The hawks are out in Central Texas, beware. I am newer to free-ranging and we've had our chickens out almost everyday since spring. We have trees but also a lot of field. The other week a hawk had our best chicken held to the ground, but luckily our neighbor was there and scared it off in time! Thank God, somehow she survived only missing feathers no blood. One of my neighbors a few houses down just had one of their chickens taken by a hawk a week ago. We got very lucky.
I am so paranoid now, I am not letting my chickens out of their run except for key times when I am outside with them. I'm building them a larger aviary now. The hawks are way more active right now in fall than I've seen previously and there are 2 brother red tailed hawks that I keep seeing around 2:30 in the afternoon.
I don't trust the fake owls and plus you have to move them around constantly, but it is better than nothing. Not sure about the owl screech.