These two bison were positively posing for us. The bull would trot away toward another male threateningly to show off his power and dominance, then return to this cow. They were inseparable. We think we saw the same pair next morning, always just a bit away from the rest of the herd, always close to the point of leaning on one another even when grazing. I know far too little about bison behaviour to make anything of it, but it sure looked sweet.
More photos from the same session: