Domestic Sheep Threaten Wild Bighorns

Rocky Mountain Bighorn Sheep Ram. Photo George Wuerthner

Bighorn sheep acquired their name for the large circular horns of the mature rams. They are strongly associated with mountain terrain, particularly steep hills and cliffs, which protect them against predators. They graze upon grasses and other plants. In general, bighorns are associated with drier parts of the West where they can obtain their forage, even in winter.

Bighorn sheep distribution

Bighorns tend to be found in regions with limited snowfall like deserts or places where snow does not accumulate like windy ridges. For instance, bighorn sheep in Montana’s Absaroka Beartooth Wilderness and Wyoming’s Absaroka Range, and the Wind River Range all winter at 10,000-12,000 feet. At these elevations, they survive on south-facing slopes and wind-blown mountain tops.

Bighorns range where snow depth is shallow enough to permit winter grazing on grass. Photo George Wuerthner 

Bighorn sheep once numbered in the hundreds of thousands across the West. Osborn Russell, a fur trapper who traveled widely across the Rocky Mountain West in the 1830s, observed “thousands” of bighorns in the Absaroka Mountains in what is now Wyoming.

Bighorn sheep ranged from British Columbia and Alberta south to Mexico and were divided into various subspecies, based mainly on geography.

Bighorn sheep numbers declined dramatically after the settlement of the West. Between market hunters who killed the animals to supply mining camps with fresh meat to trophy hunters who wanted to garner status for their hunting exploits, the bighorn numbers declined over time, including the extinction of at least one of the subspecies—Audubon’s Bighorn—which once roamed through the badlands of North and South Dakota. The California Sierra Nevada bighorn sheep are rare enough to be listed as endangered under the Endangered Species Act.

However, the real threat to bighorn sheep came not from the hunter’s guns but domestic sheep. Starting in the late 1800s and continuing into the 1900s, domestic sheep were grazed in vast herds of thousands of animals across the public domain. They typically mowed down the vegetation upon which wild bighorns depended. They were the “hooved locust” that John Muir experienced in the Sierra Nevada. I, myself, have witnessed the same destruction of vegetation after the passage of a domestic sheep herd.

Domestic sheep grazing on the Helena-Lewis and Clark National Forest, Montana. Photo George Wuerthner

Weakened by lack of food consumed by the wandering domestic sheep bands, wild bighorns were also susceptible to disease, particularly pneumonia, carried by domestic animals. Infectious pneumonia can result in a 90% reduction in a herd’s numbers. Any survivors tend to show poor lamb recruitment and survival for years, adding to herd viability loss. Numerous isolated sheep herds winked out across the West due to die-offs induced by contact with domestic sheep.

The introduction of sheep often led to bitter wars between cattle ranchers and sheepmen. Part of the animosity was because sheepmen often migrated around public lands, wintering in lowlands and then moving their sheep bands into the high country for summer pasture. Once a sheep herd passes over rangeland, there was often nothing left for any other animals, including domestic cattle.

In response, the politically powerful cattlemen lobbied the government to stop what they considered the “stealing of their forage.” The result was the 1934 Taylor Grazing Act which created the Grazing Bureau to administer public land grazing. The bureau set up “grazing allotments” based on “base property.” Since cattlemen tended to have a base ranch compared to the migratory sheepmen, the law favored cattle grazers over sheep grazed. The Grazing Bureau would later become the Bureau of Land Management.

Domestic sheep numbers peaked at 55 million during the 1940s and 1950s and have declined since then. Many former sheep ranchers eventually switched to cattle production for economic reasons.

During the rut, rams will wander widely seeking mates and often come into contact with domestic sheep. Photo George Wuerthner

Nevertheless, domestic sheep still pose a significant threat to wild bighorns. During the fall rut, bighorn rams wander widely looking for mating partners and sometimes encounter domestic sheep herds. It often only requires a short interaction with domestic animals for the wild bighorn to become infected with pneumonia, then when they return to the herd, they bring the disease with them to infect the rest of the animals.

Tendoy Mountains from Mt Garfield, Beaverhead Deerlodge National Forest, Montana is typical of bighorn preferred habitat of arid mountain ranges with light snow cover in winter. Photo George Wuerthner

It has become common practice to kill wild bighorns if they exhibit the disease’s symptoms or are known to have mingled with domestic sheep. In at least one instance, an entire herd of bighorns was shot in the Tendoy Mountains of Montana in 2015 to remove the wild sheep, to reintroduce non-infected sheep into the habitat (which was recently done in early 2021).

Sheep grazing Eureka Basin Gravelly Range, Beaverhead Deerlodge National Forest, Montana Photo George Wuerthner

In 2004, the Montana Dept of Fish, Wildlife, and Parks, before it reintroduced bighorns to the Gravelly Range in Montana, agreed to shoot any bighorns that even roamed close to domestic animals that graze public lands on the Beaverhead-Deerlodge National Forest.

Similar policies are now practiced around the West. For instance, recently, the Washington Department of Fish and Wildlife (WDFW) killed a dozen bighorn sheep to prevent the potential spread of disease.

What is truly ironic about these policies is that wild bighorns suffer so that domestic sheep owners can graze their herds on public lands.

The Centennial Mountains is the location of the USDA Sheep Station which has precluded any transplant of wild bighorn due to disease transmission fears. Photo George Wuerthner

Worse, domestic sheep’s mere presence often means vacant and suitable bighorn habitat is left empty for fear that any transplants will fail if domestic sheep are present. For instance, back in the 1990s, the BLM considered bighorn sheep restoration for the Centennial Mountains on the Montana Idaho border. Due to the USDA Sheep Station’s presence, it decided not to proceed further with this idea.

In 2007, lawsuits brought by the Western Watersheds Project, Hells Canyon Preservation Council, and Wilderness Society against the Bureau of Land Management and later the Forest Service argued that public lands agencies must protect the bighorns. Since then, other groups have also challenged the BLM and Forest Service over domestic sheep grazing in bighorn habitat, including the Gallatin Wildlife Association, Center for Biological Diversity, Wild Earth Guardians, among other organizations.

As a result of legal cases, the Forest Service determined that the only way to prevent transmission of diseases from domestic animals to wild bighorn sheep was to maintain a physical distance. Both the Forest Service and BLM subsequently adopted this model in theory, though they frequently do not implement it.

Hells Canyon on the Idaho-Oregon border, where bighorn sheep herds have suffered repeated die-offs from disease transmitted from domestic sheep. Photo George Wuerthner

The original legal case brought by the Western Watersheds Project against the Payette National Forest resulted in the closure of 70 percent of the forest to domestic sheep grazing, following a court-ordered analysis under the National Environmental Protection Act. The Forest Service analysis determined that best management practices are not sufficient to prevent contact and disease transmission.

Subsequently, the Idaho Sheep Growers Association challenge in the 9th District Court of Appeals failed. The courts upheld the Forest Service decision to close any allotments that threaten wild bighorn sheep. However, many national forests have been reluctant to antagonize sheep owners. Instead, in far too many instances, the agency fails to remove domestic animals from public lands where they can interact with wild bighorn sheep. And Fish and Game departments continue to shoot wild bighorns to prevent further infections and loss of herds.

Yakima River in Washington. Photo George Wuerthner 

As recently as 2020, new outbreaks of pneumonia have been detected in wild bighorn herds in the Cleman Mountain herd of bighorn sheep, located primarily in the Okanogan-Wenatchee National Forest northwest of Yakima. At nearly the same time, the Oregon Department of Fish and Wildlife announced the detection of pneumonia in the Burnt River herd near Baker City.

A case brought by Advocates for the West on behalf of Western Watersheds Project and Wild Earth Guardians is challenging the Okanogan-Wenatchee NF failure to close sheep allotments near the wild bighorn herds. Despite much evidence that these domestic sheep allotments present a severe threat to the bighorns, the Okanogan Wenatchee NF has continued to authorize domestic sheep grazing every summer.

This map shows the close location of bighorn sheep herds (yellow) and domestic sheep allotments near the Yakima River on the Okanogan Wenatchee NF, Washington. 

The federal government has the right and is obligated to protect bighorn sheep by the closure of grazing allotments. However, in some instances, voluntary grazing allotment buyouts have hastened the removals. Under these agreements, a public lands grazing permittee will waive back their grazing privileges (grazing is a privilege, not a right on public lands) to the federal government in exchange for a previously agreed upon payment by private foundations or individuals.

It’s time to stop shooting the public’s bighorn sheep to accommodate the private use of public lands by sheep growers. The shooting bighorns is similar to the government policy of killing predators on public lands to modify livestock producers. It’s time to put the public interest first. Hopefully, we won’t have to file lawsuits on every federal agency across the West to get them to manage OUR lands for the benefit of all citizens. But until that time, thankfully, groups are willing to challenge the agencies’ preference for domestic animals over wild ones.



  1. cynthia brown Avatar

    Please stop killing the BigHorn Sheep they ae part of our history and should be presved and saved by our history

  2. Rene Rowland Avatar
    Rene Rowland

    The sheep are not a threat. It’s the humans that breed and graze them.

  3. Maggie Frazier Avatar
    Maggie Frazier

    This is another instance (among many) of “culling” wild animals in order to pacify livestock corporations! As George said, the killing of predators, also the slaughter of buffalo in order to “protect” cattle. Frankly, if it continues to be necessary to allow livestock grazing on public lands & forests, seems to me its time to vaccinate sheep against pneumonia AND cattle against brucellocis! The DOMESTIC LIVESTOCK, that is.
    After all, I’m sure most ranchers vaccinate against other diseases already. It should be their responsibility to protect THEIR animals.

  4. Jim Holyan Avatar
    Jim Holyan

    I think there should be a tip of the hat to the Nez Perce Tribe for initiating the work that led to the Payette NF’s sheep allotment closures. Their study, along the main stem Salmon River upstream of Riggins, was directly responsible for the implementation of those restrictions/closures.

  5. Ida Lupine Avatar
    Ida Lupine

    The bighorn sheep are such magnificent animals, we simply cannot lose them. They are part of the native wildlife of this continent. I hope that means something to people.

  6. Charles Jennings Avatar
    Charles Jennings

    I wish the USFS would allow placing Selenium blocks again in the whiskey Mountain region. I fear that the bighorn Sheep are so malnourished that they are susceptible to disease. Plus, I can’t believe that federal and state wildlife officials are collaring lambs as young as one day old. I imagine that their cortisol levels are spiking due to stress, thus compromising their immune system when in turn brings on the pneumonia. I don’t believe that the Whiskey Mountain herd is nutritionally healthy like it once was and that they need supplementation of nutrients into their diet. Otherwise, herd numbers will continue to decrease. There are thriving herds in surrounding states, even when carrying MOVI pathogens.

  7. David Hoefer Avatar
    David Hoefer

    I am ashamed that the agency I worked for, USFS, usually caves in to the domestic livestock grazers. Politics play a big role in the power of the grazers when Forest Plans and laws favor livestock removal. Even on the Sawtooth National Recreation Area, livestock grazing is permitted when it is direct conflict to the law. Someday grazing will become on most public lands will unprofitable, well hopefully.


George Wuerthner is an ecologist and writer who has published 38 books on various topics related to environmental and natural history. He has visited over 400 designated wilderness areas and over 200 national park units.

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George Wuerthner