American bison during snowfall, in Yellowstone National Park, Wyoming. European colonials slaughtered an estimated 50 million bison during the 19th century, reducing their population to hundreds and close to extinction. Extensive ranching began in 1910 and have continued (with excellent success) to the present day, increasing the bison's population to nearly 150,000, and it is officially no longer considered an endangered species. However, from a genetic standpoint, these ranch animals are actually hybrids with domestic cattle and only two populations, in Yellowstone National Park in the United States and Elk Island National Park in Canada, remain as genetically pure bison. These genetically pure animals account for less than 5% of the currently extant American bison population, reflecting the loss of most of the species' genetic diversity.