IUCN - Critically Endangered risk category

Critically endangered is the highest risk category assigned by the IUCN (International Union for Conservation of Nature) Red List to wild species. There are five quantitative criteria to determine whether a taxon is threatened.

A taxon is critically endangered when the best availabile evidence indicates that it meets any of the following criteria:

1. Populations have declined or will decrease, by greater than 80% over the last 10 years or three generations.
2. Have a restricted geographical range.
3. Small population size of less than 250 individuals and continuing decline at 25% in 3 years or one generation.
4. Very small or restricted population of fewer than 50 mature individuals.
5. High probability of extinction in the wild.