Who declares an animal extinct?

The International Union for Conservation of Nature (IUCN) is the international authority on the conservation status of species. IUCN's Red List of Threatened Species™ provides taxonomic, conservation status and distribution information on taxa that have been evaluated using IUCN criteria. Species are assigned to one of eight Red List categories: Least Concern (LC), Near Threatened (NT), Vulnerable (VU), Endangered (EN), Critically Endangered (CR), Extinct in the Wild (EW), Extinct (EX), and Data Deficient (DD).

If a species is declared Extinct (EX) it means that there is no reasonable doubt that the last individual has died. Species become extinct when they can no longer sustain themselves in sufficient numbers to avoid extinction. This can be due to a variety of factors, including habitat loss, hunting, climate change, disease, and more.