Grizzly bears. The biggest, baddest, fiercest, growliest apex predator to prowl the North American continent. Except, well, humans. Since arriving on the scene, people have pushed the Ursus arctos horribilis to the brink of extinction, and then, a few decades ago, threw them a lifeline in the form of the Endangered Species Act. For the iconic grizzly population living in and around the most famous US national park however, that protection could soon be removed.

The Yellowstone grizzlies have recovered remarkably under the Endangered Species Act. But the goal of the law is to get them off the list—once their populations become stable, and the threats to their habitat are mitigated. Which is why the US Fish and Wildlife Service, pointing to evidence of the recovery of the Yellowstone grizzly, recently proposed “delisting” the population and handing the management of the bears to state and tribal agencies, who could permit development, sanction trophy hunts, and allow other activities that would put the bruins in peril (Yellowstone and Grand Teton National Parks, where they would still be protected, only make up a fraction of the bears’ range in the area). Many environmentalists disagree. Some even claim that grizzly bears are more threatened than ever by climate change and human activity, and have questioned the science the FWS used to propose delisting. You might call it one bear of a problem. (Sorry.)

In the early 19th century these most feared of North American predators roamed as far north as Alaska, as far south as Mexico, as far west as the Pacific Ocean, and as far east as Kansas. But the settling of the West nearly wiped out continental grizzly bears except for some swathes of territory bleeding over the Canadian border, and one tear drop of habitat around Yellowstone—representing just 2 percent of its historic habitat—where, in the 1970s, the population teetered at fewer than 150. In 1975, the federal government intervened, granting the Yellowstone grizzlies protection under the Endangered Species Act, which limited hunting and development in the 34,000-square-mile Greater Yellowstone Ecosystem (the national park itself is merely a tenth of the total area). Today, the only place you will find a grizzly bear outside of that area is on the California state flag.

Forty years of endangered species protection has helped the Yellowstone grizzlies rebound to around 700 individuals, and more than double their range (see maps below). A significant accomplishment. “The recovery of the Yellowstone grizzly bear represents a historic success for...wildlife conservation under the Endangered Species Act,” FWS director Dan Ashe said in a statement earlier this spring. Government monitors now say the grizzly population has reached carrying capacity—their habitat can sustain no more. These findings led the FWS to propose delisting the animal.

Yellowstone Science

Getting a species off the Endangered Species list is hard—in 40 years, US Fish and Game has only recovered and removed 35 of the more than 2,000 threatened or endangered species who have been on the list. The task of studying and monitoring grizzlies falls on a government research group called the Interagecy Grizzly Bear Study Team. IGBST (pronounced ‘igbeast,’ we assume) has been hiking through and flying over grizzly habitat for decades, collecting data on the number of separate mother and cub families living in various parts of the ecosystem. Those scientists then run that data through a statistical toolcalled Chao2 and extrapolate the total population size.

IGBST scientists can use annual estimates from years back to calculate population growth or decline. Since the turn of the millennium, they’ve found that population growth has plateaued. Which is how they determined that the Yellowstone grizzlies are now at carrying capacity. “The core of the ecosystem has higher densities of females with cubs in the past decade than ever before,” says Frank van Manen, director of IBGST. “The population has started to fill up all the available habitat and young animals are dispersing out of those areas.”

Van Manen's team also attaches radio collars to grizzlies that beam tracking data to satellites, giving researchers realtime information about where grizzlies move and alerting them when they die. From this data, the IGBST can get a sense of the range and the survival rate of different gender and age bears. Van Manen says their research has shown the survival rate is stable—except for a decline in cub survival, which he believes is due to aggressive male bears, another sign of population density reaching its limit. The hypothesis is backed up by the fact that Yellowstone grizzly bears' range has more than doubled to 22,500 square miles of the total Greater Yellowstone Ecosystem.

So that’s great news, right? The grizzlies, at the brink of extinction a few decade ago, are now bursting out of their habitat.

Not so fast, says wildlife biologist Dave Mattson, leading dissenting voice on the delisting proposal—and a former IGBST member. He looks at the data and sees a different story. “If we’ve reached carrying capacity in the core, it’s actually because carrying capacity has dropped because of the loss of food,” he says. He points to evidence that four of the main grizzly bear food sources—whitebark pine seed, army cutworm moths, elk, and cutthroat trout—are declining thanks to drought, invasive species, and habitat loss. In fact, a prior attempt at delisting the Yellowstone grizzly bear was overturned by a US district court in 2009 in large part due to Mattson’s research on how climate change-decimated whitebark pine (which the FWS has determined is eligible for endangered species status) could affect grizzly bears.

Mattson and others, including a group of 58 scientists led by Jane Goodall—who signed a letter to urging the FWS against delisting—believe the increase in grizzly bear range is actually due to the fact that bears are changing what they’re feeding on and looking farther for food. “They’ve totally fucked it up,” says Mattson about the IGBST conclusions about the grizzly bear population's health. “They missed the mark pretty much entirely.”

Not only that, Mattson says, but the Yellowstone grizzly bears are isolated and still haven't been able to connect with the larger North American grizzly populations in Canada and Alaska. “That intrinsically makes them more vulnerable,” he says. While regulations are in place to protect habitat on federally-owned land—Read: Yellowstone and Grand Teton National Parks and national forests—in the Greater Yellowstone Ecosystem, state and privately-owned land could be logged, mined, or paved with roads. Wildlife managers won't have nearly as much recourse to prevent development there, and citizens will lose their ability to use the ESA to sue to stop it. This, Mattson says, could lead to more fragmentation of an already fragile habitat.

Other scientists agree that it's too soon to say the grizzly bear has recovered. “The population is facing an uncertain future right now,” says Sylvia Fallon, the director of wildlife conservation at the Natural Resources Defense Council. “We think full recovery means addressing the huge amounts of uncertainty around its population size, food sources, and isolation.” Grizzly bears have a very low reproductive rates to begin with, so even a couple dozen trophy-hunted bears (which state wildlife managers in Idaho, Montana, and Wyoming will likely allow) could have serious repercussions for the population's health. Without legal hunting, over 40 grizzly bears diedlast year during or after encounters with humans—which have increased as bears range farther into areas where hikers hike, livestock range, and hunters stalk deer, elk, and other ungulates.

But van Manen counters that recent research shows even with declining sustenance like whitebark pine seeds, grizzly bears have proven very adaptable omnivores and have been able to switch to other food sources like bison carcass, ants, dandelions, and clover. "We have not seen changes in body mass of bears," he says. Furthermore, a genetic study of Yellowstone grizzly bears published last fall by the IGBST showed stable genetic diversity, and no reason to believe it would decline as long as the population stayed above 600. Even if that did happen, van Manen says, they could transport a bear from a northern population and have it mate with Yellowstone bears, a method proven successful with the Florida panther. In any case, the post-delisting conservation plan mandates continued monitoring of the population to makes sure it doesn't dip below 600 bears.

That evidence, plus the rest of the IGBST's findings have the FWS leaning towards delisting. "It is not the purpose of the ESA to list species in perpetuity," FWS spokeswoman Serena Baker said in an email. "Once the science indicates a species or population has recovered, it is the duty of the Service to delist it." Furthermore, if they don't the very integrity of the ESA—already under constant threat from conservative lawmakers—could be undermined. "The ESA needs success stories to strengthen the law, and the Yellowstone grizzly bear is the greatest success story of all," the recently-retired FWS grizzly bear recovery coordinator Chris Servheen told High Country News. The FWS has completed two public hearings this spring and received over 100,000 written comments.

The agency will sift through feedback and go through more peer review before making a final delisting decision by the end of the year. But even if they do not delist, the ESA hasn't necessarily failed. Out of all the species listed as threatened or endangered under the Act, only ten have gone extinct. Despite what Hugh Glass might have to say, that the Yellowstone grizzly hasn't joined that group is something to roar about.