I let my 2 hens and 1 rooster free-range all day. I have seen hawks/big birds flying above. Ususally the girls stay close to the house, or hid under things. Sometimes my little rooster (white sultan) runs around out in the open almost teasing the hawks. I just came home to a trail of feathers (3 small patches - photos above) and no rooster to be seen. I'm assuming this was probably a hawk?
Time to get more chickens.