We just moved to our new property earlier this year and this is my first time dealing with birds of prey... suffice it to say that I underestimated them. On my neighbor's advice, I didn't even try free-ranging during midday due to the hawk presence in the area. The chickens get to run around from 5pm until sundown. Other than that, they have 24/7 access to their covered runs.
Welp... a couple weeks ago a great horned owl literally squeezed himself into one of the coops through a 4"x5" gap and took out 6 pullets. Apparently none of the cockerels took it upon themselves to intervene, as they're off the clock as soon as they hit the roost.

After he dispatched the girls he couldn't find his way back out. I did my best to scare him silly and then let him go. Well, wouldn't you know it — he came back that very same night after I went to bed, squeezed his way in again, and finished his meal (just the ones he'd already killed, thank goodness). He was in the coop, fat and happy as a clam, when I came in the morning to clean up the bodies.
My takeaway: birds of prey aren't scared of you and don't care about whatever obstacles you throw up at them. If they're around, chickens either need to be very well secured or need to be able to get somewhere the larger birds can't access.