An endangered species is one at serious risk of extinction. The International Union for Conservation of Nature maintains the Red List, the global authority on species status. Categories range from least concern to extinct. Endangered sits near the top. Critically endangered is worse.

Species become endangered for several reasons. Habitat loss is the biggest. Poaching, pollution, disease, and climate change add pressure. Small populations are especially vulnerable. Inbreeding weakens them. A single disaster can wipe them out. The vaquita, a small porpoise in the Gulf of California, numbers fewer than 20. The Javan rhino has about 75 individuals left.

Protection works when it is enforced. Bald eagles recovered after DDT was banned. Mountain gorillas have slowly increased with intensive protection. China's giant panda was downgraded from endangered to vulnerable in 2016. Success requires habitat, funding, and political will. Failure is permanent.

Key threats

• Habitat loss
• Poaching and wildlife trade
• Pollution
• Climate change
• Invasive species