An endangered species is any plant or animal at serious risk of disappearing from Earth entirely. The term has both a general meaning and a precise legal one: globally, the International Union for Conservation of Nature (IUCN) maintains a list of species in trouble, while in the United States the Endangered Species Act (ESA) gives certain species federal legal protection. As of 2025, scientists have assessed over 172,000 species worldwide, and roughly 48,600 of them are threatened with extinction.
How “Endangered” Differs From “Threatened”
Under the ESA, species fall into two categories. An endangered species is one currently in danger of extinction throughout all or a significant portion of its range. A threatened species is one likely to become endangered in the foreseeable future. The distinction matters because it determines how much legal protection a species receives, what activities are restricted near its habitat, and how much funding goes toward recovery efforts.
The IUCN uses a more detailed scale. Its Red List ranks species across several categories, from “Least Concern” all the way up to “Critically Endangered” and finally “Extinct.” When news outlets report that a species is “threatened with extinction,” they’re typically combining three IUCN categories: Vulnerable, Endangered, and Critically Endangered.
Why Species Become Endangered
The single biggest driver of biodiversity loss worldwide is habitat destruction through changes in land and sea use. When forests are cleared for agriculture, wetlands are drained for development, or coral reefs are degraded by warming oceans, the species that depend on those ecosystems lose the resources they need to survive and reproduce.
Direct exploitation of natural resources ranks second. This includes overhunting, overfishing, and illegal wildlife trade. Pollution comes in third. Climate change and invasive species, while increasingly significant, have so far been less dominant than habitat loss and exploitation as direct drivers of species decline, though their impact is accelerating.
The U.S. Fish and Wildlife Service uses five specific factors when deciding whether a species needs protection:
- Habitat loss: the present or threatened destruction of the species’ habitat or range
- Overuse: commercial, recreational, or scientific exploitation
- Disease or predation: threats from illness or other species
- Regulatory gaps: existing laws that fail to adequately protect the species
- Other threats: any additional natural or human-caused factors affecting survival
A species only needs to meet one of these criteria to qualify for listing.
How a Species Gets Legal Protection
In the United States, any person or organization can petition the Fish and Wildlife Service to protect a species. The process follows a set timeline. Within 90 days of receiving a petition, the agency must determine whether there is substantial information suggesting the species may need protection. If that initial review is positive, a full status review follows.
Within one year of receiving the petition, the agency must decide whether listing is warranted. If it is, a proposed rule is published in the Federal Register, followed by a 60-day public comment period and independent peer review from species specialists. After incorporating feedback, the agency publishes a final rule, and the species is officially added to the endangered or threatened list 30 days later.
Sometimes a species clearly qualifies but the agency lacks the resources to act immediately. In those cases, the species is labeled “warranted but precluded” and placed on a candidate list. It stays there, with annual re-evaluation, until the agency can move forward with a formal proposal.
What Happens After a Species Is Listed
Once listed, a species gains significant legal protections. It becomes illegal to “take” an endangered animal, which under the ESA means harassing, harming, pursuing, hunting, shooting, wounding, killing, trapping, capturing, or collecting it. Federal agencies must ensure that any project they fund or authorize does not jeopardize the species’ continued existence or destroy its critical habitat.
Recovery plans are developed outlining the specific steps needed to rebuild the population. These plans often combine two broad approaches to conservation. The primary strategy is protecting and restoring the species in its natural habitat, allowing populations to recover while still experiencing normal evolutionary pressures like natural selection and genetic mixing. For species that are extremely rare or scattered, a second approach becomes essential: maintaining populations outside their natural habitat through captive breeding programs, seed banks, or managed reserves. The most effective recovery efforts use both strategies together, breeding individuals in controlled settings and reintroducing them into restored wild habitats.
The Economic Value of Protection
Protecting endangered species isn’t only a moral or ecological concern. These species often underpin industries and ecosystem services worth billions. NOAA Fisheries estimates that Americans are willing to pay $4.38 billion annually for the recovery of the endangered North Atlantic right whale alone. That same species generated an estimated $2.3 billion in sales through whale watching tourism and related economic activity.
Beyond direct tourism dollars, healthy ecosystems with intact species populations provide services that are expensive or impossible to replicate artificially. Pollinating insects support agriculture. Predators keep prey populations in check, preventing overgrazing. Wetland species filter water naturally. When key species disappear, these services degrade, and the economic costs can be enormous.
The Global Picture in 2025
The IUCN Red List, updated at the 2025 World Conservation Congress in Abu Dhabi, now tracks 172,620 species. Of those, 48,646 are threatened with extinction. That number has climbed steadily as scientists assess more species and as threats intensify. Recent updates flagged Arctic seals as newly threatened by climate change and documented ongoing declines in bird populations worldwide.
These numbers almost certainly undercount the true scale of the problem. The vast majority of insects, fungi, and deep-sea organisms have never been formally assessed. The species we know are in trouble represent a fraction of those that actually are.