A legal petition was filed this week calling on the U.S. Fish and Wildlife Service to expand its plans for recovering grizzly bears.

The petition was filed by the Center for Biological Diversity.

The plan includes returning the animals to vast portions of the American West, like Gila/Mogollon complex in Arizona and New Mexico, Utah's Uinta Mountains, California's Sierra Nevada and the Grand Canyon in Arizona.

Getting the bears back to some or all of these locations is an important step toward recovering them under the Endangered Species Act. It could also potentially triple the grizzly bear population in the lower 48, from a meager 1,500 to 1,800 today to as many as 6,000, according to a release by the Center for Biology Diversity.

"Grizzly bears are one of the true icons of the American West, yet today they live in a paltry 4 percent of the lands where they used to roam," said Noah Greenwald, the Center's endangered species director, according to the release. "We shouldn't be closing the book on grizzly recovery but beginning a new chapter - one where these amazing animals live wherever there's good habitat for them across the West."

The petition calls on the Service to revise its 1993 recovery plan to include include suitable grizzly habitat across the West and to incorporate the findings of recent research that raises questions about the long-term viability of current grizzly bear populations.

Bear populations are in trouble due to climate change, human population growth, invasive species, among other factors.

Grizzly bears have been listed as a threatened species under the Endangered Species Act since 1975. Since then the Service has looked for a fragmented approach to recovery that fails to meet the intention of the act to recover species across "significant portions of their historic range," according to the release.

The agency has created recovery strategies for six populations, including: the Greater Yellowstone, Northern Continental Divide centered on Glacier National Park, Cabinet-Yaak, Selkirk Mountains, North Cascades and Selway-Bitterroot.

The agency has only carried out on-the-ground recovery efforts for the first four populations however.

"The good news is that with the safety net of the Endangered Species Act, the health of Yellowstone and Glacier area grizzly bears has improved - but it's way too early to declare victory and walk away," Greenwald said. "All remaining populations are isolated, especially Yellowstone. Yet the science is clear that, if we're serious about recovering grizzly bears, we need more populations around the West, and more connections between them, so they don't fall prey to inbreeding and so they have a chance of adapting to a warming world. If we want these incredible bears around for centuries to come, we've still got a lot of work left to do."

Click here to see an infographic on grizzly bears in the West.

A grizzly bear recovery plan that meets the requirements of the Endangered Species Act would establish specific landscape-wide population recovery targets capable of sustaining the species, according to the release.

The plan would also protect the bear's habitat holistically.

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