Be mindful it is unlawful to shoot red tail hawks, and I believe vultures are protected as well. Vultures only go after dead animals so I would not think they would bother live chickens.
In the beginning I saw and heard only red tail 2 hawks, but they must have went and told their buddies. One day I looked up and there were 8 circling high over my chicken pen. I tried hanging CDs and it seemed to work for a while. They had killed my black sex hen and eat a few bites and left...