What makes a creature a vulnerable species? What makes it endangered? Scientists at the International Union for the Conservation of Nature (IUCN) use these criteria to group animal populations worldwide.

criteria
Plural Noun

set of standards or rules.

endanger
Verb

to put at risk.

Noun

organism threatened with extinction.

International Union for the Conservation of Nature (IUCN)
Noun

environmental organization concerned with preserving natural ecosystems and habitats.

population
Noun

total number of people or organisms in a particular area.

scientist
Noun

person who studies a specific type of knowledge using the scientific method.

vulnerable species
Noun

level of conservation between "near threatened" and "endangered." Vulnerable is the lowest of the "threatened" categories.