The Criteria for Critically Endangered (CR)
(2001 IUCN Red List Categories and Criteria version 3.1)

A taxon is Critically Endangered when the best available evidence indicates that it meets any of the following criteria (A to E), and it is therefore considered to be facing an extremely high risk of extinction in the wild:

A. Reduction in population size based on any of the following:

  1. An observed, estimated, inferred or suspected population size reduction of ≥ 90% over the last 10 years or three generations, whichever is the longer, where the causes of the reduction are clearly reversible AND understood AND ceased, based on (and specifying) any of the following:
    • direct observation
    • an index of abundance appropriate to the taxon
    • a decline in area of occupancy, extent of occurrence and/or quality of habitat
    • actual or potential levels of exploitation
    • the effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.
  2. An observed, estimated, inferred or suspected population size reduction of ≥ 80% over the last 10 years or three generations, whichever is the longer, where the reduction or its causes may not have ceased OR may not be understood OR may not be reversible, based on (and specifying) any of the following:
    • direct observation
    • an index of abundance appropriate to the taxon
    • a decline in area of occupancy, extent of occurrence and/or quality of habitat
    • actual or potential levels of exploitation
    • the effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.
  3. A population size reduction of ≥ 80%, projected or suspected to be met within the next 10 years or three generations, whichever is the longer (up to a maximum of 100 years), based on (and specifying) any of the following:
    • an index of abundance appropriate to the taxon
    • a decline in area of occupancy, extent of occurrence and/or quality of habitat
    • actual or potential levels of exploitation
    • the effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.
  4. An observed, estimated, inferred, projected or suspected population size reduction of ≥ 80% over any 10 year or three generation period, whichever is longer (up to a maximum of 100 years in the future), where the time period must include both the past and the future, and where the reduction or its causes may not have ceased OR may not be understood OR may not be reversible, based on (and specifying) any of the following:
    • direct observation
    • an index of abundance appropriate to the taxon
    • a decline in area of occupancy, extent of occurrence and/or quality of habitat
    • actual or potential levels of exploitation
    • the effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.

B. Geographic range in the form of either B1 (extent of occurrence) OR B2 (area of occupancy) OR both:

  1. Extent of occurrence estimated to be less than 100 km2, and estimates indicating at least two of a-c:
    1. Severely fragmented or known to exist at only a single location.
    2. Continuing decline, observed, inferred or projected, in any of the following:
      • extent of occurrence
      • area of occupancy
      • area, extent and/or quality of habitat
      • number of locations or subpopulations
      • number of mature individuals.
    3. Extreme fluctuations in any of the following:
      • extent of occurrence
      • area of occupancy
      • number of locations or subpopulations
      • number of mature individuals.
  2. Area of occupancy estimated to be less than 10 km2, and estimates indicating at least two of a-c:
    1. Severely fragmented or known to exist at only a single location.
    2. Continuing decline, observed, inferred or projected, in any of the following:
      • extent of occurrence
      • area of occupancy
      • area, extent and/or quality of habitat
      • number of locations or subpopulations
      • number of mature individuals.
    3. Extreme fluctuations in any of the following:
      • extent of occurrence
      • area of occupancy
      • number of locations or subpopulations
      • number of mature individuals.

C. Population size estimated to number fewer than 250 mature individuals and either:

  1. An estimated continuing decline of at least 25% within three years or one generation, whichever is longer, (up to a maximum of 100 years in the future) OR
  2. A continuing decline, observed, projected, or inferred, in numbers of mature individuals AND at least one of the following (a-b):
    1. Population structure in the form of one of the following:
    2. no subpopulation estimated to contain more than 50 mature individuals, OR
    3. at least 90% of mature individuals in one subpopulation.
  3. Extreme fluctuations in number of mature individuals.

D. Population size estimated to number fewer than 50 mature individuals.

E. Quantitative analysis showing the probability of extinction in the wild is at least 50% within 10 years or three generations, whichever is the longer (up to a maximum of 100 years).

Reference: IUCN. (2012). IUCN Red List Categories and Criteria: Version 3.1. Second edition. Gland, Switzerland and Cambridge, UK: IUCN. iv + 32pp.
Link: http://jr.iucnredlist.org/documents/redlist_cats_crit_en.pdf