IUCN criteria and categories

CRITERION A. Decrease of the size of the population

Main criterion Subcriterion Definition Formula
90 % or a larger decrease of the size of the population for the last 10 years or for 3 generations (CR) 70 % or a larger decrease of the size of the population for the last 10 years or for 3 generations (EN) 50 % or a larger decrease of the size of the population for the last 10 years or for 3 generations (VU) 1. Decline in the past (observed, estimated, understood or supposed) when the reasons for that are clearly reversible and understandable and discontinued, based on any of the following: a. direct observation A1a
b. index of abundance A1b
c. decrease of the occupied area, the size of the distribution and/or quality of the habitat A1c
d. existing or potential level of use (exploitation) A1d
e. influence of introduced species, hybridization, pathogens, pollutants, competition or parasites A1e
80 % or a larger decrease of the size of the population for the last 10 years or for 3 generations (CR) 50 % or a larger decrease of the size of the population for the last 10 years or for 3 generations (EN) 30 % or a larger decrease of the size of the population for the last 10 years or for 3 generations (VU) 2. Decline in the past (observed, estimated, understood or supposed) when the decline or the reasons for it may be not reversible or may be incomprehensible or may be not discontinued, based on any of the following: a. direct observation A2a
b. index of abundance A2b
c. decrease of the occupied area, size of distribution and/or the quality of the habitat A2c
d. existing or potential level of use (exploitation) A2d
e. influence of introduced species, hybridization, pathogens, pollutants, competition or parasites A2e
80 % or a larger decrease of the size of the population for the last 10 years or for 3 generations (maximum up to 100 years in the future) (CR) 50 % or a larger decrease of the size of the population for the last 10 years or for 3 generations (maximum up to 100 years in the future) (EN) 30 % or a larger decrease of the size of the population for the last 10 years or for 3 generations (a maximum of up to 100 years in the future) (VU) 3. Decline in the future (assumed or supposed), based on any of the following: a. direct observation A3a
b. index of abundance A3b
c. decrease of the occupied area, size of distribution and/or the quality of the habitat A3c
d. existing or potential level of use (exploitation) A3d
e. influence of introduced species, hybridization, pathogens, pollutants, competition or parasites A3e
80 % or a larger decrease of the size of the population for the last 10 years or for 3 generations (a maximum of up to 100 years in the future) (CR) 50 % or a larger decrease of the size of the population for the last 10 years or for 3 generations (a maximum of up to 100 years in the future) (EN) 30 % or a larger decrease of the size of the population for the last 10 years or for 3 generations (a maximum of up to 100 years in the future) (VU) 4. The decline may include both the past and the future (observed, estimated, understood, assumed or supposed) when the decline or the reasons for it may not be reversible or may not be understandable or may not be discontinued, based on any of the following: a. direct observation A4a
b. index of abundance A4b
c. decrease of the occupied area, size of distribution and/or the quality of the habitat A4c
d. existing or potential level of use (exploitation) A4d
e. influence of introduced species, hybridization, pathogens, pollutants, competition or parasites A4e

CRITERION B. SMALL REGION OF DISTRIBUTION, fragmentation, decline or fluctuating

Major criterion Subcriterion Definition Formula
1. The region of distribution is estimated at <100 sq. km (CR) and at least two of the indicators a, b or c are present The region of distribution is estimated at <5000 sq. km (EN) and at least two of the indicators a, b or c are present The region of distribution is estimated at <20000 sq. km (VU) and at least two of the indicators a, b or c are present a. The region of distribution is strongly fragmented or is found: in one habitat (CR)
in ≤ 5 habitats (EN)
in ≤ 10 habitats (VU)
None B1a
b. Continuing decline (observed, understood or assumed, on any of the following: i. region of distribution B1bi
ii. occupied area B1bii
iii. the area, the scope and/or quality of the habitat B1biii
iv. the number of habitats or subpopulations B1biv
v. the number of adult individuals B1bv
c. Extreme fluctuations of any of the following: i. region of distribution B1ci
ii. the occupied area B1cii
iii. the number of habitats or subpopulations B1ciii
iv. the number of adult individuals B1civ
2. The area occupied is estimated at less than 10 sq. km (CR) and the estimate shows that at least two of a-с are met: The area occupied is estimated at less than 500 sq. km (EN) and the estimate shows that at least two of a-с are met: The area occupied is estimated at less than 2000 sq. km (VU) and the estimate shows that at least two of a-с are met: a. The region of distribution is strongly fragmented
or is found:
in one habitat (CR)
in ≤ 5 habitats (EN)
in ≤ 10 habitats (VU)
None B2a
b. Continuing decline (observed, understood or assumed, on any of the following: i. region of distribution B2bi
ii. occupied area B2bii
iii. the area, the scope and/or the quality of the habitat B2biii
iv. the number of habitats or subpopulations B2biv
v. the number of adult individuals B2bv
c. Extreme fluctuations of any of the following: i. region of distribution B2ci
ii. occupied area B2cii
iii. the number of habitats or subpopulations B2ciii
iv. the number of adult individuals B2civ

CRITERION С. SMALL POPULATIONS declining or fluctuating

Major criterion Subcriterion Definition Formula
The size of the population is estimated at less than 250 adult individuals (CR) and/or: The size of the population is estimated at less than 2500 adult individuals (EN) and/or: The size of the population is estimated at less than 10000 adult individuals (VU) and/or: 1. Estimated is a continuing decline of ≥ 25 % within 3 years or 1 generation (CR), maximum up to 100 years in the future
Estimated is a continuing decline of ≥ 20 % within 5 years or 2 generations (EN), maximum up to 100 years in the future
Estimated is a continuing decline of ≥ 10 % within 10 years or 3 generations (VU), maximum up to 100 years in the future
None C1
2. Continuing decline (estimated, assumed or understood) of the number of adult individuals and at least one of the following (a-b) is present: ai. all subpopulations ≤ 50 (CR)
all subpopulations ≤ 250 (EN)
all subpopulations ≤ 1000 (VU)
C2ai
aii. ≥ 90% adult individuals are in one subpopulation (CR)
≥ 90% of the adult individuals are in one subpopulation (EN)
all adult individuals are in one subpopulation (VU)
C2aii
b. Extreme fluctuations in the numbers of adult individuals C2b

CRITERION D1. Very small populations

The size of the population is estimated at less than 50 adult individuals The size of the population is estimated at less than 250 adult individuals The size of the population is estimated at less than 1000 adult individuals None None D1

CRITERION D2. Very small area of distribution

The area occupied is estimated at less than 20 sq. km. or typically occupied habitats are less than 6 (only VU – capable of becoming CR or EX within a very short time) None None D2

CRITERION E. Quantitative analyses

20 % probability of extinction in nature in the following 20 years or five generations (EN), whichever of the two is longer (a maximum of up to 100 years) 10 % probability of extinction in nature during the next 100 years (VU)     E