The Black Hills are thick with lions. But those that leave are unlikely to repopulate the East, study finds

FROM WYOFILE: 

Although cougars have successfully reclaimed much of the West — including parts of Wyoming — new research suggests that expansion to the Great Lakes region and beyond will require reintroductions.

By Mike Koshmrl, WyoFile.com

The robust Black Hills mountain lion population has long been thought of as a conveyor belt of itinerant eastbound animals that will eventually culminate in Puma concolor reoccupying old haunts they were extirpated from long ago.  

The region’s reputation as a lion-dispersal factory is rooted in observation: Animals that have been fitted with tracking collars in the isolated bi-state mountain range have ended up treading into North Dakota, Minnesota, Colorado, Nebraska — and even well beyond. In 2011, a roaming uncollared cat that met its end in an SUV collision near Greenwich, Connecticut, was genetically linked to the Black Hills.

“Black Hills, Black Hills, Black Hills, that’s all people have talked about for years,” said Mark Elbroch, a former Wyoming lion researcher who now directs the puma program for Panthera, a global wild cat conservation organization. “Everyone was like, ‘the Black Hills are the easternmost population’ — which is not true anymore — ‘and it’s the launching point for all of these crazy cats that are going into the Midwest or beyond.’”

New research Elbroch partnered on, however, challenges the presumption that the timberland stretching from Crook and Weston counties into South Dakota is a key cog in the large carnivores’ ongoing recolonization of the United States. 

“What our model shows … is that less than 1% of the cats that are going to be successful establishing territory and finding a mate and raising kittens are going to be from Wyoming,” Elbroch told WyoFile. “That was super surprising. And the reason is that the mortality factors are super high east of Wyoming in the Dakotas.”

The recent peer-reviewed study, Elbroch referred to, “Limited cougar recolonization of eastern North America predicted by an individual-based model,” also casts doubt on the idea that lions will eventually succeed at repopulating significant new habitat beyond their present day range. Although places like Minnesota routinely have tom mountain lions within its borders, successful reoccupation requires that slower-dispersing females make it, too. Then they must find each other and reproduce within adequate habitat.

The study indicates that’s easier said than done — a grim projection, at least for rewilding advocates who’ve eagerly observed the large felines’ successful eastward expansion over the last couple decades.

Unlikely to breed out East

Elbroch partnered on the study, published in the journal Biological Conservation, with Tom Glass, then a University of Montana postdoc researcher working under Hugh Robinson, also at Panthera. The gist of their findings is that lions — largely due to hazards on the landscape that’ll prevent them from getting there — have functionally run out of room. They’ll only reclaim about 2% of unoccupied range by the end of the century. Predictions were for zero mountain lion recolonization in the eastern United States, and only a 30% chance that they’d successfully breed in two states on the fringes of current range, Oklahoma and Minnesota. The most likely area for reoccupation is Canada’s boreal forest: There was a 95% chance of at least one litter born in Manitoba by 2070.

A major factor limiting successful dispersals and establishment of both male and female lions was road ecology. Highways figured into models as gauntlets of death stymying range expansion. 

“Roads play a really big role in limiting them,” said Glass, who’s now a postdoc researcher with the University of Alaska-Fairbanks. “All of these populations that they’ve established so far in the last couple decades — like in the Black Hills and the Badlands — they haven’t had to cross that many high-traffic roads to get there.” 

The study came to its conclusions by using a supercomputer to repeatedly simulate individual animal dispersal attempts. Within the model there was a “submodel” that examined attempts at crossing highways and interstates on the landscape, which increasingly carve up the landscape as cats move east. The road-crossing simulations even factored in mountain lion ages, which influence how they interact with roads: Older adults don’t like to cross larger highways, whereas youngsters are more willing. 

“The interstates just get denser and denser and denser,” Elbroch said. “I think that’s what they run into, shooting off in that direction [to the east]. They’re going to run into roads and people in ag fields protecting their livelihoods.”  

The other big factor limiting recolonization probability was mountain lion hunting on the eastern fringes of present day range, the study concluded.

“This shouldn’t be surprising,” Elbroch said. “Legal hunting impacts the number of cats on the landscape. Importantly for us, it impacts the number of youngsters that are surviving during dispersal.” 

In early October, the South Dakota Game, Fish and Parks Commission will consider a proposal to decrease the mountain lion population in its portion of the Black Hills from 200-300 down to 150-250, according to news reports. The Wyoming Game and Fish Department does not estimate its mountain lion numbers, but hunting seasons allow up to 51 cats to be killed in the three hunt zones encompassing the Black Hills and adjoining Bear Lodge Mountains. Unlimited cats can be killed in the large hunt area that encompasses the outskirts of the region. 

Whole lot of lions

Although Elbroch and Glass’ research suggests that dispersing Black Hills mountain lions aren’t likely to reoccupy the east, it’s not for lack of cats. 

The Black Hills and Bear Lodge Mountain region was actually the one large part of Wyoming where mountain lions were extirpated during the settlement era. But by the 1980s and ‘90s, the stealthy native felines started to gain a foothold in the area, which is typically thick with deer, according to Dan Thompson, Game and Fish’s large carnivore supervisor. 

“There’s a high road density, so you can cover a lot of country,” Thompson said. “I’ve never seen a place where you can see so many lion tracks.” 

In the early 2000s, Thompson actually studied lion dispersal in the region. A couple dozen subadult cats were tracked, and they shot off in many directions. The Black Hills population, he said, “definitely factored” into mountain lion recolonization in North Dakota’s Badlands and in Nebraska. 

Nowadays, those are the easternmost populations in the United States — it’s no longer the Black Hills. In Nebraska, there’s now a breeding population as far as the Niobrara River bluff country more than halfway across the state. 

Elbroch and Glass found that Nebraska’s population, too, has a small likelihood of producing cats that successfully reoccupy eastern North America. More northern populations have the best shot at pulling it off, they found. 

“You see the greatest success from cats that are launching out of eastern Montana and eastern populations in Canada,” Elbroch said. “They have contiguous habitat. It’s big, wide-open country with less people in it. The cats that succeed the most are the ones that go north.”

Game and Fish’s Thompson, like the study’s authors, was surprised by some of the reoccupation model’s conclusions. Humans, he said, can underestimate what’s suitable habitat for mountain lions — arguably, a cornfield could be reasonable habitat for three to four months of the year. 

“I feel like there’s higher potential for cats to move into the Midwest than they found, but that’s just my personal opinion,” Thompson said. “I guess it’s up to lions to tell us if and when they do recolonize.”

WyoFile is an independent nonprofit news organization focused on Wyoming people, places and policy.

This story was posted on September 30, 2024.