If you can reduce their spots to perch, it may help reduce the loss. If they are sitting on fence posts, drill a hole into the top of the post and stand a piece of heavy stiff wire upright in it. This denies them the perch and forces them to perch further away and gives your chickens a little longer to react to the attack. If the hawk is sitting on a roof ridge or fence rail, a single strand of wire stretched tightly a couple inches above the perch will deny them that perch too. (you never see a hawk sit on fence wire, it's too thin to hold on)
A good alert protective rooster will growl a warning to the hens (and all your fowl will react), will attack the hawk to protect his exposed girls and will fight to the death too. Give the birds several hide spots in their area, a elevated pallet or brush pile is great for cover plus provides shade. If the hens need persuasion to use the spots, put a water source under it, they will find it.
This is some of the technigues I have had success with in fighting eagle and hawk issues. Not very effective against ravens
