I think chicks in a brooder are use to being handled and think not every big thing is going to eat them. So they don't fear everything like my broody raised that the mother keeps them away. The broodies that come up to me with the chicks have the most attacked chicks. Usually just after she abondons them and they are on their own during the day... They are wandering around in the open. So far I have intervene on all attacks and not lost any to predators. I hear the roosters or turkey alerts and run out. Usually a young hawk. Amazing how well they heal.Thats an interesting observation. I wonder if the incubator and human reared chicks are generally more fearful.
It also makes one wonder if predator awareness is learned, or is genetic, or some combination.