We've been doing this since 2008 and have only lost 4 birds to any sort of predator. One the wind blew the ropes open wider, 1 was a weasel (not much stops them), 1 was a juvenile Cooper's hawk that fit between the ropes, and 1 was a hen that got out of the pen and was picked off. So the system works real well here where our predator load is sky high.