IUCN Red List

The International Union for Conservation of Nature maintains the Red List, a system it intends to be easily and widely understood for classifying species at high risk of global extinction. The point a reader most needs is that its category names are not loose descriptions. They are rungs on one defined scale, and a species is placed on it by assessment against published criteria covering population size, rate of decline, geographic range and similar measures.

There are nine categories. Three describe threatened species: Critically Endangered, Endangered and Vulnerable, in decreasing order of risk. Near Threatened sits just below them, for a species close to qualifying but not yet there, and Least Concern is the lowest risk. Extinct in the Wild and Extinct sit above. Two more, Data Deficient and Not Evaluated, record that no judgement has been reached rather than that a species is safe.

So a headline saying a species is no longer endangered is usually reporting a move between two of these rungs, not a declaration of safety. The scale measures extinction risk and nothing else. A species can move down it while remaining rare, confined to a small area, or wholly dependent on the conservation work that improved its position in the first place.