Like indicated before, provide some kind of cover that the chickens can get under when the "hawk alert" goes out. Dog houses or crates, cattle panel bent to make a U with a tarp over it, plant bushes, something the birds can get under. Another thing you might try is attracting crows to the area. Put up some tall bird feeder platforms and put corn on it. Crows will run off hawks that come into "their" area. That said, crows have been known to take an occaisional chick or egg, but if they are being fed, they may not bother the chicks. Good luck!