How does the Endangered Species Act protect animals at risk?

The United States’s Endangered Species Act (ESA), signed into law in 1973, has helped revive the populations of nearly 300 species. 

The ESA protects animals that are classified under federal law as “endangered”—at risk of going extinct—and “threatened”—at risk of being endangered. 

2023 marks the ESA’s 50th anniversary. In half a century, the law has created legal pathways for federal and local governments to work together to save species such as the bald eagle, the American alligator, the Florida manatee, and the peregrine falcon. 

Most recently, the wolverine, a type of weasel, was added to the ESA because its existence is threatened by climate change and the loss of its habitat.

Here’s how the ESA works, and why conservationists say it’s more important than ever.  

How endangered species are protected

The U.S. Fish and Wildlife Service and the National Marine Fisheries Service are the two government agencies primarily responsible for implementing the ESA. 

To award a species ESA protection, these agencies take into consideration destruction to a species’ habitat, whether it has been over-consumed, threats from disease or predation, whether human actions put it in danger, and any policies currently protecting it. 

A federally protected species is typically listed with a “critical habitat” designation that outlines where ecosystems should be left untouched. The law also requires a research and management plan be formed to monitor a species’ population. 

It is illegal under the ESA to capture, hunt, shoot, or otherwise harm an animal that’s listed as endangered or threatened.

Conservation successes

Bald eagles are a poster child for the ESA and just one of the species to have seen tremendous population growth through conservation. In the 1960s, only about 500 bald eagles existed in the continental U.S. The birds ate fish infected with the pesticide DDT that was found in waterways. This chemical interfered with their ability to produce eggshells strong enough to hatch their young.

Captive breeding programs, habitat protection, and a ban on DDT helped restore bald eagle populations. Today, the U.S. Fish and Wildlife Service estimates more than 300,000 bald eagles live in the U.S.

The ESA also played a critical role in restoring populations of American alligators. After facing threats to their habitat and being excessively hunted, there only an estimated 100,000 individuals thought to exist across the South. Today, there are over a million, and the alligator was removed from the endangered species list in 1987.

Some species status on the endangered species list is unclear—as populations rebound, many are facing intensifying threats from habitat loss or climate change.

The whooping crane, North America’s tallest bird, can only be found in the U.S and Canada. It's thought 10,000 once existed in a habitat that spanned from the Great Plains to the Gulf Coast. In 1941, just 21 cranes were still alive. Today, the population is over 500 and listed as endangered, but scientists are debating whether it should be reclassified as threatened, a move that would loosen restrictions on habitats some scientists argue are increasingly at risk.

Conservation challenges

Critics have argued that the act is expensive and ineffective because it protects over 1,300 species. Several federal courts have heard and rejected arguments that the ESA is unconstitutional. Members of Congress have tried to weaken the law, and spending cuts to federal agencies have limited how effectively scientists can monitor species’ health.

In October 2023, the U.S. Fish and Wildlife Service officially removed 21 species from the ESA, saying they were likely extinct. Many had been added to the endangered species list in 1973 and may have already been extinct at the time they were listed. 

One species, the ivory-billed woodpecker, was last seen in 1944 but remains a hotly debated scientific mystery. Initially considered for delisting, the bird remains on the list as scientists continue to debate its survival. 

The ESA remains critical for protecting endangered species. Studies show the rate of extinction is increasing around the world. Nearly a third of plants and 40 percent of animals in the U.S. are existentially threatened, according to research done by the environmental group NatureServe.

In a press release announcing the 21 presumed extinct species, the U.S. Fish and Wildlife Service highlighted the important role the ESA plays of protecting species "before declines become irreversible."