Crows are interesting birds. They nest across the road from us and are harrassed by eagles more than hawks. Since I've moved the hens and chicks down to the field across from the crows, I see the crows hanging around more. They have never acted aggressively toward the chickens but are always there chasing the eagles away. I know the eagles raid the crows nests and assume this is the worst time because of babies hatching. If your girls are out, make sure they have plenty of cover where they can run and hide. Trees with low branches and shrubs are good places to take cover. Good luck.