The Greater Yellowstone Ecosystem’s grizzly population continues to stagnate geographically, a relatively new trend that wildlife managers say is related to bears saturating “suitable habitat” where the species is tolerated.  That finding is described in a new and first-ever rangewide rep ort summarizing where grizzly bears are found in the Lower 48. Overall, grizzlies, which are classified as “threatened” under the Endangered Species Act, continued their decades-long recovery and reoccupied 4% more habitat over the past two years. That equates to a rangewide expansion of roughly 2,250 square miles, or an area about two-thirds the size of Yellowstone National Park.   Grizzly bears occupy an estimated 59,000 square miles of habitat throughout all their recovery zones in the Lower 48. (Cecily Costello) But bruins that dwell in the tri-state Yellowstone area were the exception. The estimated 1,050 grizzlies there occupied about 3.5% less ground, or about 963 fewer square miles, than they did two years ago. The report does not address what drove the change, but lead author and Montana Fish, Wildlife and Parks research biologist Cecily Costello said it’s likely related to grizzlies running out of ideal habitat in the modern West. “When you look at the habitat to the east of the Yellowstone Ecosystem, to the south of Yellowstone, you’re looking at a lot of open prairie,” Costello said. “There’s not really big river valleys those bears could move into. There’s a little bit of a limitation in terms of the range expansion in those directions.”  Wyoming grizzly managers see it similarly, attributing the slight retreat to bears losing spaces where they can live without getting into trouble.  “I think it’s just indicative of where the population is,” said Dan Thompson, large carnivore supervisor for the Wyoming Game and Fish Department. “I don’t think we should expect it to expand.”  The occupied grizzly bear range in the Yellowstone region is retreating slightly and encompasses an estimated 26,100 square miles, nearly two thirds of which is located in Wyoming. (Cecily Costello) Matt Gould, the Interagency Grizzly Bear Study Team’s new leader, agreed. His predecessor, Frank van Manen, predicted about a decade ago that the grizzly population in the Yellowstone region would soon stabilize — and now it seems to be doing just that.  “Occupied range has kind of waned up, and now it’s kind of slightly decreasing,” Gould said. “It’ll be interesting to see: ‘Does it drastically drop, or is it going to stay steady and bounce around?’”  Stopped expanding Biologists first documented the end of a half-century-long era of grizzly range expansion in the Yellowstone area two years ago. At the time, federal scientists observed a 0.5% reduction in the species’ overall distribution — a retreat of 142 square miles.  The mapping Costello and her co-authors just completed examined the period from 2010 to 2024. Distribution in the Yellowstone and Northern Continental Divide ecosystem is based on hard data — from tracked bears, conflicts and other verified observations — over a 15-year rolling window.  The data is smoothed out based on the whereabouts of all grizzlies known to exist in any given area. For that reason, bears that make “outlier” movements, like the subadult male that reachedthe Bighorns in 2024, don’t usually influence the distribution maps. Contraction in the Yellowstone Ecosystem’s occupied range comes at a time when there has been a record number of bears dying, though grizzly biologists say they don’t necessarily see the two trends as being related.  A hunter-killed grizzly bear shot in the Absaroka Range’s Aspen Creek drainage in 2014. (U.S. Fish and Wildlife Service) Mortality hit a high in 2024, with 72 known grizzlies that died that calendar year, Gould said. The death toll this year is almost the same, at 71, which is about 35% greater than the 10-year average of 54 mortalities.  The leading causes of death, according to Gould, were livestock conflict (21 grizzlies killed as a result), followed by “site conflicts with humans” (16 grizzlies), self-defense killings (12 grizzlies), accidental deaths (nine grizzlies) and natural causes like predation (six grizzlies).  This year, three in four Yellowstone-area grizzly deaths were within a zone in the core of the ecosystem known as the “demographic monitoring area.” That’s a slightly higher rate than average.  Where habitat’s retreating Wildlife managers count bears in the demographic monitoring area. This area was declared fully occupied by bears in 2019.  In Costello’s distribution report, this “core” area represented 71% of where grizzlies were found in 2024. The other 29% of the occupied range fell outside of this core area on the fringes of the mountainous, public land-dominated ecosystem. This is where grizzly range has been retreating. When Yellowstone ecosystem grizzly distribution reached its peak in 2021, more than 40% of occupied range was mapped outside the core zone. Last year, the largest contraction in occupied Yellowstone habitat was located in eastern Idaho in the Big Hole Mountains and Snake River Range. Another recession appears in Montana’s Ruby Range, maps from the report show, and there’s a small loss of occupied range in the South Pass area off the tip of the Wyoming River Range.  Costello, who compiled the maps, said she doesn’t put a “whole lot of stock” into small regional changes. “The edges are a little bit uncertain,” she said, “because you have less [grizzly data] about the edges than you do about the middle.” The other major population of grizzly bears in the Lower 48 dwell in Montana’s Northern Continental Divide Ecosystem. Occupied grizzly range stretched by 2,500 square miles, a nearly 12% increase. These bears mostly pressed into new habitat on the eastern and southern sides of the ecosystem, gaining ground in the Sapphire Range, and Boulder and Big Belt Mountains, maps show. There are more than 24,000 square miles of occupied grizzly bear range in the Northern Continental Divide Ecosystem, a 12% increase from an assessment two years ago. (Cecily Costello) The Northern Continental Divide Ecosystem’s occupied range encompasses much more open prairie than to the south in the Greater Yellowstone Ecosystem. Partly, that’s explained by Montana grizzlies moving down big river corridors, Costello said. When a bunch of them make the movement, the occupied range line can “pull out really quickly.” Smoothing of the data can then make it look like they’ve reoccupied big chunks of open country, she said. Habitat is another explanation for why western Montana occupied grizzly range keeps stretching while Yellowstone-area bears have held steady and retreated in places.    “When you look at the plant communities and mountains that exist in western Montana, there’s still a lot of what could be considered decent bear habitat,” Costello said. “It’s the expectation that we’ll probably continue to see bears moving into those habitats.”  A lot of that growth is expected to take grizzly populations toward Idaho’s Bitterroot Ecosystem, which has been unoccupied since the species was wiped out there in the 1950s.  The post Yellowstone grizzly range contracts by 4%, while ‘Northern Continental Divide’ bears gain 12% more ground appeared first on WyoFile . ...read more read less