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 span.
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 identified 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 very small ranges or highly specialized habitats. There are far fewer mammal species than plant species and a much higher proportion of them (more than 25 percent) are at risk, particularly many 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.
The main causes of species declines include habitat destruction, overexploitation, pollution, climate change and the spread of invasive species. Many critically endangered species simultaneously face several of these threats.
One of the best-known examples of a critically endangered animal is the Amur leopard, of which fewer than one 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, 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 appropriate areas (to reduce lead poisoning), protecting nesting sites, and 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 original 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 likewise extinct in the wild and only survives in collections.
The pygmy Rwandan waterlily, the smallest known waterlily, was once believed to be extinct in the wild but now survives thanks to the discovery of few small wild populations and conservation efforts. 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.