The bison of Lamar Valley

There's a rule in Yellowstone: keep at least 25 meters from bison. There's also a reality: bison can't read and don't follow rules.

We were standing at Lamar Valley early one morning when the herd decided to wander right across the road where we'd parked. Suddenly the distance was no longer a matter of regulation, but one the animal decided.

Alexandra shot through the half-open window, David filmed with shaking hands. What remains is not just the image — but the feeling of having been, for a moment, a guest in a world that doesn't need us.