April 12, 2023 | By:

Expansion and Restoration of Bison to Greater Yellowstone Ecosystem

Yellowstone bison are a globally unique animal. Harsh winters can drive bison out of the park where they are often killed. (Photo: George Wuerthner)

Yellowstone bison are a globally unique animal. Harsh winters can drive bison out of the park where they are often killed. (Photo: George Wuerthner)

Yellowstone’s bison are unique, essentially influenced by natural evolutionary processes since the Park’s early days. Today the herd has grown to approximately 6,000 animals. Still, the ability of these bison to migrate out of Yellowstone National Park is severely limited by hunting, capture, and slaughter practices.

Since 1985 nearly 10,000 Yellowstone’s bison have been killed or removed from the park ecosystem.

Gut piles are left behind that poison eagles and other scavengers who ingest the lead bullets.

Gut piles are left behind that poison eagles and other scavengers who ingest the lead bullets.

The biggest obstacle facing Yellowstone bison is the freedom to roam. Unlike all other wildlife in the Park, bison are systematically slaughtered when they attempt to migrate north of the Park near Gardiner, Montana.

The current bloodbath severely affects Yellowstone’s bison evolution and genetic diversity—at least 1200 bison have been killed so far this winter.

Yellowstone’s founding population of 25 bison means the herd has gone through at least one genetic bottleneck. The periodic removal of bison by slaughter further reduces this genetic diversity, providing to the problem of genetic drift and the increase of maladaptive alleles in the bison population.

This genetic bottleneck is further complicated by bison being tournament breeders, meaning one bull may contribute to the genetic makeup of many offspring.

The heads of bison killed by tribal hunters adjacent to Yellowstone NP. (Photo: George Wuerthner)

The heads of bison killed by tribal hunters adjacent to Yellowstone NP. (Photo: George Wuerthner)

Also, the annual killing of bison eliminates the animals most inclined to migrate. Bison, as herd animals, transmit “cultural knowledge” across generations about where to migrate, how to avoid predators and other survival information. Over time this selective factor could reduce bison’s natural mobility tendencies if it hasn’t already.

Bison slaughter is taking food out of the mouth of the Park’s native wildlife. Hunting and slaughter remove bison carcasses availability from Yellowstone’s other wildlife, from scavenging ravens to grizzly bears. As Bozeman conservationist Phil Knight has characterized it, the slaughter is a strip-mining of the Park’s biomass.

Notably, nearly all bison herds outside of Yellowstone have been domesticated, with many possessing various degrees of cattle genes, including bison in Yellowstone. Most bison in the lower 48 states are found on private ranches where they are managed like livestock.

There are only 17 conservation herds with approximately 17,000 animals. But even these “conservation herds” are managed in multiple ways that results in domestication of them, including annual population reductions (aka, National Bison Range, for instance).

The Yellowstone bison are the least compromised of all bison found in the United States. While early management emphasized feeding and protecting the few remaining bison, for the most park, the Park’s bison were shaped by natural evolutionary processes like predation, drought, harsh winters, disease, and other factors that shape the genome.

James Bailey has written a book American Plains Bison: Rewilding an Icon arguing for preserving Yellowstone’s unique genetic traits and maintaining wildness as an essential trait.

He argues effectively that the genetic composition of all our bison has been and is being changed by six processes: 1) continental and local founder effects limiting genetic diversity to that of very few animals; 2) crossbreeding with domestic cattle genes; 3) inbreeding; 4) genetic drift; 5) artificial, human-determined selection; and 6) natural selection.

Together, the first five weaken or replace natural selection, especially in commercial bison herds where domestication is underway. But all five processes exist in our conservation herds of bison as well.

Tribal members butcher a Yellowstone bison killed just outside of Yellowstone National Park. (Photo: George Wuerthner)

Tribal members butcher a Yellowstone bison killed just outside of Yellowstone National Park. (Photo: George Wuerthner)

The domestication of most non-park bison herds makes the Yellowstone bison even more unique and of global significance. The fact that they are slaughtered regularly by public agencies and/or tribal hunters, even if the animals are eaten, would be analogous to cutting down centuries-old redwoods to build decks.

Part of this debate concerns the state of Montana’s brucellosis policy, which limits the movement of bison outside of the Park due to fears that bison can transmit the disease to livestock. This disease transmission fear is primarily a bogus argument since elk can move freely and have transmitted brucellosis to livestock but are not shot or limited to Yellowstone Park.

In the past few decades, while there has been an overall decline in elk wintering in the Park, bison numbers have increased.

There are concerns that the current Park bison population of 6,000 is too high, with some range ecologists suggesting the high numbers are harming the vegetation, particularly in the Lamar Valley. Some suggest bison were never abundant in the Park proper, though regionally abundant outside of the park. Richard Keigley makes a case that prior to the 1840s bison did not exist in any numbers in the park. However, this conclusion is based on the limited number of primary sources, basically Osborn Russell, who traversed Yellowstone a number of times between 1834-1838 and did not report bison. Nevertheless, Keigley’s paper contains quite a bit of good historical background on Yellowstone bison.

For instance, the Lewis and Clark expedition on its return trek traveled across the Gallatin Valley (where Bozeman today is located) and William Clark reported bison “roads” running “in every direction.” Sacagawea who was with Clark told him that her people (Shoshone) had had a local hunting impact on buffalo driving them out of the valley.

Similar reports for bison abundance in the region surrounding the Greater Yellowstone Ecosystem were reported by traders and fur trappers. There would appear to be no reason why at least small numbers of bison would not have seasonally migrated into what is now Yellowstone National Park. For instance, in 1866 prospector Bart Henderson mentions encountering “thousands” of bison along Buffalo Creek just north of the park in what is now the Absaroka Beartooth Wilderness.

At least early observations suggest that bison were present, though perhaps not as abundant as found today. As Park Historian Lee Whittlesey observed, “The historical record suggests that bison were there all along and in good numbers.”

The second superintendent of Yellowstone Philetus Norris reported in his 1877 annual report that “nearly 2000 hides of Rocky Mountain Elk, nearly as many each of bison deer and antelope, and scores of not hundreds of moose and bison were taken out of the park in the spring of 1875, probably 7000, or an annual average of 1000 of them, and hundreds if not thousands of each of these other animals have been thus killed since its discovery in 1870.” He goes on to note that in the eastern portion of the park:  “there is still a herd of three hundred or four hundred of the curly nearly black bison or mountain buffalo.”

Bison herd in Lamar Valley, Yellowstone National Park. (Photo: George Wuerthner)

Bison herd in Lamar Valley, Yellowstone National Park. (Photo: George Wuerthner)

For a more complete review of wildlife observations, see Lee Whittlesey and Sarah Bone’s The History of Mammals in the Greater Yellowstone Ecosystem 1796-1881 and companion The History of Mammals in the Greater Yellowstone Ecosystem 1796-1881: A multi disciplinary Analysis of Thousands of Historical Observations Vol. 2. These historians documents 475 bison observations early in the park history, however, only 4 were within the park boundaries during the early period.

Nevertheless, it’s important to note that there were virtually no travelers to record wildlife observations in what is now Yellowstone Park until the 1870s.

One of the first places in the West where bison were extirpated by Indian hunting was in Southeast Idaho and adjacent parts of northern Utah, western Wyoming, and southwest Montana. By 1840, according to Yellowstone Park historian, Lee Whittlesey, bison were essentially gone from this region where they had once been relatively abundant. (See map of bison distribution.)

With the demise of the regional bison population, almost entirely due to Indian hide hunting,  tribes like the Bannock began to make annual treks to hunt bison on the plains starting around 1838, and at least some of the time, they traveled through what is now Yellowstone Park. Whittlesey speculates that tribal hunting in what is now the park may have reduced bison within what is now Yellowstone.  Unfortunately, we have no way to confirm or deny this speculation since there were no written reports about what is now Yellowstone Park  this early except for a few journals like those of Osborn Russell.

The debate centers on how many bison are appropriate in Yellowstone.

Yellowstone Park staff suggest that bison are ecosystem engineers shaping the Park’s vegetation and that the Park could sustain as many as 10,000 bison. A good book on Yellowstone bison is Yellowstone Bison: Conserving an American Icon in Modern Society.

I won’t go into the nuances of this debate, but I will mention a couple of points to consider. There are valid concerns on both sides of this debate.

However, when the Park was established, the climate was considerably colder and snowier. It was the tail end of the Little Ice Age, so the capacity of what is now Yellowstone to sustain any large ungulate herds year-round was likely lower in the 1800s than at present.

Bison migrating through Roosevelt Arch entrance at Gardiner, Montana. (Photo: George Wuerthner)

Bison migrating through Roosevelt Arch entrance at Gardiner, Montana. (Photo: George Wuerthner)

In the pre-settlement era, wildlife, including elk, bison, and pronghorn, were not restricted to the park boundaries and could easily migrate to lower-elevation winter ranges outside of what is now Yellowstone Park.

Archeological evidence shows that bison occasionally roamed higher elevations of the Greater Yellowstone Ecosystem. Still, this use of high country varied with climate, as did the human population dependent upon them. For instance, during a particularly drought period about 7,000 years ago, archeological evidence for human use of Yellowstone increased significantly but declined with cooler temperatures. So the temporal period is critical to understanding both wildlife and human history in what is known as Yellowstone.

There is no doubt that bison utilized high country at least seasonally throughout the ecosystem. I have found bison tracks and dung at elevations of over 10,000 feet in the North Absaroka Wilderness along Yellowstone’s eastern border, so it’s not inconceivable that bison utilized all available habitat in the pre-settlement era from lower elevation snow-free winter range to alpine meadows.

Part of this debate on the appropriate number of Yellowstone bison should focus on where the animals are found. In other words, there is more habitat for bison within Yellowstone that is currently unused such as the extensive meadows in the Bechler region, though given the heavy snowfall in that portion of the park, bison would likely have to migrate outside of the park to survive the winters. However, even if bison were able to colonize all these nooks and crannies, it eventually would exceed the Park’s capacity to sustain bison.

Tribal members have killed hundreds of bison as they seek to migrate to snow-free areas near Gardiner, Montana. (Photo: George Wuerthner)

Tribal members have killed hundreds of bison as they seek to migrate to snow-free areas near Gardiner, Montana. (Photo: George Wuerthner)

Even with the expansion of habitat use within the Park, there is a desperate need to expand Yellowstone’s bison numbers and distribution. The best way to accomplish this is to foster the recolonization of suitable habitats throughout the Greater Yellowstone Ecosystem (GYE).

One way to reduce the grazing impacts that some researchers observe, while still preserving the genetic and evolutionary  traits of Yellowstone bison, is to expand the landscape available to them so they are not bottled up behind the artificial line of the park border. Reestablishing migratory movement is critical to addressing both concerns.

We must consider restoring bison across the Greater Yellowstone Ecosystem and other larger public lands entities like the Charles M. Russell National Wildlife Refuge (CMR) in Montana. To learn more about the potential for bison restoration along the Missouri River/CMR, see the Wild Bison Coalition.

Notwithstanding the numerous opportunities to establish native wild bison in other parts of the West like the Charles M. Russell NWR, there is equal opportunity to expand bison herds in the Greater Yellowstone Ecosystem to create a “meta-population” of linked herds. Such a meta-population would be sufficiently large enough to reduce the problems of inbreeding depression, random genetic drift, and other issues associated with smaller populations.

The area north of Gardiner, Montana, lies in a rain shadow of the Gallatin Range. Annual precipitation is approximately 11 inches, less than Tucson, Arizona, while precipitation of 70 inches (translating into many feet of snow) has been recorded on Yellowstone’s Pitchstone Plateau.

While snow may be piled 2 feet deep in Bozeman, there is often no snow at all at Gardiner, even though it exists at a higher elevation than Bozeman. Indeed, in the 1930s, agricultural lands north of Gardiner were added to Yellowstone to increase the winter range. So, expanding the park boundary to accommodate wintering wildlife is not new.

Bison in snowstorm, Blacktail Plateau, Yellowstone National Park, Wyoming (Photo: George Wuerthner)

Bison in snowstorm, Blacktail Plateau, Yellowstone National Park, Wyoming (Photo: George Wuerthner)

The “tolerance” area for bison north of Yellowstone Park is currently limited. This tolerance area could be expanded northward by approximately 20 miles, to include Tom Miner Basin, Dome Mountain, the Dome Mountain State Wildlife Management Area, and adjacent Custer Gallatin National Forest areas. Enlarging the tolerance area would significantly open up much-needed lower elevation winter range for bison use.

One way to accomplish this would be to legislatively “expand” Yellowstone Park north of Yankee Jim Canyon to include lands currently managed by the Custer Gallatin National Forest. Indeed, a good argument could be made that the entire Greater Yellowstone Ecosystem should come under the NPS management since it is one of the few temperate ecosystems that is still relatively intact, thus of global significance.

Other legislative proposals like the Northern Rockies Ecosystem Protection Act that would designate wilderness status for all roadless lands surrounding Yellowstone are also a step in the right direction.

Some bison survive the winter by frequenting Yellowstone’s thermal basins, where snow is lower, and temperatures can be warmer. (Photo: George Wuerthner)

Some bison survive the winter by frequenting Yellowstone’s thermal basins, where snow is lower, and temperatures can be warmer. (Photo: George Wuerthner)

However, even without legislation, many other parts of the Greater Yellowstone Ecosystem could sustain small to medium bison herds. Connectivity between these herds would be necessary to ensure long-term genetic diversity preservation. Collectively these herds could comprise a metapopulation of thousands of bison.

Many of the following areas are high-elevation regions, with snowy and harsh winter conditions, but similar to the existing bison habitat in Yellowstone National Park.

Among the prominent areas that could sustain bison recolonization are the following areas:

  1. Hebgen Basin/Upper Gallatin River and adjacent tributaries, Montana. The area from Big Sky south to West Yellowstone has numerous sites, like the Taylor Fork in the Madison Range and the Buffalo Horn-Porcupine area of the Gallatin Range, suitable for bison recolonization.
  2. Island Park/Sand Creek, Idaho. The Island Park area and adjacent Sand Creek Wildlife Area could provide a migratory bison herd’s summer and winter habitat.
  3. Centennial Valley/Gravelly Range/Snowcrest Range, Montana. This area to the West of Yellowstone NP has substantial public land holdings, including Red Rock Lakes NWR, and significant proposed wilderness in the Centennial Mountains, Gravelly Range, and Snowcrest Ranges. In addition, several state wildlife management areas like the Robb Ledford WMA exist.
  4. Mount Leidy Highlands/Teton Wilderness/Gros Ventre River/Wilderness, Wyoming. A small bison herd already exists in Grand Teton National Park. Expansion of this herd’s habitat use to the mountains east of the Tetons would permit a much larger population to utilize the area. Overall, this is snowy country, and the size of any herds would naturally be limited by harsh winters.
  5. Upper Shoshone/Greybull Rivers, Bighorn Basin, Wyoming. These rivers that flow eastward off the Absaroka Mountains lie in the “rain shadow” of the peaks and thus tend to have shallow snow conditions that could sustain wintering bison.
  6. Clark Fork of the Yellowstone/Pryor Mountains/Bighorn NRA, Montana/Wyoming. This region lies in the lee of the Beartooth Mountains, which exceed 12,000 feet. Consequently, one of the most arid locations in all of Montana and adjacent Wyoming is found in this area.

Indeed, the lower elevations of the Pryor Mountains and adjacent Bighorn NRA are sometimes called Montana’s Utah due to the red rock/limestone geological features. The area is mainly snow-free in winter but with access to much higher summer pastures in mountain areas like the Pryor Mountains.

  1. Union Pass-Upper Green River, Wyoming. The Union Pass/Upper Green River/Red Desert is a second Lamar Valley in terms of wildlife potential. The area is already home to elk, pronghorn, grizzlies, wolves, and moose. The only large mammal it lacks is bison. The Upper Green River was once the location of extensive bison herds documented by many fur traders and trappers in the 1820-the 1840s. Restoring bison to this region would permit migration southwards from the high country in the Wind River and Gros Ventre Ranges into the Red Desert area. The Red Desert is the largest unfenced area in the western US.
  2. Gray’s Lake/Salt River Valley/Bear River, Idaho. This part of the GYE sustained large bison herds in the past, and could once more.

If bison could be established throughout the Greater Yellowstone Ecosystem as one meta-population, it would preserve much of this population’s evolutionary and genetic diversity.

Increasing bison numbers across the Greater Yellowstone Ecosystem would have other ecological benefits.

For instance, weak or dead bison numbers would increase across the landscape, making them available to predators like grizzly bears and wolves, substantially increasing overall survival. To a sow grizzly with cubs finding a dead bison in the spring is like winning the lottery; it is an abundance of high-quality food at a time when other sources of sustenance are limited. For instance, Yellowstone’s grizzlies eat more meat than almost any bear subpopulation. In the past, this was primarily elk. However, an increase in bison would provide a substantial additional food resource when other dietary options like whitebark pine nuts are declining.

Although not my intent, if bison numbers across the ecosystem were substantially increased, limited hunting by tribal people and others could conceivably be instituted without harming the overall bison genotype or evolutionary behavior.

Bison herd in Yellowstone National Park. (Photo George Wuerthner)

Bison herd in Yellowstone National Park. (Photo George Wuerthner)

One obvious obstacle to the recolonization and restoration of bison across the Greater Yellowstone Ecosystem is the presence of domestic livestock on public lands. Bison dietary preferences are similar to cattle, and no doubt, beyond even the alleged fear of brucellosis transmission, livestock producers do not relish the idea of forage competition between bison and cows.

The best way to alleviate this competition for public forage is to remove domestic livestock from all proposed bison restoration areas. Although grazing on public lands is a privilege, not a right, the political influence of the livestock industry makes any reduction in livestock grazing difficult.

The Voluntary Grazing Permit Retirement Act entices ranchers to abandon public lands grazing lands. The proposal would pay ranchers to give up grazing privileges in exchange for an agreed-upon cash payment.

Other potential problems that could be foreseen are the issue of bison movement through fences or the occupation of private lands. These issues can be dealt with case-by-case, including lease agreements with ranchers to tolerant bison grazing or movement across private lands. Such an agreement was negotiated with the Church Universal and Triumphant Church (CUT), who own significant lands just north of Yellowstone near Gardiner.

Groups that are advocating for restoration of wild bison including Yellowstone Voices,  Wild Bison Restoration CoalitionRoam Free NationAlliance for Wild Rockies, and the Gallatin Wildlife Association. Yellowstone Voices, in particular, has videos of the on-going bison slaughter so one can see first hand how our national mammal is being treated.

Restoring Yellowstone bison to the entire Greater Yellowstone Ecosystem is a worthwhile project analogous to restoring wolves, grizzlies, and other wildlife. We can repair what was previously degraded and diminished to the ecosystem by restoring bison across the landscape. It’s time to get started.

This post was published first in The Wildlife News.

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Jeff Hoffman
1 year ago

There is something essentially wrong with humans in that they have some insatiable urge to kill every large animal they see. When humans began leaving Africa 60-90,000 years ago, they caused extinctions everywhere they went by just killing everyone they saw. That’s not at all my reaction to seeing wildlife and I can’t relate to that, but it’s how most people are. A friend in Arizona took me to the Superstition Mountains, and we saw a Gila monster. My friend’s reaction was to stop the car and chase the poor animal, which at some point turned around and hissed at him before escaping down the cliff (didn’t fall, so happy ending). Urban people don’t seem to be like that as much, but they don’t see much if any wildlife either.

Zach Finn
1 year ago

It’s not cool to try to paint “tribal members” in a bad light for hunting bison, an activity for food procurement they have done for millenia. This is colonization in conservation in action.

Is it not true that more culls are performed by European-descended people?

1 year ago

It’s my certain belief the reason we have so many disturbing problems in our natural world is that there are just too many human “critters” on our planet and yet there seems to be no humane and gentile way to significantly reduce our human population in time to make the needed differences. And, of course my concerns are related to saving the natural world and as such ALL wildlife and all living creatures. I recently read an article that after the Europeans (the “Whites”) came to America we proceeded to wipe out 90% of the native Americans….so, we really know how to slaughter all kinds of living creatures

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