Although their numbers shrank to a perilously small figure at the end of the 19th century due to overhunting, bison weren't federally classified as an endangered species in the United States. Instead, private and public conservation efforts gradually nudged their population upward, with the greatest increase occurring in the last 40 years.
Nevertheless, the U.S. wild bison population today is less than one percent of what it was in pre-colonial times, hovering at around 20,000 animals.
A handful of factors have inhibited more robust bison population growth. Perhaps most influential is the sheer lack of space. Bison are prairie grazers, and much of their native land has been developed. Because the existing bison herds have remained relatively small, that has also diminished the diversity of the bison gene pool. Once that happens, inbreeding can increase the rate of health problems in a herd.
DON'T MIX UP THIS WITH THE BREEDING BISON WHICH IS MENT TO BE KILLED AS FOOD
