15 Facts About Bison. On May 9, 2016, President Obama signed the National Bison Legacy Act into law, officially making the American bison the national mammal of the United States. This majestic animal joins the ranks of the bald eagle as the official symbol of our country—and much like the eagle, it's one of the greatest conservation success stories of all time. 15 Facts About Bison (U.S. National Park Service) 5. What's a 'red dog'? It's a baby bison. Bison calves tend to be born from late March through May and are orange-red in color, earning them the nickname 'red dogs.' After a few months, their hair starts to change to dark brown and their characteristic shoulder hump and horns begin to grow. Last updated: November 16, 2016. 15. Bison are nearsighted—who knew? While bison have poor eyesight, they have excellent senses of smell and hearing. Cows and calves communicate using pig-like grunts, and during mating season, bulls can be heard bellowing across long distances.