Now the bison number well over 20,000. Being primarily grazing bovids, Bison live in herds that vary from a family group to several thousand. They then migrate in search of better pastures. In the winter, Bison thrive and being a hearty breed, their coats thicken and are prized. Mating season begins in the fall and continues through January - this is the only time bulls fight for cows, which give birth to a single calf, away from the herd.
Calves are generally able to join the herd within an hour or two after birth.
Both the bulls and the cows have horns. When defending against danger, the cows will form a defensive circle around the calves, and the bulls will form a circle around the cows. While this worked well against wolves, it was a poor defense against humans who shot them for their hides and tongues or for sport. There were once three different species of Bison in the USA, numbering an estimated 50 million. By 1906, there were only about 800 Plains Bison left, now there are over 50,000.