Walked past the back door and all the chickens were on the porch, totally frozen. Walked back and forth several times, looked out the windows, but they never flinched. Some were totally flattened on the concrete. Even the rooster was hunkered down. I opened the door to go out and none of them moved; I had to step over the flattest one. Well after I got a few steps out the rooster started pacing and calling loudly, but no one followed me off the porch. I looked all over the yard and in the trees and never saw anything. I went back in and they all hunkered back down. Maybe there was something on the other side of the fence? Whatever it was spooked them good.