US President Donald Trump's administration on Monday finalized rollbacks to key provisions of the Endangered Species Act, a law supported by a large majority of Americans and credited with saving the gray wolf, bald eagle and grizzly bear.

This fearsome fox sent a troublesome badger packing when it threatened her cubs - by biting its face and tearing out chunks of its fur. (Photo: VCG)

The move was met with anger by environmental groups and Democratic politicians, including presidential candidate Joe Biden, while two states announced they would take legal action.

Amendments include removing a rule that automatically conveys the same protections to threatened species and endangered species, and allowing information on economic impact to be gathered when making determinations on how wildlife is listed.

In a statement characterizing the changes as "improvements," Interior Secretary David Bernhardt said: "The best way to uphold the Endangered Species Act is to do everything we can to ensure it remains effective in achieving its ultimate goal -- recovery of our rarest species.

"An effectively administered Act ensures more resources can go where they will do the most good: on-the-ground conservation," added the former oil and gas lobbyist.

Biden, the leading contender for the Democratic party's nomination in next year's presidential election, hit back, saying the amendments could push some species toward oblivion.

"For decades, the Endangered Species Act has protected our most vulnerable wildlife from extinction. Now, President Trump wants to throw it all away," he tweeted.

"At a time when climate change is pushing our planet to the brink, we should strengthen protections -- not weaken them."

He was joined in his criticism by Democratic Senator Dianne Feinstein of California, whose state is home to 296 protected plant and animal species. 

Conservation groups also reacted with dismay, vowing legal challenges against what the nonprofit Sierra Club dubbed the "Trump Extinction plan."

Kristen Boyles, an attorney for Earthjustice, told AFP: "Prior to today, a newly-listed threatened species would immediately have protections in place, there was sort of a default rule." 

But "a species could be listed right now and it would have no further protections than it did before it was listed under the act" until a species-specific review takes place, she added, and even then it was not clear how robust those protections would be.