A critically endangered species is defined by the International Union for Conservation of Nature (IUCN) as a species that faces an extremely high risk of extinction in the wild. This is the highest threat level for species that still exist in nature, just one step below extinct in the wild. A species can be listed as critically endangered if, for example, its population has dropped by about 80 to 90 percent over ten years or three generations, or if there are very few mature individuals left (often fewer than about 250), or if scientific analysis shows at least a 50 percent chance that it will go extinct in the wild within that same time frame.
This compares with an endangered species, which is defined by the IUCN as facing a very high risk of extinction in the wild, with fewer than about 250 to 2,500 individuals and a greater than 20 percent probability of extinction within about 20 years or five generations. A vulnerable species is defined as facing a high risk of extinction in the wild with fewer than about 1,000 to 10,000 individuals and a greater than ten percent chance of extinction within about 100 years. These categories are used globally to prioritize conservation actions, allocate funding, and influence laws and policies that protect species and their habitats.
As of 2023, about 9,760 of the roughly 157,000 species assessed by the IUCN were classified as critically endangered, some of which were flagged as possibly extinct or possibly extinct in the wild. A more recent survey reports that at least 10,443 animal, plant and fungal species are considered critically endangered. What is missing from this data is the fact that there is a vast number of species that are still unknown to science and that many of them are also endangered.
On the IUCN Red List, vascular plants (including groups such as conifers and cycads) constitute a very large share of all species assessed as threatened or critically endangered, reflecting, among other factors, the enormous diversity of plants and the fact that many have tiny ranges or highly specialized habitats. Mammals have a far smaller number of species than plants but a relatively high proportion at risk, so they include many critically endangered species such as some primates, large herbivores, and marine mammals. Birds, in contrast, tend to have fewer critically endangered species than plants or mammals, both in absolute numbers and as a percentage of all bird species, although some groups (e.g., ground-nesting seabirds and island parrots) are severely threatened.
Overall, the main causes of species declines include habitat destruction, overexploitation, pollution, climate change and the spread of invasive species. Many critically endangered species face several of these threats at once.
One of the best-known examples of a critically endangered animal is the Amur leopard, of which fewer than a hundred remain in the wild. The main threats have been habitat loss and poaching. Protection is focused on anti-poaching patrols, protected reserves, and strict trade bans on their fur.
The population of the Sumatran orangutan in Indonesia has dropped to only a small fraction of its original level as a result of forest destruction for palm oil plantations and logging. Conservation measures include protecting and restoring the remaining forests, strengthening standards for how palm oil is grown and traded so that it no longer drives deforestation, and rescuing and rehabilitating orangutans that have been captured or displaced.
The California condor, once extinct in the wild, is now slowly recovering through captive breeding and reintroduction, but is still critically endangered. Major actions include banning lead ammunition in key areas (to reduce lead poisoning), protecting nesting sites, and ongoing release and monitoring programs.
Among the thousands of critically endangered plants listed in the IUCN Red List is the golden fuchsia, a shrub that disappeared from its forest location in Mexico but survives in cultivated collections. The franklin tree, once native to the Altamaha River area in the U.S. state of Georgia, is also extinct in the wild and now only survives in cultivated collections. The pygmy Rwandan waterlily, the smallest known waterlily, was once thought to be extinct in the wild but now survives due to conservation efforts and a few rediscovered wild populations in Rwanda. The blue amaryllis, native to the rocky, high-altitude mountains of Brazil, is threatened by habitat destruction, wild collecting, and frequent fires. It is now maintained through cultivation and seed banks.