As I later realized, one bird was hitchhiking through an others territory on the back of one of these lumbering beasts. The territory holder was repeatedly swooping and calling at the other. Of course the bison were totally unaware of this drama unfolding around them.
As for the title... I reference the scientific name of this fascinating bird. I love the fact that it's thought that birds are descendants of dinosaurs and that this bird in particular is named Tyrannous tyrannous. The 'lizard king' as it's referred to seemed an appropriate choice to name this aggressive and territorial little flycatcher. I simply could not resist the grand title to honor this wonderful bird. The bison are just there as supporting actors.