A family group of grazing bison move through the fog in Yellowstone. Descended from ancestors who survived near extinction, park bison face ongoing intolerance in Montana based on the disproven premise that they represent the most serious threat of spreading brucellosis to private cattle herds outside Yellowstone. There has never been a documented case of Yellowstone bison spreading brucellosis to cattle. A report from the National Academies of Sciences concluded the most serious threat of wildlife to livestock transmission resides with migratory elk that carry the disease. Photo courtesy Neal Herbert/NPS