I drove out to Poland years ago to see the remaining European bison there. I was directed to them really quickly by a forester and watched a family group slowly coming towards me in open woodland. Slightly unsure of how they would react to me, when they were about 50yds off I got 10ft up a tree. They were totally uninterested and fed past me on either side of the tree. They took so little interest I'm still not sure if they actually knew I was there! Probably wouldn't want to get one annoyed though....