My chickens were bought as chicks so they had to learn about predators first hand. I lost several to hawks but I noticed when they were free ranging they would run across open ground to get under cover. They had to have learned that from experience. I pen them up every night, but occasionally because of weather, etc.. To keep hawks from swooping down on them, while they are penned up, I stretched fishing line across the top of the fence every few inches. This has worked great for me. It seems like, when I bring in new chicks, the old rooster teaches them to be watchful as well as the hens. I lose a young one every once in a while but I think that re-enforces the flock to be more observant. My worst predator is coyotes. I lost my whole flock several years ago; I'm still sad about that.