The five IUCN criteria for extinction risk
The IUCN Red List assigns a threat category by applying five criteria, labelled A to E. A species is placed in the highest category for which it meets any one criterion. Critically Endangered is the most severe threatened category short of extinction. The thresholds below are the Critically Endangered cut-offs in the IUCN Categories and Criteria; Endangered and Vulnerable use the same five tests at less severe levels.
- Criterion A — population reduction. A decline of at least 90% where the causes are understood, reversible and have ceased, or at least 80% where they have not.
- Criterion B — geographic range. An extremely small extent of occurrence or area of occupancy, together with severe fragmentation or few locations, plus continuing decline or extreme fluctuation.
- Criterion C — small population and decline. Fewer than 250 mature individuals and a continuing decline.
- Criterion D — very small or restricted population. Fewer than 50 mature individuals, or a very restricted area of occupancy.
- Criterion E — quantitative analysis. At least a 50% probability of extinction in the wild within 10 years or three generations, whichever is longer, up to 100 years.
Meeting one criterion is enough. A species can be Critically Endangered because it is declining very fast even while thousands of individuals remain, or because only a few dozen mature individuals are left. The category is the result of the test, not a judgement about how alarming the animal looks.
The Red List is often described as a list of endangered species, which understates it. It is a standardised risk assessment framework applied to a growing subset of described species, with published criteria that allow two independent assessors to reach the same conclusion from the same data. That reproducibility is the point, and it is what distinguishes the categories from adjectives.
The categories, and what separates them
| Category | Meaning | What donors should note |
|---|---|---|
| Extinct | No reasonable doubt the last individual has died | Assigned conservatively; a species may be functionally gone long before it is listed |
| Extinct in the Wild | Survives only in captivity or outside its natural range | Recovery depends entirely on reintroduction programmes and suitable habitat existing |
| Critically Endangered | Meets the most severe thresholds for decline, tiny population or minute range | The category most used in fundraising, and the one where a single event can be decisive |
| Endangered | Meets severe but less extreme thresholds | Often the point at which intervention is still comparatively affordable |
| Vulnerable | Meets threatened thresholds at the lowest tier | Frequently ignored in appeals, and where prevention is cheapest |
| Near Threatened | Close to qualifying, or likely to qualify soon | An early-warning category, rarely funded |
| Least Concern | Does not currently qualify | Does not mean abundant everywhere; local extinctions are invisible here |
| Data Deficient | Insufficient information to assess | Absence of evidence, not evidence of safety |
| Not Evaluated | Has not been assessed against the criteria | Covers the large majority of described species |
IUCN Red List vs CITES: Direct Comparison Table
A common point of confusion for donors and researchers is the distinction between the IUCN Red List and CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora). While both aim to preserve biodiversity, their legal status, scope, and enforcement mechanisms are fundamentally different:
| Feature | IUCN Red List | CITES Appendices |
|---|---|---|
| Primary Authority | International Union for Conservation of Nature (Scientific Union) | United Nations Treaty (184 Signatory State Parties) |
| Core Purpose | Scientific assessment of global extinction risk | Regulating and restricting cross-border commercial wildlife trade |
| Legal Status | Informational science benchmark; non-binding | Legally binding international treaty on member nations |
| Classification System | 9 Categories (EX, EW, CR, EN, VU, NT, LC, DD, NE) | 3 Appendices (Appendix I Banned, Appendix II Regulated, Appendix III National) |
| Trade Enforcement | No trade bans or border enforcement powers | Strict customs export/import permits and international trade sanctions |
| Coverage Scope | Over 163,000 species evaluated across terrestrial & marine life | Over 40,900 animal and plant species traded internationally |
| Update Frequency | Continuous expert updates via Species Survival Commission | Amended every 2-3 years at Conferences of the Parties (CoP) |
Four common misreadings
Treating Least Concern as safe
The Red List assesses global extinction risk. A species can be secure globally and eliminated across an entire country, which matters enormously to the ecosystem in that country and not at all to the global category. Regional Red Lists exist for exactly this reason and are the correct reference for national conservation decisions.
Treating Data Deficient as low priority
Analyses of Data Deficient species have repeatedly suggested that a substantial share would qualify as threatened if assessed. The category correlates with being small, cryptic, hard to survey or living somewhere poorly studied — none of which are protective traits.
Confusing the Red List with CITES
CITES appendices regulate cross-border trade in specimens and are the product of negotiation between states. A species can be highly threatened and unlisted by CITES because it is not traded, or heavily traded and listed while not being globally threatened. Using one as evidence for the other is a category error that appears often in campaign material.
Ignoring the assessment date
Assessments are periodic and resource-limited. A category from ten years ago reflects the data available then, and for a rapidly declining species that gap can be the difference between two categories. The date is published alongside the assessment and is worth reading before quoting the category.
When a category improves — and what that actually indicates
Downlisting a species to a lower threat category is reported as a conservation success, and sometimes it is. But categories change for at least three distinct reasons, and only one of them is good news.
- Genuine improvement: the population has grown or stabilised because of intervention, and the improvement is attributable.
- Better data: the species was always more numerous than believed, and improved survey work corrected the estimate rather than the situation.
- Taxonomic change: a species has been split or merged, which redistributes populations across names and changes categories without any animal being affected.
The IUCN has developed a separate Green Status framework precisely because threat category is a poor measure of conservation success. A species can be stable at a small fraction of its former range and still be considered improved, which tells you something about risk and very little about recovery.
Not being about to go extinct is a low bar for calling something recovered.
The reasoning behind separating conservation success from extinction risk
How threat category maps onto funding decisions
| Situation | Typical funding reality | Why |
|---|---|---|
| Large, charismatic, Critically Endangered | Comparatively well funded | Fundraises easily; often has dedicated programmes |
| Small, uncharismatic, Critically Endangered | Severely underfunded | No public constituency, no appeal imagery |
| Vulnerable but declining fast | Underfunded | Prevention is cheaper and less urgent-sounding than rescue |
| Data Deficient | Almost unfunded | Cannot be fundraised for without a status to cite |
| Habitat itself | Chronically underfunded | Benefits many species and belongs to no single appeal |
The pattern is consistent: money follows recognisability, and recognisability is uncorrelated with either threat level or cost-effectiveness of intervention. A donor willing to fund the unglamorous end of this table is operating where the marginal value of a contribution is highest and the competition for funding is lowest.
Checking a conservation claim in three steps
- Look up the species assessment directlyThe Red List is public and searchable. The assessment page gives the category, the criteria met, the assessment year and the named assessors.
- Read the threats section, not the headlineAssessments list the specific pressures driving decline. If an appeal proposes an intervention that does not appear in that list, the mismatch is worth asking about.
- Check whether the geography matchesA global category attached to a project in one district tells you nothing about that district. Ask what the population there is doing and how it is monitored.
WildCare Trust works on endangered wildlife rescue and animal welfare through our wildlife rescue campaigns. For species-level field implementations, see our analysis on rhino conservation what works and the state of the world's migratory species report. We publish all field funding openly on our crypto donation transparency board.
Frequently asked questions
What are the 5 IUCN criteria for extinction risk?
The five quantitative IUCN criteria (A to E) used to assess extinction risk are: Criterion A (rate of population reduction), Criterion B (geographic range restriction and fragmentation), Criterion C (small population under 250 mature individuals and continuing decline), Criterion D (very small population under 50 individuals), and Criterion E (quantitative extinction probability of at least 50% within 10 years or 3 generations).
Which criterion decides a species extinction category?
Meeting any single criterion is sufficient. A species is classified in the highest threat category (Critically Endangered, Endangered, or Vulnerable) for which it meets any one of the five thresholds among Criteria A to E.
Is Critically Endangered the same as almost extinct?
Not exactly. It means the species meets defined quantitative thresholds for extremely high extinction risk, which can be triggered by a very small population, a very restricted range, or a very rapid decline. A species with tens of thousands of individuals can qualify if the decline is steep enough.
Why are common animals sometimes listed as threatened?
Because the criteria include rate of decline, not only absolute numbers. A species can still be widespread while losing a large share of its population within a few generations, and the framework is deliberately designed to flag that before the population becomes small.
What is the difference between the Red List and CITES?
The Red List assesses extinction risk on scientific criteria. CITES is a treaty regulating international trade, with appendices agreed between governments. A species can appear on one and not the other, and neither implies the other.
Should I avoid donating to work on Least Concern species?
No. Global category is a poor guide to local importance, ecological function or welfare need. Animal welfare work and local population recovery can be entirely worthwhile for species that are globally secure.
Why are so many species Not Evaluated?
Assessment requires expert time and data, both of which are scarce. Coverage is strong for mammals, birds and amphibians and thin for invertebrates, fungi and plants, which is where most described species actually are.