I used CDs to deter a red-tailed hawk from nest robbing.
We had a little robin couple build a nest behind one of our lanterns near our garage, up against the wall. When the babies were about 4-5 days old, I was talking to my mother on the phone when I saw an enormous red-tailed hawk swoop in sideways, ready to raid the nest. I'm used to running them off of my birdfeeders, so I jumped up and slammed the glass windows with my hands, and the hawk veered off and left. I was desperate to keep this hawk from raiding the nest--I know it probably had babies of its own to feed, too, but I wanted it to go find some that I didn't have to watch die--so I hung four CDs from twine about 12" from my gutter. Worked like a charm. Mama Robin wasn't deterred by them at all, but the hawk never returned, and nobody else got any bright ideas, either. Three of the four babies fledged.
Amy