Red tailed hawks, yes, they definitely will kill your adult chickens. Red SHOULDERED hawks, no. They prey on small mammals, snakes and frogs. From my experience, I've had more problems with eagles than hawks, contrary to what the majority of other threads have said. I have seen peregrine falcons fly over as well as red tails that didn't even look twice at my neighbors flock, but I have seen Cooper's hawks start to dive bomb chickens then retreat at the last minute when they realize the chickens are bigger than they are.