This article from the WSJ says that chickens fear of open spaces, typically attributed to cowardice, maybe just good common sense, in a study done at the University of Wurtzberg, Germany demonstrates. The idea is that open fields are evolutionary anxiety triggers, as larger predators can move faster over it than their smaller pray, whom in turn have no place to hide. I have seen this in action in my own fields, when a chook is cornered by the big hulking Russian wolfhound, aka Borzoi. Gusto can literally tear up ground in seconds, while the little chook is frantically trying to make flight. If not stopped in time, it's dead meat as Gusto loves the chase but not the raw bird.
From Food & Wine, a green chicken dish.