Potential paths of the grizzly bear identified

Male grizzly bears from the Northern Continental Divide population near Montana’s Glacier National Park could reach the Greater Yellowstone Ecosystem in a few years, researchers say.

A study published Oct. 23 in the journal “Ecosphere” shows possible paths that wandering bears from the Glacier or Yellowstone areas could take to the other ecosystem.

In 2016 and 2017 several bears from the Northern Continental Divide population were seen pushing beyond their normal range, covering about half the distance between the two ecosystems, said Frank van Manen, an author of the paper and team leader of the Interagency Grizzly Bear Study Team.

“Something seems to be happening with those populations,” he said.

Male bears typically disperse further than females, and so far it seems to be predominantly Northern Continental Divide bears heading south, not  Yellowstone bears heading to the Northern Continental Divide. Biologists don’t know why.

It’s also unknown if the populations ever used to mingle — there aren’t records going back far enough to say, van Manen said. The Yellowstone bears have likely been an isolated population for at least 100 years, he said. The Northern Continental Divide bears are able to mix and mate with grizzlies in Canada.

The study examines potential bear travel corridors, not locations where they would stop to live, van Manen said.

Researchers used GPS data from 124 male bears in the two ecosystems to see how the animals moved across the landscape and identify potential routes. They then factored in human influences, like roads and development, to simulate ways the bears might move from one ecosystem to the other.

“For the first time we are getting a sense of how those bears would need to navigate,” van Manen said.

Some theoretical paths are shorter, but more likely to take bears near development. Other options provide greater habitat security but extend the journey by as much as 200 miles.

While van Manen thinks a bear might complete the trek sometime in the next five to 10 years, he doesn’t anticipate an animal making the entire crossing in a single year. Instead, a wandering male might push out from its home range and continue farther the following year. It might be an exploratory bear that inches closer to Yellowstone for several years before making it, he said.

Wildlife scientists, land managers and conservationists have discussed connecting the two bear populations for years, but the interest in the topic has spiked since the Yellowstone bears were removed from the endangered species list this summer.

Linking the two groups is crucial for long-term viability of the Yellowstone population, conservation groups such as Earthjustice say.

“Hats off to them for looking at it, but it underscores the decision to delist the bears was premature,” said Timothy Preso, a managing attorney with Earthjustice’s Northern Rockies office. Earthjustice has sued over the decision to remove federal protections for Yellowstone grizzlies.

To move between the two ecosystems, bears must leave the established monitoring areas. Once outside those boundaries bear deaths no longer count toward the mortality thresholds used to ensure the population doesn’t plummet.

“Bears outside that demographic monitoring area are basically bears that don’t count,” Preso said. “There are no frameworks in place to facilitate bear movement through those connectivity zones.”

Pioneering bears moving to new country face an arduous journey, and will likely travel through valleys with greater potential for human and livestock conflicts — and the associated repercussions — but no federal oversight, Preso said.

Bears are unaware that the rules change when they cross an invisible line.

“And in many ways, those are the bears we really need,” he said.

Preso said “the holy grail” for grizzly bear recovery in the Northern Rockies would be a connected population from Yellowstone to Canada with bears reoccupying the Selway-Bitterroot Wilderness area in Montana. That would ensure genetic diversity and a robust population that could weather losses from natural causes, environmental changes and human conflicts.

Van Manen disagrees about the importance of connecting the populations. The Yellowstone bears are isolated and less genetically diverse than other bear populations, “But despite all that, there is no immediate concern regarding genetic diversity,” he said.

A paper published in 2015 shows that Yellowstone bears have maintained genetic diversity through population growth.

Plus, from a genetic standpoint, the Yellowstone bears would only need to mingle with one or two bears from an outside populations to increase genetic diversity, van Manen said.

The most recent study outlining potential connecting pathways was done at the request of wildlife managers, he said. Ideally it will help agencies, such as departments of transportation, plan for ways to help bears move across the landscape.

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The 21 confirmed bear observations documented in the area separating the groups are an important reminder to people who live between Glacier and Yellowstone National Parks.

“People should not be surprised to see a grizzly bear in any of those areas between them,” van Manen said. “They could show up just about anywhere.”

Even after a bear successfully makes the journey, van Manen believes it will continue to be a rare event. Crossing between ecosystems will remain a daunting endeavor.

Earthjustice plans to continue its legal challenge to the removal of the bears from the endangered species list, Preso said. But assuming the bears remain delisted, he hopes the state of Montana will impose protections for the animals in the connectivity zones, including more tempered responses to livestock predation. Preso also said he hopes managers will work with people in the potential pathways to educate them on food and garbage storage and other bear safety measures to help prevent human-bear conflicts.