Nonnative weeds threaten to choke out native grasses on Missoula’s open foothills, so sheep were put to work on Mount Jumbo’s leafy spurge. Unfortunately, Missoula’s wooly alternative endangers one native species that has surprisingly few places left to roam.

On Tuesday, conservation groups released a report showing that 85 percent of Montana’s wild sheep herds are at risk of disease due todomestic sheep, including those on Mount Jumbo. The National Wildlife Federation, Montana Wildlife Federation, Wild Sheep Foundation and Montana Wild Sheep Foundation sponsored the report.

Domestic sheep are accustomed to certain bacteria in their noses, but those same bacteria can cause deadly pneumonia in wild sheep. Close proximity of domestic sheep partly explains why wild-sheep herds often experience population crashes. For example, the herd in the Rock Creek valley east of Missoula had more than 200 sheep until nearby domestic sheep prompted a 2009 pneumonia outbreak that cut the wild population in half.

While wildlife agencies have long known that contact with even one domestic sheep can be disastrous for a wild sheep herd, conservation groups wanted to identify which Montana herds are actually at risk. They decided to do their own study after watching the U.S. Forest Service conduct similar risk-of-contact analyses for sheep-grazing allotments in Idaho, Wyoming and Utah, said Tom France, National Wildlife Federation regional executive director

Wild sheep herds don't stray far from their home turf. But young rams will wander farther afield to find mates. If they come in direct contact with domestic ewes, they can carry deadly bacteria back home to the herd.

The report investigators looked within a 20-mile radius of each herd’s territory and found that domestic sheep are too close for 39 of 46 herds.

“The scale of the threat startled us, because Montana has a lot of bighorn herds and to think that that many of them might be compromised we thought was newsworthy,” France said. “Just sitting back and doing nothing is not good for bighorn conservation, so how do we collectively take additional steps to reduce the risk?”

In other states, domestic sheep using federal grazing allotments make up a bigger portion of the problem for wild sheep. In Montana, private ranches and a few sheep on small independent hobby farms scattered across the landscape are the bigger threats.

While public-land grazing allotments affected 18 of Montana’s wild sheep herds, private production lands affected almost twice as many herds and hobby farms affected 26, according to the study.

The Montana Wool Growers Association has worked with Montana Fish, Wildlife & Parks and groups such as the NWF to retire grazing allotments and to come up with solutions for bighorn sheep. But the MWGA has no pull with small farm owners who don’t belong to the association, said MWGA attorney James Brown in a 2014 interview.

Finally, weed-control projects that use sheep, such as the one on Mount Jumbo, threaten to impinge on nine wild herds, including one east of Bonner. Local hunters have often been angered when wild sheep have been killed after coming into contact with the weed-eating sheep.

Hunters have also become frustrated with FWP’s efforts to restore or transplant wild herds, but the disease problem is daunting.

FWP’s wild sheep plan set a goal of creating 10 new herds by 2020, but the agency has struggled to find suitable habitat far enough away from safe domestic herds. The plan has more rigorous standards than the NWF report, requiring that no domestic sheep be within 14 miles of where wild sheep are introduced. A plan to transplant wild sheep into the Bridger Mountains east of Bozeman is still on hold because a couple small producers within that distance refuse to install fencing to keep wild sheep out.

Meanwhile, the agency is eradicating a small herd that has struggled with pneumonia in the Tendoy Mountains. Biologists plan to transplant new animals into the area, but the situation that caused the pneumonia in the previous animals will still exist.

“Our mission is to put and keep sheep on the mountain, which means raising and spending millions of dollars of private money to translocate sheep, and trying to keep them healthy following release,” said Kevin Hurley, conservation director of the Bozeman-based Wild Sheep Foundation Conservation.

Frustrated, a Bozeman group recently sued the U.S. Forest Service in an effort to rescind sheep-grazing allotments to free up habitat in the Gravelly Mountains, southeast of Ennis. However, France doesn’t encourage court action as a method to correct the domestic-wild sheep overlap.

“We think that this needs to be a much more collaborative effort. We felt like we have had good success working with permittees who want to do something else. We think that kind of thing will put us on a more resilient path,” France said.

The report recommends more outreach and education, especially for hobby farmers and 4-H groups; incentives to minimize contact between private flocks and wild sheep; and voluntary retirement of allotments or conversion to cattle grazing. And in the case of Mount Jumbo, the report recommends developing more multi-pronged approaches for weed control.