Battle of the Bison or Clash of the Titans? You've got to fight for your right to breed.
During the rut, or mating season, bulls display their dominance to find a suitable mate. And these bulls do just that by butting their heads together and pummeling the bejesus out of each other before one trots off as champion. In fact, the males have a thick mat of fur on their forehead during the summer, which acts as padding during these annual bouts of headbutting. To that end, they also have special “bone struts” in their skull to prevent brain damage. (We have more bison fun facts here.)