Griz connectivity map

Male grizzly bears have a relatively high probability of dispersing through areas in purple and pink, potential linkage zones that connect the Greater Yellowstone and Northern Continental Divide ecosystems. 

When a grizzly bear wanders along the northern fringes of the Yellowstone region, what’s the likelihood it could happen upon the complex of wildlands surrounding Glacier National Park?

New research from the Interagency Grizzly Bear Study Team says that — at least in a year — it’s impossible.

Such a trek requires either taking a straight shot and traversing large agricultural valleys in Montana, or swinging wide to the west on a 200-mile-long arc through relative wildland.

“In one season no bear actually made it from one ecosystem to the other,” said Frank van Manen, who leads the study team. “And that’s doing 20,000 simulations. They were given plenty of chances.”

Given several years, however, such a journey was “probably” doable, he said.

Slim odds of transecosystem travel aside, van Manen found the new research on the potential connectivity of the two grizzly populations promising.

“There were more routes than we anticipated,” he said. “And there are a variety of choices.”

The routes are described in the latest edition of the Ecological Society of America’s academic journal, Ecosphere, in a paper titled “Potential paths for male-mediated gene flow from an isolated grizzly bear population.” Staff from Wyoming and Montana’s state wildlife agencies were listed as co-authors.

To identify the routes the biologists took real-world GPS location data from 124 male bears in the two ecosystems that has accumulated since 2000. Their precise locations showed how males move around the landscape. Then, using population data and factoring in human influences, like road densities, they simulated the paths grizzlies could take to get from one gene pool to the next.

The easternmost high-probability route, which is the most direct, passes through the Big Belt and Bridger ranges above Bozeman on the way to the Absaroka Range.

The largest number of passageways, however, swung to the west, converging in the Tobacco Root Mountains south of Butte, Montana, before pouring into the Greater Yellowstone Ecosystem in the Madison and Gravelly ranges. One of these paths originated in the Rattlesnake-Garnet ranges, then traversed the John Long, Flint Creek, Anaconda, Pioneer and Highland ranges. The other began in the Nevada-Garnet ranges and crossed the Boulder Mountains before it dumped into the Tobacco Roots.

One major impediment

There has never been a documented case of a grizzly hopping ecosystems from the Greater Yellowstone to the Northern Continental Divide, one way or the other.

The topic of connectivity between the two populations is hot, especially in the wake of a U.S. Fish and Wildlife Service decision that removed protections for the Yellowstone region’s bears and opened them up to being hunted. Bears on the fringes of the region are now wholly managed by the states, with no federal oversight.

Courts are also sorting out the legality of delisting a distinct island population of animal that was formerly protected by the Endangered Species Act — like Yellowstone grizzlies.

All parties involved, including conservation groups and the agencies, have sought to ensure that genes naturally flow from one population to the next. A major impediment is the distance between: There’s a nearly 60-mile gap between where grizzlies are known to live today, and the connecting routes identified by van Manen’s study ranged from 85 to 220 miles.

On-the-ground conservation

David Mattson, a former federal grizzly bear researcher, discounted the study, calling it “inane” and politically driven.

“It’s substantively misleading,” he said, “because they don’t address the most important aspects of colonizing landscapes: survival and reproduction.”

The route a grizzly bear takes to “sprint from one ecosystem to the other,” he said, is inconsequential to the bigger picture of connecting the two populations permanently.

Van Manen was hopeful that the study could lead to on-the-ground conservation. The new knowledge about range expansion and linkages, he said, could be used by managers and advocates arranging easements on private lands that fall within likely grizzly crossover territory. It could help in the siting of crossing structures on highways, or determine where to direct information and education campaigns about grizzly coexistence before the bears arrive.

“I&E programs could go a long way for preparing people for these movements,” van Manen said. “I think preparing people for that is half the battle in avoiding human-bear conflict.”

Contact Mike Koshmrl at 732-7067, env@jhnewsandguide.com or @JHNGenviro.

Mike has reported on the Greater Yellowstone Ecosystem's wildlife, wildlands and the agencies that manage them for 7 years. A native Minnesotan, he arrived in the West to study environmental journalism at the University of Colorado.

(2) comments

Leslie Patten

One big question about an eastern route: I90?

Chad guenter

Advocates for these "easements" through private land holding can start raising money to pay WILLING landowners their desired price if they accepted an offer. No tax money or forcing landowners to sell should even be considered for this idea.

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