I've been researching how to deter hawks and owls from our free-ranging chickens. The CD's sometimes work, but they aren't very aethestically pleasing. One thing I discovered was using mirrors. I'm purchasing those long "door" mirrors from Walmart for $5.00 each. You place them in strategic places around your coops/yard/runs with the mirrors at a slight angle upward toward the sky. Apparently they work 2 ways. First, the hawks see themselves in the mirror and think it is another predator. Second, the light glancing off the mirror confuses them and keeps them from being able to see well. It's probably much like using the CD's as far as the light glancing off. We'll see how well they work and I'll let you know.