US Endangered Species Act, passed in 1973, classifies species as “endangered” or “threatened” within the United States, and the European Union protects species under its Habitats Directive. The lists do not always match: the brown bear is Least Concern worldwide, yet grizzly bears in the lower 48 states are protected as threatened under US law.

Why animals become endangered

A major global assessment by IPBES, the UN-backed science panel on biodiversity, ranked the drivers of loss in 2019. In order of overall impact:

• Habitat loss: forests, grasslands and wetlands turned into farms, plantations, mines and cities.
• Direct exploitation: overfishing, poaching and the wildlife trade.
• Climate change: shifting temperatures, melting sea ice and dying coral reefs.
• Pollution: pesticides, plastics, oil and lead.
• Invasive species: introduced rats, cats, snakes and predatory fish, especially on islands.

Disease is also important. The chytrid fungus, spread around the world partly through the animal trade, has contributed to declines in hundreds of amphibian species.

20 endangered animals around the world

A few numbers show how close some species are to the edge. The vaquita has probably dwindled to around 10 or fewer animals. About 380 North Atlantic right whales remain, according to recent estimates. The IUCN’s 2022 assessment put the wild tiger population at roughly 3,700–5,600. Only a few hundred kākāpō exist, and every bird is named and monitored. Read more in Why is the vaquita almost extinct? and How many right whales are left?

Many great apes are in trouble. All three orangutan species are Critically Endangered, mostly because of forest loss, as explained in Why are orangutans endangered? The mountain gorilla, a subspecies of the eastern gorilla, is a rare bright spot: careful protection lifted its numbers above 1,000, and in 2018 it moved from Critically Endangered to Endangered. See How many mountain gorillas are left?

Extinct in the Wild: the last step before extinction

Some animals now survive only in zoos and breeding centers. The Hawaiian crow, or ʻalalā, the Guam kingfisher and Spix’s macaw of Brazil are all listed as Extinct in the Wild. Each disappeared from nature because of a mix of habitat loss, introduced predators such as the brown tree snake on Guam, disease and trapping for the pet trade. Conservationists have begun releasing some of them back into the wild, but it takes many years before a released population can be called self-sustaining. For species already lost, see our list of recently extinct animals.

Success stories: animals that recovered

• Humpback whale: commercial hunting of humpbacks was banned in 1966. The species is now listed as Least Concern, with a global population estimated at about 135,000 whales in 2018, including about 84,000 mature adults.
• Arabian oryx: hunted out of the wild by 1972, it was bred in captivity and reintroduced from 1980. In 2011 it became the first animal to move from Extinct in the Wild to Vulnerable.
• Scimitar-horned oryx: declared Extinct in the Wild in 2000, it was reintroduced in Chad from 2016 and moved to Endangered in 2023.
• Iberian lynx: only 94 were left in 2002. After decades of habitat work, rabbit restoration and releases in Spain and Portugal, more than 2,000 lived in the wild by 2024, and the species moved from Endangered to Vulnerable.
• European bison: wiped out in the wild in the 1920s, it was rebuilt from zoo animals. Several thousand now live in free-ranging herds in Poland, Belarus and other parts of Europe, and in 2020 it moved from Vulnerable to Near Threatened.
• Giant panda: after decades of forest protection, a 2014 national survey counted 1,864 wild pandas, and in 2016 the species moved from Endangered to Vulnerable. Read more in Are giant pandas still endangered?

Not every recovery is complete. The California condor fell to just 27 birds in 1987, all taken into captivity. Thanks to breeding and releases, the world population had grown to 607 by late 2025, but lead poisoning from ammunition left in carcasses keeps it Critically Endangered.

What helps endangered animals?

The most successful efforts combine several measures: protecting and reconnecting habitat, enforcing laws against poaching and illegal trade, reducing bycatch in fisheries, removing invasive predators from islands and, for the rarest species, breeding in captivity and releasing animals back into the wild. International agreements such as CITES, which has regulated trade in endangered species since 1975, help control demand across borders. Regular Red List reassessments show where these efforts are working and where species are still slipping toward extinction.