The fight to save America’s most endangered mammal

Dedicated captive breeding and reintroduction efforts have brought black-footed ferrets, America’s most endangered mammal, back from the brink. A recent successful cloning of a ferret named Elizabeth Ann even offers the hope of restoring genetic diversity to these mammals.

But despite it all, these animals—agile, elongated mustelids with black masks—may still die out. Because in order to save a species, you can’t just save individuals—you have to save its habitat.

Without sufficient protected habitat, the black-footed ferret is destined to spend the rest of its existence in zoos and captive breeding centers unless it can return to its native grasslands, which have been widely plowed, paved, or subjected to poison to control creatures deemed pests. That’s why many scientists and conservation advocates believe the battle for the future of Wyoming’s Thunder Basin National Grassland is the battle for this emblematic species itself.

“They’re beautiful, elegant–but beyond that, they represent an ecosystem [grasslands] that is dying in North America,” says Michael Lockhart, the former black-footed ferret recovery recovery coordinator for the U.S. Fish and Wildlife Service (FWS).

The Thunder Basin grassland covers more than half a million acres of land in northeastern Wyoming, representing a large portion of the just under four million acres of national grasslands in the United States (in comparison, the Forest Service oversees more than 188 million acres of national forest in the country). At high elevation and cold, the prairie is not welcoming to most crops, but more than 800 native plants take root there as well as a diverse web of grassland animals including black-tailed prairie dogs, mountain plover, burrowing owls, ferruginous hawks, and swift foxes.

Ferret habitat historically covered about 100 million acres of grasslands from Canada to Mexico and the nocturnal creatures lived in prairie dog towns, making their homes in the rodents’ burrows. Ferrets particularly favored black-tailed prairie dog colonies, like the ones that currently cover Thunder Basin. The site is among all the major ones Lockhart had identified as promising for ferret recovery during his tenure as the official recovery coordinator. It’s a rare gem for reintroduction—a large, protected expanse of grassy habitat with abundant prairie dogs, ferrets’ favorite food.

We only need to protect 500,000 acres of prairie dog lands in order to recover ferrets, says Kristy Bly, a senior conservation biologist with the World Wildlife Fund. “We’re dealing with two percent of the former abundance and distribution of prairie dogs in North America,” she says. “It should be a no-brainer.” But the conflict between officials, conservationists, and ranchers at Thunder Basin has been anything but simple. Here, more than a million acres of private and state lands intermingle with the public lands, and this close relationship has brought out sharp contrasts in beliefs about how the grassland—and public lands in general—should be managed.

This conflict has a long history.

Starting in the late 1800s, settlers of the Great Basin poisoned prairie dogs to leave more grass for their cattle. Grasslands, with their deep, rich soil, were also widely converted to farms. A disease brought to States in the early 1900s—sylvatic plague—has also decimated prairie dog populations, since the rodents have no immunity to the introduced pathogen. Ferrets prey exclusively on prairie dogs, so the demise of the burrowing rodent took down the slender mustelids too.

This was especially devastating because ferrets, despite their diminutive size, are territorial and require large expanses of prairie dog colonies. Wildlife officials estimate that more than 15,000 acres of prairie dog colonies are needed to provide for a self-sustaining ferret population with 100 breeding adults. Although prairie dogs continued to scrape by despite extermination efforts, black-footed ferrets tanked. The federal government deemed them endangered in 1967 (in legislation that predated the Endangered Species Act of 1973), and presumed the ferrets to be extinct in 1979.

Then, in 1981 on a ranch near Meeteetse, Wyoming, a dog named Shep brought home a dead ferret. Wildlife officials rushed to capture the surviving mustelids nearby. All ferrets living today are descendents of 15 individuals from this last haven of black-footed ferrets.

Later in 1981, a Forest Service ranger reported a ferret sighting at Thunder Basin after one scampered across the road in front of the ranger’s truck. Illuminated in the beam of the headlights, the ferret and the ranger stared at each other for one and a half minutes, before it padded away into the night. After that, officials never again spotted any ferrets in the area.

Around 2008, after decades of captive breeding and reintroduction efforts, the weasel-like animals seemed to have a fighting chance of gaining a foothold back in their native grasslands. There were over 1,000 alive in the wild, and wild-borne ferrets had the potential to seed new populations (ideal because captive-borne individuals have a harder time surviving on the prairie). “We were going to be able to meet the downlisting goal just in a few more years,” says Lockhart, the former FWS official.

[Related: Why these towns are trying to save an ‘agricultural pest’]

But rapid prairie dog proliferation in the past decade has raised controversy. Between 2015 and 2017, the rodents rippled across more than 75,000 acres of the prairie. “You could step out of your vehicle and it looked like the ground was rolling, there were so many prairie dogs” says Dave Pellatz, executive director of the Thunder Basin Prairie Ecosystem Association, a nonprofit whose members include ranchers and conservationists based in northeastern Wyoming.

It was a time of drought, which increased tensions on the rangeland. Prairie dog colonies expand in dry years. Ranchers claim that their livestock went hungry as the prairie dogs grazed across a larger area. “We had a situation where the combination of all the grazers [livestock and prairie dogs] were eating far more than the land could produce,” says Pellatz. “That’s certainly an immediate economic impact [for ranchers].”

Under a previous agreement, the Forest Service’s objective was to protect 33,000 acres for prairie dogs. But, under pressure to do something about the ballooning numbers, officials proposed a new plan that capped prairie dog habitat to 10,000 acres, and to 7,500 in drought years. This plan, which went into effect in December, also allows people to shoot prairie dogs recreationally and expands the use of poison to prevent the rodents from encroaching onto ranching properties.

Wildlife experts involved in the planning meetings for the change say that the amendment is largely the result of pressure from a handful of nearby landowners, who received support from state lawmakers including the governor. Ana Davidson, an ecologist at Colorado State University in Fort Collins who attended the meetings, says that she observed a “heavy bias” against prairie dog conservation, and reports that she was cut off from speaking at times. “There are also really strong statements by some of the ranchers that just spoke towards a different, strong attitude about how they see the use of the public lands, and that they need to be surrounding livestock production,” she says.

Forest Service lands are “multi-use,” meaning the agency is supposed to balance the needs of plants, wildlife, and people in places like the Thunder Basin. While that provision often does permit livestock grazing, it also means that the agency has some responsibility to protect wild residents too. Lobbying from individuals representing less than 10 ranches apparently swayed the Forest Service. To Davidson, it begs the question: “what is public land for?”

In a letter in response to the draft environmental impact statement for the decision, Lockhart made his opinion on the matter clear. The plan change would “largely foreclose” the potential to recover the ferrets on a “critically important parcel of Public Land,” he wrote (emphasis his). “Given the enormous resources and work put into ferret recovery over the past three decades by State and Federal wildlife agencies, zoos, conservation organizations and international partners it is unforgivable to take off the table potentially one of the best future ferret reintroduction sites in N. America.”

Officials from the Fish and Wildlife Service, the main agency enforcing the Endangered Species Act, also appear to believe Thunder Basin to be of immense value for ferret recovery. “The [Thunder Basin National Grassland] is one of the few large grassland properties in federal ownership with extensive black-tailed prairie dog populations,” Noreen Walsh, the regional director for the mountain-prairie FWS region, wrote to the regional forester for the Forest Service in 2017 (the letter was obtained in a public records request by staff at the nonprofit Defenders of Wildlife). “While there are no immediate plans to reintroduce the ferret at TBNG, it may well be the best existing site across the species’ range in 12 western states, Mexico, and Canada.”

In the 2013 FWS plan for ferret recovery, the authors wrote: “We believe the single, most feasible action that would benefit black-footed ferret recovery is to improve prairie dog conservation.” Prairie dogs have the strange position of being the keystone to rebuilding ferret populations—and really, North American grasslands in general—while also being officially described as an “agricultural pest.” (Popular Science contacted the FWS multiple times, but the agency was not able to arrange an interview prior to the publication of this story).

Now, experts say that it’s unlikely the Thunder Basin prairie can house a self-sustaining population—especially with the continued threat of plague. In order for the mammals to escape their endangered status, one major criteria is that they need 10 populations of at least 100 breeding adults. Right now, there are zero sites that meet this requirement (a couple reintroduction sites have met this goal in the past, but the numbers went down after plague outbreaks), and only about 340 ferrets total are scattered about in the wild currently. In the previous iteration of the Thunder Basin plan, officials had protected enough prairie dog acreage to support a population of 100 ferrets and a portion of the range was officially called “Black-Footed Ferret Reintroduction Habitat.”

Pellatz says there are other grasslands in which to reintroduce ferrets—that Thunder Basin isn’t the end-all for the masked mammals. But biologists familiar with the matter contend that Thunder Basin is a critical site. “Conata Basin [in South Dakota] and Thunder Basin are it,” says Lockhart. “In terms of their history and potential, they are head and tails above anything else.”

Some ecologists believe there could be a sustainable balance between setting the stage for ferrets and maintaining cattle. Studies of bison have, for example, shown that the buffalo prefer to graze on prairie dog colonies, and even gain more weight when they do so. That’s because prairie dog grazing can encourage the growth of diverse grasses rich in nutrients. After all, bison—which once numbered in the tens of millions in North America—seemed to find enough to eat for the thousands of years they lived alongside prairie dogs and ferrets in the plains.

Though some research has found cattle also prefer to graze alongside prairie dogs, the rodent-ungulate relationship is fickle in ways that aren’t fully understood. One major variable is rain, says Kristy Bly, senior conservation biologist with the World Wildlife Fund. When rainfall is plentiful, there’s more likely to be enough forage for all grass-eaters. But when the range gets dry, as Thunder Basin did in the 2010s, that once-beneficial (or at least neutral) relationship can turn sour.

Bly says that continued research into this relationship can help inform solutions. Some of that research is already in the works.

[Related: The endangered species list is full of ghosts]

Davidson is part of a team funded by the USDA that’s trying to illuminate the impacts of prairie dog densities and colony size on cattle weight gains at Thunder Basin. To do so, the scientists are teaming up with local ranchers. Half of the ranchers are helping with the project design and gathering data, including by weighing their cows, while the rest are not directly involved. Beyond quantifying how many prairie dogs it takes before cows start to lose weight, Davidson says the big picture objective is seeing how the collaborative effort affects trust. “Right now, we’re in a landscape where science is not well-trusted,” she says. “Is this a way to get people to start to trust science and scientists?”

Demonstrating how conservation and grazing can coexist is key, says Pellatz. To increase acceptance of prairie dogs and thus the chances of returning ferrets to the land, he says, “we have to convince landowners they won’t have their livelihoods destroyed.”

But there may never be agreement if this is a matter of a fundamental difference in how the parties see the function of public lands, which, in theory, are as much the domain of the Wyoming ranchers as they are an apartment dweller in NYC. Protecting endangered species is very popular with the American public—four out of five Americans support the Endangered Species Act. While this majority would likely favor restoring ferrets, a relative few were able to influence decisions on the ground at Thunder Basin.

According to some advocates, continued compromises with the little land left that could house ferrets are part of the problem. They allege that the compromises have yielded more and more to ranchers, at the expense of the prairie ecosystem. “The collaborations yielded this environmental disaster,” says Erik Molvar, the executive director of the conservation group Western Watersheds Project. “There’s no trust left here. We just need to enforce the federal law and be done with it.” To that end, his organization is planning to sue the Forest Service, accusing them of having violated their legal obligation to do its part to restore endangered species. (The Forest Service declined an interview request with Popular Science, stating their staff are not allowed to comment on decisions being litigated).

“Being able to tolerate wildlife should be part of doing business,” says Lauren McCain, a senior federal lands policy analyst with the advocacy group Defenders of Wildlife. “If there are more cows than can be supported on the [public] land, whether it’s inhabited by prairie dogs or not, there should be adjustments in cattle stocking.”

On other public and tribal lands, ferrets have had better luck. In Conata Basin, South Dakota, ferrets were reintroduced in 1996 and have since become the most successful wild population. Like Thunder Basin, the area also neighbors private lands. Bly of the World Wildlife Fund says the reason the reintroduction has been successful is because Forest Service officials there have worked hard to control prairie dogs on the borders of the national grassland, which eased the grumbling of landowners over the rodents.

Balancing dichotomous opinions on prairie dogs and public land is a taxing job for federal officials, one that requires dedication. “When Conata Basin took off and was doing really really well, it was because there was a Forest Service ranger who was absolutely devoted to [ferret recovery],” says Lockhart. In the case of Thunder Basin, he believes the Forest Service caved to political pressure.

Another problem is that continued management of ferret lands is expensive and has no dedicated line item in the federal budget, says Bly. Controlling plague alone costs $40,000 annually for a 1,500-acre ferret reintroduction area. While she’s happy about the successes of captive breeding and cloning, Bly says that there hasn’t been a commensurate amount of money made available for reintroduction and management of wild ferrets.

Whether the solution is officials taking a stronger stand for the endangered ferrets, a collaborative effort between ecologists and ranchers, or some combination thereof, the fact that a handful of individuals were able to sway management on a federal grassland perhaps reveals the vulnerability of the prairie. A 2004 report published by the US Geological Survey on the state of the Great Plains used surprisingly firm language on the matter: “We offer that North America’s Great Plains have suffered from an abundance of fiscal greed and a shortfall of ecological common sense.” The plight of the black-footed ferret might be a warning.