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In the Cascade Range in Washington, hotter summers and rainy winters are robbing the Mt. Rainier White-tailed Ptarmigan of the alpine snow it relies on year-round. On the East Coast, rising seas are gobbling up the wetland habitat of Saltmarsh Sparrows. And on the Hawaiian Islands, forest birds like the ‘I‘iwi are being chased uphill as warming temperatures allow mosquitoes—and the deadly avian malaria they carry—to expand into higher elevations.

These and other imperiled birds, the U.S. Fish and Wildlife Service (FWS) says, help to underscore the need for a proposed policy change that would allow wildlife managers to establish “experimental populations” of threatened or endangered species in areas where they’ve never lived before. The Endangered Species Act (ESA) typically allows these introductions outside of where a species currently lives, but only within its historical range. But climate change is already forcing species to pull up stakes, the FWS says, so the new policy would enable the agency to greenlight introductions of listed species into new habitats.

“Recovering species and preventing their extinction will require innovative, proactive, science-based policies and conservation actions that address the growing impacts from climate change and invasive species before it is too late,” said Martha Williams, FWS director, announcing the proposal. The agency will accept comments from the public until August 8 before writing a final rule.

Scientists and ESA experts tell ���Ϲ��� that the proposed change would give wildlife managers the necessary flexibility to preserve vulnerable species in a worsening climate crisis. “It’s the type of bold thinking that we really need to mitigate threats,” says Michael Scott, a retired conservation biologist from the University of Idaho. “It could become a major tool with climate change.”

The new policy would provide “a useful tool and a necessary tool,” says Patrick Parenteau, a Vermont Law School professor, of the proposed change. “We have to do some things we’ve never done before to deal with the threats of climate, which we’ve never seen before.”

Others warn, however, that the plan could have unintended consequences for ecosystems. “I think it’s potentially disastrous,” says Daniel Simberloff, an ecologist at University of Tennessee, Knoxville. He and his colleague Anthony Ricciardi, an invasion biologist at McGill University, have that introducing a species outside of its historical range—assisted colonization or assisted migration, as scientists often refer to it—poses many risks.

Introduced animals could compete with native ones for food, for instance. If not appropriately quarantined, they could carry hitchhiking insects or pathogens into the ecosystem. “All you’re doing is ecological gambling,” Ricciardi says. “You spin the roulette wheel enough times, and you’ll get some disasters.” 

The introduction of red squirrels to Newfoundland is one such example, Ricciardi says. as prey to boost the declining pine marten population, the red squirrels began to compete with native Red Crossbills for black spruce seeds,. Native species like the Red Crossbill evolved over millennia in their particular environments, making it difficult to fully understand how they might perform when a novel animal is introduced, even after years of extensive research and planning.

But taking such gambles may be necessary on a quickly warming planet, others argue. “The theme is one that’s going to be important for a lot of Endangered Species Act programs, and that is that climate change is transforming ecosystems in ways that could make areas outside current and even historical range of a species—and even areas that would not currently be occupiable—occupiable,” says J.B. Ruhl, an environmental law expert at Vanderbilt University.

Aligning with that thinking, the Biden administration announced on Thursday that it is scrapping a Trump-era definition of the word “habitat” under the ESA. That narrow interpretation made it harder to protect places not currently occupied by a species that climate change could render suitable, or that could be restored to provide habitat. “The growing extinction crisis highlights the importance of the Endangered Species Act and efforts to conserve species before declines become irreversible,” said Shannon Estenoz, the Interior Department’s assistant secretary for fish and wildlife and parks, . “Today’s action will bring implementation of the Act back into alignment with its original purpose and intent.”

Several endangered birds have already benefited from the current policy for experimental populations, including Whooping Cranes, Guam Rails, and California Condors. Lead poisoning and other hazards reduced the condor to a small,  in the 1980s. But that group of breeders became the source of two experimental populations in the western United States, including a new one in May managed by the Yurok Tribe in northern California. Thanks to these experimental populations, now more than 300 adult California Condors soar free. 

The revised policy could help other avian species find similar success outside their historical range. “I do think it allows us to move the needle when it comes to our conservation actions,” says Brooke Bateman, the ���Ϲ���’s director of climate science. Bateman cites rosy-finches as potential beneficiaries of the change. North America’s three species—Black, Brown-capped, and Gray-crowned Rosy-Finches—summer at high elevations around remnant snowfields, which will shrink with rising temperatures. The birds aren’t listed under the ESA, but marooned on these isolated mountaintops, similar to island species that have few nearby habitats to migrate to, much of their current range will disappear. Relocating them to more northern Rocky Mountain peaks that remain cooler could become necessary to save the species. “It’s going to be an interesting future to see how this plays out,” Bateman says.

Should the FWS finalize and implement the proposed change, it’s crucial that the government not give up on protecting existing habitat as it considers transplanting species to a new territory, multiple experts tell ���Ϲ���. “Be cautious about abandoning historic habitat and throwing in the towel,” says John Morton, a retired FWS biologist. Assisted migration may be a new fact of life on a changing planet, he says, but it should be the last resort.