I have some hens at my mom's house. This morning I was up there with my step father. We were sitting there watching the birds and chatting when all of a sudden the hens froze, cocked their heads a bit and started humming. We figured they saw something but we couldn't see anything near us. The sound they made was weird but I'm new to chickens so that made it even weirder. Not sure calling it a hum is the right word. Y'all know what I'm talking about? Anyway, the dog barked and we saw a hawk fly off behind us. The hawk was about 100-125 yards away up in a tree so I guess that's what the hens saw. Once the hawk flew away they stopped that humming. It was a pretty neat thing to see. p.s. The run is covered with wire so no fear of the hawk getting to the birds.