What Bison heard is a herd of 250–400 American bison in Wind Cave National Park, South Dakota, USA, that  is one of two subspecies/ecotypes of the American bison?
Wind Cave bison herd The Wind Cave bison herd is a herd of 250–400 American bison in Wind Cave National Park, South Dakota, USA. It is believed to be one of only four free roaming and genetically pure herds on public lands in North America. The other three herds are the Yellowstone Park bison herd, the Henry Mountains bison herd in Central Utah, and at Elk Island National Park in Alberta, Canada. The Wind Cave herd are of the Plains bison subspecies ("Bison bison bison").
Sierra Nevada bighorn sheep Sierra Nevada bighorn sheep ("Ovis canadensis sierrae") is subspecies of bighorn sheep unique to the Sierra Nevada mountains of California. A 2016 genetics study confirmed significant divergence between the three subspecies of North America's bighorn sheep: Sierra Nevada bighorn sheep, Rocky Mountain bighorn sheep and desert bighorn sheep. Sierra Nevada bighorn sheep were listed as a federally endangered subspecies in 2000. Today, about 500 Sierra bighorn remain in the wild.