I have 10 hens that roam outside in a 1/8 acre area surrounded by 6' fences. It is surrounded by neighbors yards, so not technically "out in the open". I live in a rural neighborhood, so not may predators besides the occasional stray dog that couldn't get in anyways. I do have 1 or 2 girls that have jumped the fence, then they go crazy trying to get back in
But I haven't had any problems. I think it really depends on what type of predators you have in your area and how easily they can access your girls.
