Once upon a time, there might have been 60 million bison on the North American continent. The herds were so large that they covered prairies like immense horizon-stretching black cloaks, and their annual migrations carved such wide paths into the landscape that some were turned into roads by human travelers.  As vast as bison herds were, the species came extremely close to extinction. By the end of the 19th century, there might have been two dozen bison left in the wilds, and they were deep in the heart of Yellowstone National Park. Today however, there might be 500,000 bison in North America, though most are in commercial herds meant for meat production. Designated the national mammal back in 2016, bison are truly charismatic megafauna. So charismatic, in fact, that Dayton Duncan and Ken Burns, who profiled America’s National Parks back in 2016, are soon to release a documentary on the history of the bison.