JACKSON — In the late 2000s, Kira Cassidy watched the Slough Creek wolf pack in Yellowstone National Park shrink from roughly 17 wolves down to about three — in only a year and a half.
“Their alpha male had been hit by a car. I think one of the other wolves was shot outside the park,” Cassidy said. “They just spiraled downward and eventually dissolved and another pack took their territory.”
Cassidy, a research associate with the Yellowstone Wolf Project, said that pack’s demise indicates what happens when humans kill wolves — intentionally or not — that dwell in national parks and preserves. Packs become less likely to reproduce and stick together than packs whose members aren’t killed by hunting, predator control, poaching, vehicle strikes or research captures gone wrong.
That’s a new finding, one that Cassidy and 12 other researchers from reserves and universities in the heart of gray wolf country published Tuesday in the scientific journal “Frontiers in Ecology and the Environment.”
Cassidy was the lead author on the study.
Covering 30 or so years of data from parks and preserves in Wyoming, Alaska and Minnesota, the paper shows that the vast majority of park wolves killed by humans are killed outside protected areas.
It also calls for policies and working with adjacent wildlife managers to address pack disruptions.
Inside a park or preserve, managers focus on maintaining natural systems. Hunting is usually not allowed.
But state wildlife agencies that manage animals on the other side of the border typically have different priorities, or at least answer to different constituents than their federal partners. Predator control may be prioritized. There may be strong anti-wolf sentiment. Hunting may be encouraged.
Cassidy said that only 7% of the wolves killed during the study were killed inside Yellowstone, Grand Teton National Park or the three other areas included in the study: Voyageurs National Park in Minnesota and Denali National Park and Preserve and Yukon-Charley Rivers National Preserve in Alaska.
In Yellowstone, the wolves collared in the park spent only 4% of their time outside of its boundaries. But Grand Teton’s research wolves spent about 50% of their time abroad, similar to their counterparts in Voyageurs.
“The amount of time those wolves spend outside of the park is really quite staggering,” said Thomas Gable, one of Cassidy’s co-authors and the project lead of the Voyageurs Wolf Project. That’s a University of Minnesota research project that studies wolf ecology around the midwestern park.
Packs are essential to wolf life. They enable wolves to hunt cooperatively and defend territory. Wolves also rely on one another to breed in late winter, have pups in early spring, and raise those pups throughout the year. Gable said asking why packs are important to wolves’ survival is a fundamental question.
“It’d be kind of like saying why are families so important to human societies?” Gable said.
The 25-plus years of data Cassidy, Gable and 11 other researchers analyzed showed that when humans killed a member of a wolf pack, the pack became 27% less likely to stick together the next year.
The wolves also became 22% less likely to reproduce.
That’s compared to wolf packs that didn’t experience human-caused mortality. The paper did not investigate what happens when wolves die naturally, though that will likely be the subject of a later study, Cassidy said.
But when humans killed a pack leader, responsible for breeding and holding its brethren together, the effects were more severe. Packs were 71% less likely to stick together and 49% less likely to reproduce.
“It is more detrimental to lose a leader than any other wolf,” Cassidy said.
Big packs, however, stand up better than smaller packs to human-caused mortality.
In 2021 the Phantom Lake Pack had roughly 13 members when state wildlife officials authorized an aggressive wolf hunt in southern Montana. Park officials think the pack’s breeding female was one of the first to go. About six members were killed. The pack dissolved, leaving only the alpha male.
“He was the only one we caught on camera for six months, just by himself,” Cassidy said.
But other packs, like Junction Butte Pack, weathered the hunt fairly well. When hunters started firing, that pack was 28 wolves strong, Cassidy said. It lost eight members, but none of them were pack leaders.
“Bigger packs were better able to withstand the instability caused by human-caused loss,” Cassidy said.
But even with events like the 2021 hunt in Montana, which wiped out about 19% of Yellowstone’s wolves, the controversial canines researchers studied aren’t necessarily struggling. When one pack dissolves, another pack usually takes its place. Population numbers have also been relatively stable. In Yellowstone, for example, wolf populations have hovered around 100 animals for 13 years, Cassidy said.
That’s part of why Cassidy and the other researchers conducted the study. Human-caused mortality has largely been studied in the context of population-wide shifts — and it typically has little effect.
“Wolves can take a lot of human killing. That is true,” said Doug Smith, Yellowstone’s now retired wolf biologist of 28 years. He was one of Cassidy’s 12 co-authors. “But it’s at the population level.”
How killing wolves affects pack dynamics hasn’t been explored much, Smith and Cassidy said.
Because living in packs is such a crucial part of wolf ecology, the scientists said it’s critical for federal wildlife managers to understand how hunting and human-caused deaths affects wolf social structure. Parks are charged with maintaining “natural systems,” Smith said. Wolf packs are a critical part of that.
Before the paper was released, Smith described putting some of its insights to work, lobbying the Montana Fish and Wildlife Commission to reduce quotas in hunt areas just north of the park.
This hunting season, Smith and Yellowstone Superintendent Cam Sholly convinced commissioners to drop the quota from 10 to six wolves in wolf management unit 313, aiming to minimize mortality — and, as a result, keep packs together. During the previous season, that sliver of territory had been included in a larger hunt area. Once 82 wolves were killed there, commissioners closed the hunt. This year, unit 313 was pulled out of that larger block, which is farther north and retains an 82-wolf quota.
Smith and Sholly got part of what they wanted: a lower quota on Yellowstone's immediate northern border.
But they weren’t able to convince Montana officials to keep the hunt area directly north of Yellowstone divided in two. Doing so, Smith said, would have split the six-wolf limit over two geographic areas, minimizing the risk of killing six wolves from one pack.
For a wolf pack with 10 members, killing six wolves would all but certainly wipe it out, Smith said: “They’re going to go under.”.
Still, the retired wolf biologist said the quota reduction was a win — similar to what he hopes the paper will accomplish. Smith wants federal officials and their neighboring wildlife managers to talk more.
“The sweet spot is compromise,” Smith said. “We’re constantly trying to lower take and they’re trying to bring it up. And so we’ve got to cross somewhere in the middle. That’s the sweet spot.”
Park scientists said they have work to do internally.
To protect pack dynamics in parks like Grand Teton, where 35% of wolves studied were killed by vehicles, Cassidy and her 12 co-authors say lower speed limits and wildlife crossings could help. In Yellowstone, Cassidy said, park officials could also do a better job keeping wolves from becoming habituated.
That, she said, “makes them more vulnerable to all kinds of losses.”
In Yellowstone, where studied wolves spend only 4% of their time outside the park, 22% are killed while roaming elsewhere. In similar situations, researchers call for ensuring “that the proportion of human-caused mortalities more closely matches the proportion of time wolves spend outside park boundaries.”
They suggest jurisdictions adjacent to parks — for instance, areas administered by the Montana Department of Fish, Wildlife and Parks and Wyoming Game and Fish Department — “adjust hunting seasons and lethal control near parks to accommodate cross-boundary movements and stability of packs.”
What that would look like is hard to say.
“I don’t think the purpose of the paper was to be prescriptive,” Smith said.
Rather, Smith said, it calls for better cooperation between National Park Service units and the agencies that manage wildlife on their doorstep. But he stopped short of calling for specific policy change.
“Communication is key,” Smith said. “Agencies need to talk.”