Bison Begin to Return to Their Old Home on the Great Plains

by Richard Conniff/Smithsonian Magazine

Sometime this winter, if all goes as planned, a caravan of livestock trucks will carry 60 American bison out of Yellowstone National Park on a 500-mile journey into the past. Unlike their ranched cousins, which are mainly the result of nineteenth-century attempts to cross bison with cattle, the Yellowstone animals are wild and genetically pure, descendants of the original herds that once astonished visitors to the Great Plains and made the bison the symbol of American abundance. Until, that is, unsustainable hunting made it a symbol of mindless ecological destruction.

When the appalling mass slaughter of 30 million or so bison finally ended early in the 20th century, just 23 wild bison remained in Yellowstone, holed up in Pelican Valley. Together with a roughly equal number of animals saved by ranchers, they became the basis for the recovery of the species, Bison bison, carefully nurtured back to strength within Yellowstone National Park.

Yellowstone has done its job so well, in fact, that the herd now routinely exceeds the limit of about 4000 bison thought to be sustainable within park boundaries. Park rangers have thus had the disheartening annual job of rounding up “excess” bison for slaughter or watching some step across the park’s northern border into a hunt that critics deride as a firing squad. Relocating the animals would be the humane alternative, except for one scary problem: Ranchers and others have long maintained that bison spread brucellosis, a bacterial infection that is devastating to both cattle and bison. But an authoritative 2017 study using whole genome sequencing determined that