Very few types of hawk will take full size chickens. It takes a very big hawk to even try it.
However, if you have hawks that do eat chickens, your only truly safe way to keep poultry is under cover. Perhaps allow them out while you can stand right over the top of them to protect them.
I seen a group of hawks around 5-7 of them in the air gliding around my chickens and making load sounds, don't think they were red tail hawks, but the smaller cooper hawks.. Cooper hawks wont bother adult chickens but a red tail hawk might..