twice a year, the birds fly full speed into them. I guess it's because of how the sky reflects when the sun is at a certain angle. I tried hanging owl cutouts and tin foil strands to scare them. Didn't work. Then, I remembered the rubber snakes the boys had that were still in their closets. They were 5 feet long, very realistic and I draped them over the railing by the front door. No more bird strikes, but two days later, the UPS guy knocked on the door and screamed at me, "Lady, that isn't funny!"