I hang the CDs, DVDs, also attatch shiny pinwheels to the posts and hang other cheap suncatchers that are sold at the dollar stores.
Make sure your chicks have a place to run & hide under in the center of their pen. Hawks can grab chicks through the wire sides of a pen if they're close enough to reach.
Hawks seem especially attracted to chicks, they prey on the weak, sick, and more helpless. It's nature's way to insure survival of the fittest.
I don't remember if you said you had a rooster or not. They're great for warning the flock about predators. They have a growly word that means "something flying overhead" and an especially bad word that means "hawk!" My roos have everyone trained, even me, to stop in our tracks and scan the sky when we hear that word.