Ours roam a fenced space about that size. Lots of trees and shrubs. In fact, until we fenced it for the chickens it was difficult to walk through it, but they've eaten or trampled a lot of the small stuff. Sometimes I see them standing very still under shrubs while a hawk sits in a tree, but we've lost none to hawks. The "flight path" for a hawk would be challenging.
For a few years before that, they were truly free-range and some of their space was more open but no losses then, either. It's a pretty wary bunch of birds and they are watched over by a very capable rooster.
I've heard that stringing monofilament fishing line above them will keep the hawks away and I think it probably would, if you had enough of it. I decided not to try it when I realized what it would take to get it up high enough and spread out far enough.
Any cover would need to be close by when they need it. A diving hawk moves very fast.