Pneumonia hits western bighorn herds

Over the past year, bighorn sheep in 11 herds in Montana, Nevada, Washington, Wyoming and Utah caught pneumonia. More than 1,000 — or about half in the affected herds — succumbed or were culled, with Montana alone losing about 10 percent of its bighorns. The vector? In two cases, bighorns had mingled with domestic sheep or goats; in most others, it was at least a possibility. Domestics carry microorganisms known to cause pneumonia in their wild cousins, which disease and other factors have reduced to a fraction of their historic numbers. Decades of research suggest letting the two species mix is disastrous. Still, many sheep ranchers argue that transmission isn’t well enough understood to warrant drastic action. In a study published this summer, though, Washington State University researchers demonstrated conclusively that bighorns picked up lethal pathogens from domestic sheep. The findings add momentum to a recent wave of concern over the West’s bighorns — one that has led federal agencies to be more proactive about separating them from domestic sheep on public land. For four years, the Western Association of Fish and Wildlife Agencies has convened the Wild Sheep Working Group to help coordinate policy between the feds, states, NGOs and ranchers. Meanwhile, the Forest Service’s Rocky Mountain and Intermountain Regions recently listed bighorns as sensitive species, mandating extra scrutiny for projects that could affect them. Both the Forest Service and Bureau of Land Management are updating their general bighorn policies...more