The Trump administration's changes to the Endangered Species Act could threaten efforts to preserve the monarch butterfly and other struggling species that haven't yet been officially labeled "endangered," experts and advocates say.

Critics told The Associated Press and the BBC that the changes to the decades-old policy announced Monday by the Trump administration could affect conservation efforts involving the butterfly, which migrates annually between Mexico and Canada.

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Along with a new provision that allows the administration to assign costs to preserving individual species, the changes end blanket policies protecting all species designated as "threatened" in favor of individual plans for each species developed on a case-by-case basis. Other changes also force the federal government to deal with threats to species only in the "foreseeable" future, a change which some argue eliminates climate change as a factor that agencies can consider.

The monarch, considered threatened by many scientists, is currently under review by the U.S. Fish and Wildlife Service to determine its designation under the act. A decision in the matter is expected before the end of 2020.

Critics of the Trump administration's plan warned that the new changes will remove some crucial protections for threatened species and slow-walk the process of determining whether a species is threatened.

"These changes crash a bulldozer through the Endangered Species Act's lifesaving protections for America's most vulnerable wildlife," Noah Greenwald, endangered species director at the Center for Biological Diversity, told the BBC.

"For animals like wolverines and monarch butterflies, this could be the beginning of the end," he added.

Karen Oberhauser, director of the arboretum at the University of Wisconsin, told the AP that monarchs are such a visible species that a decline in the population should serve as a warning to conservationists and the federal government.

“One of the reasons I think it’s so important to focus on monarch conservation is monarchs connect people to nature,” Oberhauser told the AP. “They’re beautiful, they’re impressive, people have seen them since we were children.”

“If the changes that humans are causing are leading to the decline of species that are as common as the monarchs, it’s scary,” she added. “The environment is changing such a lot that monarchs are declining. And I think that doesn’t bode well for humans.”

Interior Secretary David Bernhardt argued Monday that the Trump administration's changes would merely streamline the Endangered Species Act and allow for resources to be spent wisely.

“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,” he said in a press release. “An effectively administered Act ensures more resources can go where they will do the most good: on-the-ground conservation.”