DENVER — Gray wolves howled across the land now known as Colorado for millennia before they were hunted out of existence. Now state residents are deciding whether to let the predators once again lift their voices in the southern Rockies.

If approved, a precedent-setting ballot measure would require state biologists to reintroduce the native carnivores to more than 17 million acres of rugged public lands in Colorado’s rural west by the end of 2023.

The proposal is the capstone of a 40-year campaign by conservationists to return the animals to their former range along the Rocky Mountain chain from Canada to Mexico. And it could herald a paradigm shift in wildlife management, backers say, by giving Coloradans the nation’s first vote on reintroducing an endangered species to a place it once thrived — a decision typically reserved for government scientists.

Whatever the outcome, the debate in Colorado, where early voting began this month, is already focusing on a thornier question that follows wolves wherever they roam: Can people coexist with them?

“Make no mistake, putting wolves on the ground in Colorado is as much a social change movement as it is an environmental movement,” said Rob Edward, a Boulder-based business analyst heading the wolf reintroduction effort. “What we are asking people to do is look back on their ancestors’ actions and say, ‘That really wasn’t the right move to eradicate wolves.’”

Gray wolves flourished in North America before European settlers arrived. But by the 1930s, they had been trapped, poisoned and shot nearly to extinction in the Lower 48. Most gray wolves were listed as endangered by the mid-1970s, with small populations remaining along the Canadian border.

The federal government reintroduced several dozen gray wolves to Yellowstone National Park and Idaho in 1995. Today, about 1,700 live in Washington, Oregon, Idaho, Utah, Montana and Wyoming, representing what the U.S. Fish and Wildlife Service has hailed as “one of the greatest comebacks for an animal in U.S. conservation history.”

The agency has repeatedly removed and returned federal protections for wolf populations in various states in recent decades amid controversy and lawsuits. In 2019, the agency proposed removing all gray wolves in the Lower 48 from the endangered species list, and the Trump administration has vowed to make that happen this year.

But wolves’ success stories have also been marred by conflict with ranchers, whose livestock make easy prey. In Washington state, wildlife officials have in recent years killed more than 30 wolves accused of livestock attacks. In most of Wyoming, where cattle buoy the economy and wolves are no longer federally protected, the animals can be shot on sight.

That is why conservationists see Colorado — home to the nation’s largest elk herd and vast tracts of public land — as an ideal place to broaden wolf habitat. To overcome decades of resistance from some ranchers, hunters and state wildlife officials, proponents decided to take the idea to the electorate.

The wolf debate is now the latest front in a long-simmering dispute between rural and urban Coloradans over natural resource management, in part because its fate hinges largely on support from voters who are unlikely to encounter wolves. About 75 percent of registered Colorado voters live in metropolitan areas along the Front Range east of the Rockies, far from the people who would eventually live alongside the animals.

“Among ranchers on the western slope, the wolf issue is the number one topic,” said Janie VanWinkle, a fourth-generation rancher who fears for the fate of the 550 cows she runs on her ranch and public lands dotted with snowy peaks and scrubby red-rocked mesas. “There is a face, and there is a family, and there is an economic impact to the decision to reintroduce wolves.”

Some observers see the Colorado measure as pivotal at a time when humans are pushing tens of thousands of species to the brink of extinction. But to successfully restore and preserve biodiversity, voters — especially city-dwellers — cannot simply ink the “yes” bubble on their ballots and walk away, said Marc Bekoff, a professor emeritus in ecology and evolutionary biology at the University of Colorado at Boulder.

“This ballot initiative is raising really important questions about the nature of human-animal interactions over the next century. What happens could serve as a model,” Bekoff said. “These animals are going to need a lot of support on the ground. People are going to have to accept wolves for who they are — they are predators, and they are going to kill animals to eat.”

Opponents have zeroed in on that point, wielding gruesome photos of gutted livestock and pets and images of fang-bearing wolves.

“People on the Front Range need to think about whether they would be voting yes if we were dropping these wolves on the 16th Street Mall in Denver or the Pearl Street Mall in Boulder,” said Ted Harvey, a former state senator and campaign director for the Stop the Wolf political action committee.

Proponents say the risk of wolves attacking people is low, and they note that the measure, Proposition 114, requires state wildlife officials to devise a plan to compensate ranchers for lost livestock.

Even so, 39 of the state’s 64 counties have adopted resolutions opposing the measure — including some in urban areas and the eastern plains. Business groups and agricultural and hunting associations have also come out against the measure.

The outfitting industry worries wolves will kill so many elk and deer that the state will be forced to limit hunting licenses.

“Hunting, fishing and wildlife-watching generate more than $3 billion in economic activity to Colorado every year,” Christian Reece, executive director of Club 20, a nonprofit representing western Colorado businesses and municipalities, said in a statement. Our Western Slope economies can’t afford to take the chance of introducing a species with zero study on the potential economic impacts."

Proponents say elk and deer are still flourishing in northern Rocky Mountain states, where many ranchers are learning to coexist with wolves. There, the animals are credited with helping restore balance to ecosystems by controlling elk and other ungulate populations, preventing them from overgrazing streamside vegetation that is important for beavers, songbirds and fish.

In Colorado, backers toting clipboards outside grocery stores, breweries and bus stops collected more than 200,000 signatures to qualify the measure for the ballot after the state’s wildlife commission — which includes ranchers, hunters and others appointed by the governor — opposed wolf reintroduction three times over the last 38 years.

Mike Phillips, a restoration ecologist and Montana state senator who has been involved in wolf recovery efforts nationwide, said he is optimistic about the animals’ future in Colorado, a state that in recent years has turned from red to purple to blue on the political spectrum.

“Coloradans have more potential to be more accommodating to gray wolves than any state in the country,” he said. “Colorado has much greater diversity in its state legislature and much greater diversity in its electorate to have a very different relationship with gray wolves.”

That relationship has already started. This year, state wildlife officials confirmed that at least six wolves had recolonized northwest Colorado on their own — the state’s first pack since the 1930s.

But scientists said the group is not large or genetically diverse enough to establish a sustainable population. And pro-wolf groups say some of the pioneering wolves may already have been killed just over the border in Wyoming — evidence, they argue, of the need for reintroduction in Colorado. State officials have said they do not know whether the wolves killed were from Colorado.

“It comes down to people, not wolves,” said Stewart Breck, a U.S. Agriculture Department biologist who works with landowners to minimize conflicts with wild carnivores using range riders, guard dogs and other measures.

“If wolves are allowed to be restored here, we have a choice of a hot, flaming inferno of conflict between people yelling hateful statements at each other, litigation, and more livestock and wolves killed,” Breck said during an online forum hosted last month by the Denver Museum of Nature & Science. “Or it can be a slow burn — there will be problems, but we can handle them in better ways that require compromise and people working together.”

Read more: