What happens in the future?

In order to avoid a time paradox, they are very careful to leave history undisturbed on the principle that even the slightest change can cause major changes in the future. Travelers are only allowed to shoot animals that are already about to die, and they are required to stay on a path which hovers slightly above the ground. Hunting trophies are not taken; no souvenir is allowed except a photograph of the hunter standing next to the dead monster.