Grand Teton National Park is warning visitors the bison rut is in full swing in the park. Grand Teton has slightly more than 600 bison within the park boundaries. Although bison may appear docile, they are anything but that. Bison can run up to 35 mph and can be aggressive, especially during the rut season. Consequently, park officials urge visitors to be sure to give bison plenty of space – stay at least 25 yards away at all times. A bull stays very busy during the rut season, and can lose up to 200 pounds, or 12% of their weight; their attentions wander far from grazing during this time.