Prior to 1800, it was estimated that nearly 30-60 million Bison roamed the North American continent from Alaska and northwestern Canada to the Great Plains and Gulf Coast of the United States. and northern Mexico. Through excessive hunting during the 1870’s, the species almost became extinct and in the early 1900’s it was estimated that fewer than 1000 North American Bison (Bison bison) survived. In fact, fewer than 500 individuals served as foundation stock for the buffalo herds we see today. Of the estimated 500,000 bison found in North America, only 5 % are set aside in conservation herds. Over 95% of the Bisons today are to be found in private and commercial herds. 2 of the largest Conservation herds can be found in the Greater Yellowstone area, and Wood Buffalo National Park in Alberta, Canada.
Through conservation efforts the species has rebounded after going through a severe genetic bottleneck that could have threatened genetic diversity. In the early days of conservation Bison were bred with cows to increase herd size, and commercial value through hybridization with cattle. Genetic studies & testing indicates that a high percentage of buffalo even in the conservation herds have cattle genes, and are not considered to be pure with exception of the Yellowstone National Park and Wind Cave herds. (Halbert, et all 2007, and Gates, et all 2010.)
Additionally genetic testing of various herds appears to indicate that despite genetic inbreeding, the relative genetic fitness of the American Bison is quite good, and did not show significant amplification of harmful genetic traits (with exception of the Texas State Bison Herd which has a relatively low viability rate due to sperm abnormalities, and high mortality rates in calves) possibly due to inbreeding and a decrease in genetic diversity. Inbreeding was shown to reduce fertility, lifespan, and even the survivability of juveniles (Frankham & Ralls, 1998). Despite all this, the comeback of the American Bison from near extinction has been one of the great success stories of conservation.