IUCN Red List Assessment

The IUCN Red List classifies species according to their risk of extinction in the wild. Assessors apply five standardized, quantitative criteria to evidence on population change, distribution, population size and modelled extinction probability; satisfying any one criterion can determine the extinction-risk category.

Evidence used in assessment

Assessors compile the best available information on the species across its range, including abundance, distribution, trends, habitat, threats and life history. Data may come from field surveys, monitoring, scientific literature, museum records, remote sensing and expert knowledge, with uncertainty documented rather than ignored.

• The assessment uses a defined time horizon, often linked to generation length, because population decline has different significance in short-lived and long-lived species.
• An assessment records its evidence, assumptions, geographic scope and justification, and is reviewed through the IUCN Red List process.

Five quantitative criteria

A species is tested against all applicable criteria. If it meets more than one category, the highest extinction-risk category supported by any criterion is assigned.

• Criterion A measures population reduction over a specified period.
• Criterion B examines restricted geographic range together with fragmentation, decline or extreme fluctuations.
• Criterion C considers a small population that is continuing to decline.
• Criterion D covers very small or geographically restricted populations.
• Criterion E uses quantitative analysis, such as population viability analysis, to estimate extinction probability.

Resulting categories and interpretation

The assessed categories are Least Concern, Near Threatened, Vulnerable, Endangered, Critically Endangered, Extinct in the Wild and Extinct. Vulnerable, Endangered and Critically Endangered collectively constitute the threatened categories.

• Data Deficient means that available information is inadequate for assessing risk; it does not mean that the species is safe or threatened.
• Not Evaluated means that the species has not yet been assessed against the criteria.
• Red List status measures biological extinction risk; it does not by itself create legal protection or prescribe a particular conservation action.

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