Scientists and state officials have said that another wild animal, elk, are the biggest threat for the spread of brucellosis because they are more numerous and their movements are unrestricted.
Three conservation groups — Bear Creek Council, Greater Yellowstone Coalition and Natural Resources Defense Council — have intervened in the case on the side of the state. Their attorney, Tim Preso, said Monday that the ranchers and others opposed to bison in the basin do not speak for all of its residents.
"They don't represent the larger group of people in the Gardiner Basin that moved there to be closer to wildlife," he said. "If we can't conserve bison on the boundary of Yellowstone National Park, where we saved them from extinction, where can we do it?"
Most bison stayed inside Yellowstone last winter due to relatively mild conditions. Thousands have flooded out in other years.
The most recent count of the park's bison herd tallied 4,320 animals — enough to trigger a major migration this winter if conditions are right.