As hundreds of bison make their annual winter migration out of Yellowstone National Park, most are hazed back into the park. Others are captured, quarantined, and occasionally slaughtered.
This year, more than 500 bison are being held by state and federal officials. If the bison test positive for brucellosis, a disease that can spread to livestock, they risk being killed.
However, new federal brucellosis regulations have the potential to change the hostile attitudes towards bison by state agencies and ranchers, who have long fought to keep bison inside Yellowstone and away from livestock rangelands. The new rules, released in December and open for public comment, may also lower the costs of bargaining between bison advocates, who want an expansion of bison wintering habitat, and nearby livestock owners.
First, some background information. Bison once numbered in the tens of millions across North America. By the time Yellowstone was created in 1872, there were less than two dozen wild bison remaining. Aggressive park management resulted in rapid bison population growth throughout the first half of the twentieth century. So much growth occurred that culling the herd became necessary to maintain the population within the estimated carrying capacity of the park.
Opposition to the culling, however, brought changes to the park’s bison management policy. In 1968, an ecological management approach was introduced, leaving wildlife populations to self-regulate according to ecological conditions.
But Yellowstone is not a self-contained ecosystem for bison. As bison numbers increased, their required acreage increases as well—meaning that bison began to roam beyond the park’s borders. Without population control, Yellowstone’s bison numbers grew even more rapidly than before, from 556 in 1968 to as many as 5,015 in 2005.Today, bison numbers remain high. The most recent survey counted 3,900. More bison means more land-use conflict as animals routinely cross the northern border into Montana in search of wintering habitat. There, the bison compete with livestock for forage and risk causing the state to lose its brucellosis-free status.