Table 1

Simplified overview of thresholds for the IUCN Red List criteria.

criterioncritically endangeredendangeredvulnerablequalifiers and notes
A1: reduction in population size≥90%≥70%≥50%over 10 years/3 generations in the past, where causes are reversible, understood and have ceased
A2–4: reduction in population size≥80%≥50%≥30%over 10 years/3 generations in past, future or combination
B1: small range (extent of occurrence)<100 km2<5000 km2<20 000 km2plus two of (a) severe fragmentation/few localities (1, ≤5, ≤10), (b) continuing decline, (c) extreme fluctuation
B2: small range (area of occupancy)<10 km2<500 km2<2000 km2plus two of (a) severe fragmentation/few localities (1, ≤5, ≤10), (b) continuing decline, (c) extreme fluctuation
C: small and declining population<250<2500<10 000mature individuals. Continuing decline either (1) over specified rates and time periods or (2) with (a) specified population structure or (b) extreme fluctuation
D1: very small population<50<250<1000mature individuals
D2: very small rangeN/AN/A<20 km2 or ≤5 locationscapable of becoming critically endangered or extinct within a very short time
E: quantitative analysis≥50% in 10 years/3 generations≥20% in 20 years/5 generations≥10% in 100 yearsestimated extinction-risk using quantitative models, e.g. population viability analyses