Heat enough oil to coat the bottom of a large, heavy pot. Add the onion and sauté over medium heat until the onion begins to soften, about 5 minutes. Stir in celery, bell pepper, and garlic and cook for 1 minute.

Push the vegetables to the outside edge of the pot and place the ground bison in the middle. Break up the meat and cook for several minutes, occasionally flipping the meat over to brown the other side, until the meat is no longer pink.

Stir the vegetables into the meat, adding extra oil if the bison is beginning to stick to the bottom of the pot. Add the chili powder, paprika, and cumin, and cook for 2 or 3 minutes, stirring occasionally. Add the chopped tomatoes with their juice, the cooked beans and the bean liquid, and, if necessary, extra water to keep the beans from sticking to the bottom of the pan. (Add as much water as you like, depending on how thick or soupy you like your chili).

Bring to a boil, then reduce heat to a simmer. Cook, partially covered, for 1 hour. Stir occasionally and add more water if the chili begins to stick. Stir in the chipotles and season to taste with salt. Serve hot, with sour cream, grated Cheddar cheese, chopped white onions, and tortilla chips, if desired.