Owl decoys work until the predator bird realizes that it does not move. Then one day you look out your window and see the hawk siting on top of the owl decoy. The great thing about old CD's or reflective tape/ribbon is that it moves with the wind. They don't work 100% of the time but they do work. Owl decoys will work if you move them every day or two.To keep birds of prey away I use old CDs tied to strings across the yard (found that info here 2 years ago on some thread...it works). The reflections keep them away. However, my Grandpa used owl decoys...... just as someone above has suggested.