I was reading about hawks on this site recently as I have enough of them to be worried. When I first got chickens (little, light silkies), I'd let them free range in the yard. One day I heard my rooster making a really odd noise and when I went to see what it was all about they were all huddled next to the house with a hawk diving at them. That was it. I covered the run with netting and only let them free range when I was with them.
Recently, I got some new silkies, no rooster, he died of old age, and they live to free range, but after reading some of the stories on here, I'm really uncomfortable when they are out of their run, even if I am very near by. People have posted how hawks grabbed a chicken not five feet from them!! Kind of wrecked hanging out in the yard with the fluffs for me. Now I get a stiff neck checking the skies for large, slow flying birds. I bought some crow decoys...haven't used them yet, but some say they deter the hawks because crows will bother them. I have no idea if they really work.