An endangered species is a species having a very high risk of extinction in the near future, either worldwide or in a particular region. Species become endangered due mainly to habitat depletion and loss of genetic variation.
The International Union for Conservation of Nature (IUCN) Red List classifies the global conservation status of many species, and various other agencies assess the status of species within particular areas. The IUCN considers a species as endangered when it meets one or more criteria for a declining population and diminished geographic distribution; for example, when a species population is reduced by 20% within five years and has fewer than 2,500 mature individuals remaining, the species is considered endangered. In 2026, the IUCN Red List named 49,500 species worldwide as threatened for extinction.
Many nations have laws that protect conservation-reliant species which, for example, forbid hunting or harvesting, restrict land development, or create protected areas. Some endangered species are under protection by extensive conservation efforts, such as captive breeding and habitat restoration. Human activity is a significant factor causing species to become endangered.
Threat factors A species becomes endangered mainly because of habitat loss and diminished genetic variation.
Loss of habitat Habitat loss can occur naturally or as the result of human activity, such as by development of agriculture, food requirements, housing, or industry, and their collective impacts on the environment.
Climate change refers to long-term changes in weather patterns causing shifts in surface temperature and rainfall. Climate change endangers species because it disturbs their native ecosystems. Efforts to understand and mitigate the impact of climate change on species through scientific research, modelling, and conservation evaluate the current condition of species, their genetic variation, and how changes in their environment may affect their survival.
Habitat loss can also occur by introduction of an invasive species.
Loss of genetic variation A diversity of traits within a species is its genetic variation, enabling a species to make durable adaptations to habitat changes; typically, genetic variation is highest in species with a large population. Genetic variation is diminished in endangered species with reduced populations by inbreeding, disease, human activity, monoculture, and climate change.
Criteria for endangered species According to the IUCN Red List, a species may become endangered when it meets one or more of several criteria: Population decline. A species is endangered when its population diminishes by 50% to 70%, an assessment made over 10 years or three generations, whichever is longer. Geographic range. The extent of occurrence of an endangered species is less than 5,000 square kilometres (1,930 square miles), and it occupies an area less than 500 square kilometres (193 square miles). Population size. A species is endangered when its population declines by 20% within five years and there are fewer than 2,500 mature individuals remaining. Population restrictions. When a species population is reduced to 250 mature individuals, it is classified as endangered. Probability of extinction. In the wild, a species has a probability of extinction when its population is reduced to at least 20% within 20 years or five generations.
Conservation status
The conservation status of a species indicates the likelihood that it will become extinct. Multiple factors are considered when assessing the status of a species, such as the number remaining, the overall increase or decrease in the population over time, breeding success rates, or known threats. The IUCN Red List of Threatened Species is the best-known worldwide conservation status listing and ranking system. Species are classified by the IUCN Red List into nine groups set through criteria such as rate of decline, population size, area of geographic distribution, and degree of population and distribution fragmentation.
Also included are species that have gone extinct since 1500 CE. When discussing the IUCN Red List, the official term "threatened" is a grouping of three categories: critically endangered, endangered, and vulnerable.
Extinct (EX) – There are no known living individuals Extinct in the wild (EW) – Known only to survive in captivity, or as a naturalized population outside its historic range Critically Endangered (CR) – Highest risk of extinction in the wild Endangered (EN) – Higher risk of extinction in the wild Vulnerable (VU) – High risk of extinction in the wild Near Threatened (NT) – Likely to become endangered in the near future Conservation Dependent (CD) – Low risk; is conserved to prevent being near threatened, certain events may lead it to being a higher risk level Least concern (LC) – Very low risk; does not qualify for a higher risk category and not likely to be threatened in the near future. Widespread and abundant taxa are included in this category. Data deficient (DD) – Not enough data to make an assessment of its risk of extinction Not evaluated (NE) – Has not yet been evaluated against the criteria.
Over 50% of the world's species are estimated to be at risk of extinction, but the frontiers between categories such as "endangered", "rare", or "locally extinct" species are often difficult to draw given the general paucity of data on most of these species. This is notably the case in the world's oceans, where distances are vast and endangered species not seen for decades may go extinct unnoticed.
Internationally, 195 countries have signed an accord to create Biodiversity Action Plans that will protect endangered and other threatened species. In the United States, such plans are usually called Species Recovery Plans.
IUCN Red List
Though labelled a list, the IUCN Red List is a system of assessing the global conservation status of species that includes "Data Deficient" (DD) species – species for which more data and assessment is required before their situation may be determined – as well species comprehensively assessed by the IUCN's species assessment process. The species under the index include: mammals, birds, amphibians, cycads, and corals. Those species of "Near Threatened" (NT) and "Least Concern" (LC) status have been assessed and found to have relatively robust and healthy populations, though these may be in decline. Unlike their more general use elsewhere, the List uses the terms "endangered species" and "threatened species" with particular meanings: "Endangered" (EN) species lie between "Vulnerable" (VU) and "Critically Endangered" (CR) species. In 2026, the IUCN Red List identified 49,500 species worldwide as threatened to become extinct. The threatened list includes 71% of cycad plants, 44% of reef corals, 41% of amphibians, and 38% of sharks and rays, among others.
In Brazil
Brazil is one of the most biodiverse countries in the world, if not the most. It houses not only the Amazon forest but the Atlantic forest, the savanna-like Cerrado among other biomes. Due to the high density of some of its well-preserved rainforests, wildlife trafficking, which along with deforestation is one of the biggest endangerment drivers in Brazil, has become a challenge. Brazil has a broad legal system meant to protect the environment, including its Constitution, as well as several federal, state and local government agencies tasked with protecting the fauna and flora, fining individuals or companies linked to environmental crimes and confiscating illegally taken wildlife. Though such agencies can collect their data, each system operates relatively on its own when it comes to wildlife trafficking. However, both the agencies and the NGO's working in Brazil agree that the birds account for about 80% of trafficked species in the country.
The relation between wildlife smuggling, other environment crimes under the Brazilian law such as deforestation, and endangered species is particularly intricate and troubling since the rarer the animal or plant gets the most targeted and valuable they become in the black market, which leads to more endangered species in its turn.
Additionally, some environment experts and scientists point to the disbanding of environment agencies and the repeal of laws in Brazil under the presidency of Jair Bolsonaro as one of the reasons behind a surge in the number of endangered species. In one occasion during his presidency some fines totalling US$6.7 billion on environment criminals were revoked and at least one fine (related to illegal fishing) imposed on Bolsonaro himself was cancelled and the agent who fined him was demoted.
In the past, Brazil has successfully saved the endemic golden lion tamarin from extinction. Massive campaigns to raise awareness among people by NGO's and governments, which included printing depictions of the golden lion tamarin in the 20 reais Brazilian banknotes (still in circulation), are credited with getting the species out of the critically endangered animals list.
In the United States
There is data from the United States that shows a correlation between human populations and threatened and endangered species. Using species data from the Database on the Economics and Management of Endangered Species database and the period that the Endangered Species Act (ESA) has been in existence, 1970 to 1997, a table was created that suggests a positive relationship between human activity and species endangerment.
Endangered Species Act Under the Endangered Species Act of 1973 in the United States, species may be listed as "endangered" or "threatened". The Salt Creek tiger beetle is an example of an endangered subspecies protected under the ESA. The US Fish and Wildlife Service, as well as the National Marine Fisheries Service are held responsible for classifying and protecting endangered species. They are also responsible for adding a particular species to the list, which can be a long, controversial process. The act adds numerous other provisions as well, including the designation of endangered species' critical habitats and a requirement to develop a recovery plan for the species. On top of this, the ESA protects endangered species from government policies; for instance, federal agencies must consult the Fish and Wildlife Service or the National Marine Fisheries Service before executing any action that may jeopardize threatened species or their habitats.
Some endangered species laws are controversial. Typical areas of controversy include criteria for placing a species on the endangered species list and rules for removing a species from the list once its population has recovered. Whether restrictions on land development constitute a "taking" of land by the government; the related question of whether private landowners should be compensated for the loss of uses of their areas; and obtaining reasonable exceptions to protection laws. Also lobbying from hunters and various industries like the petroleum industry, construction industry, and logging, has been an obstacle in establishing endangered species laws.
The Bush administration lifted a policy that required federal officials to consult a wildlife expert before taking actions that could damage endangered species. Under the Obama administration, this policy was reinstated.
Being listed as an endangered species can have an indirect negative effect since the perceived increase in rarity could make a species more desirable for collectors and poachers. This effect is potentially reducible, such as in China where commercially farmed turtles may be reducing some of the pressure to poach endangered species.