The bison herds of the North American grasslands once numbered in the millions before they were hunted by white settlers to the brink of extinction.
Now, almost miraculously, there are upwards of half a million again — but this amazing conservation success story isn’t music to everyone’s ears.
In the pre-colonial era, bison roamed from the Canadian north to well east of the Mississippi River in some of the greatest concentrations of animals the world has ever seen.
Since their restoration to both game ranches and the wild, there are 20,000 of the massive beasts living wild in U.S. parks and Indian reservations.
There is little controversy about their presence on fenced rangelands — but as more states move to reintroduce bison to unfenced areas, the potential for human-bison conflict increases.
In the greater Yellowstone ecosystem of Wyoming and neighboring states, where around 3,000 wild bison live, visitors are warned to steer clear of the huge and dangerous animals.
Yet every year, unfortunate tourists that get too close to Yellowstone bison are harmed and sometimes even killed.
Even vehicles aren’t safe — bison-car collisions are on the rise.
In addition to their destructiveness, wild bison are seen as a threat by many ranchers because they can carry brucellosis — a disease that can devastate commercial cattle.
Bison, as grazers, can end also up competing with cattle for the same grasslands.
The Eastern Shoshone tribe historically relied on bison for meat and hide, and the loss of the species was a devastating blow.
Now, the Shoshone are enthusiastic supporters of bison restoration on the multi-million-acre Wind River reservation that is their home.
In the Flint Hills of Kansas, the Tallgrass Prairie Preserve, run by the Nature Conservancy, is another conservation success story.
The organizaton bought Barnard Ranch in 1989 and reintroduced bison in 1993.
The herd there is still flourishing.
For ecologists and environmentalists, it’s more than just a story about the return of a keystone species.
The bison, it turns out, is an animal that maintains and restores the prairie.
Unlike cattle, bison are wallowers, so these powerful animals’ efforts to rid themselves of insect parasites, by rubbing their hide and rolling around on the ground, actually create permanent depressions, called bison wallows, in the landscape.
These create fertile ground for diverse plant species — and the animals that rely on them.
Bison also rub against woody plants and kill them off, keeping the prairies open, while their dung fertilizes the soil.
Iconic species like the greater prairie-chicken and the prairie dog all benefit from the restoration of bison.
Bison herds have also proved highly adaptive to the “new,” post-colonial ecology of the Great Plains.
They are adapting to hunting season, for example, by delaying their migration. This keeps them out of harm’s way — but also increases the risk of human-bison conflicts.
Ranchers, in particular, are frequent critics of bison restoration, which threatens their herds’ grazing lands, and thus ranching’s profitability and lifestyle.