It’s the time of year when the bison are exhibiting breeding activity (“rut”). While bison may be aggressive any time of the year, they are especially ill-tempered during the rut from mid-July through August, or when cows have calves. A cow with a calf can be even more dangerous than a bull.
At Wind Cave National Park there have been no documented cases of an injury caused by a bison, though one person did scrape their knee when they fell while running away from a charging bison. However, in Yellowstone National Park, more people are injured by bison each year than by bears.
Remember that bison are wild animals and should be treated with caution and respect. At Wind Cave, a female bison can weigh around 1300 lbs and a mature bull more than 2000 pounds. Bison are very agile, can turn on a dime, and run more than 30 mph (three times faster than people). They are unpredictable and may charge if surprised or if you enter their personal space (~25 yards). They are not easily frightened and are very curious about what’s going on around them.
If you encounter bison on the trail they will most likely get out of your way; however, there are some bulls that may stand their ground. Some may charge but these are generally “mock” charges and of short duration. As to what you should do if a bison charges…… there is no “perfect” answer. Your best bet is to back off and put as much distance as possible between you and the bison. You may need to climb a tree or fence, if one is available. The best recommendation is to stay 50-100 yards from all large wildlife to prevent a defensive reaction. Observing the position of the tail of a bison is a good indicator of what the animal is doing, and what it may do next. If an animal’s tail is up and head raised and alert, the bison most likely does not appreciate your presence. A relaxed tail, possibly in motion to flick away insects, indicates an undisturbed animal. A slightly raised tail indicates mild excitement. As the animal becomes more nervous the tail begins to arch. A tail raised to a vertical position signifies great agitation. Remember, a bison can also charge without warning. - Barb Muenchau