The plains bison is the largest land mammal in North America with some adult bulls weighing in excess of 2,000 pounds. Tens of millions of these iconic animals once roamed across much of North America. Today, the largest remaining wild herd of approximately 4,500 individuals can be found in Yellowstone National Park. Large North American grazers including the plains bison traditionally roamed across millions of acres, which kept the grasslands and herds healthy and diverse. However, early settlement and current land use by present-day communities have redefined where these large animals are able to roam. WWF’s Northern Great Plains Program is working with National Parks, native tribal communities, and its ranching partners to find common ground on returning bison to suitable intact prairie landscapes.

An overall population of just over 20,000 plains bison managed as wildlife in North America and small herd size among them contributes to the ongoing loss of genetic diversity. Therefore long-term conservation of existing diversity is at risk. Early 20th century experiments to interbreed bison and cattle with the goal of producing heartier livestock has also had an impact on population viability. At present, there are only believed to be two public bison herds that have not shown evidence of interbreeding with cattle to date; Yellowstone NP, and Elk Island National Park in Canada. Conservation groups have been working hard to establish additional herds elsewhere to safeguard these valuable genetics should a catastrophic event (e.g. disease outbreak) threaten these source herds.