I found some human tracks near my home, the remains of a fire, some lynx bones, and a lot of arrows laying around. I eventually caught up with the adventurer who had been hunting there. I think he should try to collect some of his arrows after he is done hunting -- he shouldn't succeed at finding all of them but if he happens to be within a few tiles of his arrow he should pick it up.
I noticed the arrows didn't have ownership on them though when I picked them up, so I guess it'd be tricky to work out which arrows he should feel free to take and which he should leave. If I leave arrows around my settlement then they are mine but if I shot an arrow farther away from my settlement and don't collect it then it would be fair if some adventurer took it.