Bighorn Sheep Threatened by Livestock

Wild Bighorns Threatened by Domestic Sheep

Should domestic sheep be permitted to graze on public lands when their presence threatens the survival of wild bighorn sheep? That's a question that is increasingly getting serious discussion around the West.

By George Wuerthner, 6-23-09

At one point in my life I was very interested in studying wild sheep. I almost accepted a graduate research project at the U of Alaska to look at winter diet and behavior of Dall sheep in the Brooks Range. I wimped out when I realized that I’d be alone months at a time in a tiny cabin on the North Slope peering through a night vision scope to watch the animals in the near 24 hours of darkness of mid-winter forage in 50 below zero weather. It just didn’t sound like that much fun—though definitely interesting. But for a number of years I read everything I could about wild sheep, and I continue to follow research and news about wild sheep to this date.

Wild bighorn sheep were once fairly common in the western United States and Canada. Some estimates suggest as many as 1-2 million wild sheep once roamed the West. By 1900, over-hunting, habitat degradation and perhaps most importantly disease transmission from domestic sheep to wild sheep had brought the bighorns down to an estimated 15,000. Today there are about 75,000 sheep in the western US and Canada.

While that is a significant growth from its low point, wild bighorn sheep populations are nowhere near their biological potential. There is no doubt in my mind that the West could easily support far more sheep were it not for one thing—domestic livestock.

One thing that was obvious from a study of the literature is that whenever domestic sheep grazing overlaps with wild bighorn sheep, disease frequently decimates the wild animals. So prevalent was this in the scientific literature, I did not think it was controversial—yet as recently as this year the state of Idaho was debating whether domestic sheep were really a threat to wild sheep populations.

The biggest problem for wild sheep is development of pneumonia after contracting Pasturella bacteria from their domestic cousins. Sometimes as many much as 75 percent of the herds may die. For instance, in one study of Hells Canyon, 43 percent of the mortality was due to pneumonia and the researchers believed it was the major limit on bighorn sheep population growth.

Francis Singer and his associates looked at 24 transplanted sheep populations and correlation between persistence and distance to domestic sheep. Not surprising to most wildlife biologists, Singer found that the closer domestic sheep were to wild sheep, the less likely for bighorns to persist. In another study Singer also looked at over 100 bighorn transplants in six western states. Again he found the closer domestic sheep came to wild bighorn, the more likely those sheep were to disappear.

Despite many examples of such die-offs from around the West, the livestock industry and its lackeys in government continue to deny there is any link or at least try to confuse the connection by suggesting there is uncertainty.

This kind of deliberate obfuscation occurred recently when Dr. Marie Bulgin, a University of Idaho professor, and former President of the Idaho Sheep Growers Association, testified before the Idaho Legislature and in federal court that there was no firm scientific link showing domestic sheep transmitted pneumonia to bighorn sheep in the wild. This despite the fact that research on exactly that issue was done in a laboratory she supervised, and indeed, her own daughter participated in the study. There is 1999 story in the Science Daily that discusses research at the U of Idaho that confirms that domestic sheep can be the source of disease transmission.

The fear of disease transmission and subsequent bighorn die-offs has deterred restoration of wild sheep to many areas of the West. For instance, I recall one time in the 1990s when the Montana Fish, Wildlife and Parks Department (MFWPD) proposed to introduce mountain goats to the Centennial Range on the Idaho-Montana border. Goats were never native to the range, but bighorn were. When I wrote the department suggesting that they reintroduce bighorn, they responded by saying that as long as domestic sheep grazed the range, there was little point in attempting any restoration, due to disease concerns. Similar concerns in many other parts of the West have precluded reestablishment of bighorns in native habitat.

There is good reason for this caution. As recently as January 2008, a number of bighorn sheep in Montana’s Elkhorn Mountains by Helena died from pneumonia thought to have been contracted from domestic animals. Other major die-offs in Montana have been reported for bighorn herds in the East Pioneers, Tendoy Mountains, Highland Mountains, Sleeping Giant Area, and Madison Range, as well as elsewhere. There have been several major die-offs of wild sheep in the Hells Canyon area of Idaho and Oregon and in the Sierra Nevada of California. Many other examples could be cited.

Rather than do the obvious, which is to eliminate public land use by domestic sheep, wildlife agencies have taken to killing wild bighorn sheep. Just this past month in Idaho the Idaho Fish and Game shot a ram that was known to mix with domestic sheep along the Salmon River near Riggins. As many as 11 other sheep had contact with that ram and may also be killed. This bighorn was killed in response to a new law passed by the Idaho Legislature that requires Idaho Fish and Game to kill or remove sheep that get near domestic sheep.

Without being forced by the legislature, the Montana Department of Fish, Wildlife and Parks (MDFWP) has adopted a similar policy. For instance, prior to a reintroduction of bighorn sheep to the Gravelly Range on the Beaverhead Deerlodge National Forest near Dillon, MDFWP signed an agreement stipulating that if wild sheep had any interaction with domestic sheep, the wild sheep would be shot—and potentially even entire bighorn herds eliminated.

Disease transmission is only one of the threats posed to wild bighorn sheep by the presence of domestic sheep. Keep in mind there is no free lunch. Domestic animals consume forage that would otherwise support native species like wild bighorn sheep. This forage competition can stress wild sheep, making them more vulnerable to disease or starvation.

Also domestic livestock grazing (including cattle) have frequently altered plant communities to favor browse species desired by mule deer, whose populations sometimes increase and provide alternative prey to support higher populations of mountain lions, which can prey on bighorn sheep. Since many bighorn herds are small and isolated, even the loss of a few animals to predators can hurt wild herd survival. While predators get the blame, the ultimate source of the conflict lies with domestic livestock.

This naturally raises the question of why domestic animals grazed on public lands have preference over wild bighorn sheep. Why not just close the domestic sheep allotments so that wild animals are given priority?

Only a few environmental groups are willing to take on the Western myth. The Idaho-based group Western Watersheds is one of the most persistent critics of the livestock industry and has sued the Forest Service in Idaho and Wyoming over the management of wild bighorn and domestic livestock—arguing that the agency should keep domestic animals away from wild herds, and should even close allotments if necessary. (In the interest of disclosure, I am an advisor to WWP).

Recently in Montana, the Gallatin Wildlife Association (I am a member) is requesting that the Beaverhead Deerlodge National Forest close down sheep grazing allotments in the Gravelly Range and Snowcrest Ranges to safeguard wild sheep. The Center for Biodiversity (I am an ecological advisor) is also working to protect wild sheep from their domestic cousins in California.

I am convinced that as long as domestic sheep are roaming our public lands, wild bighorn sheep will never reach their biological potential. And that is a loss not only to hunters, but to the public at large who could be enjoying restoration of bighorn herds throughout the West.

The real issue is larger than wild bighorn sheep. Whether it is bighorn sheep, bison, grizzly bears, wolves, cutthroat trout, prairie dogs, or sage grouse, if private business (i.e. livestock production) threatens public wildlife on public lands, shouldn’t the private businesses be the ones that ought to go?