Genetics is certainly something to think about. I have other breeds on my wishlist but they are just not available or there isn't much genetic diversity. I had a lot of issues with Amrock in terms of genetic problems so decided to give up on them.

Luckily our current Jersey flock has produced many succesful generations but only the oldest hens great-grandfather had "true" American blood so to speak. The other lines were bred here in Europe.

As far as predators go we have many birds of prey. The chickens must have the instinct to run for cover, if they don't then they won't have a place here. Harsh but it's as simple as that. I make no exception for bantams but they usually hang out near our pile of logs so they have their regular hiding spot. Some of the Hampshires had zero notion of danger and I'm surprised non of them got eaten. They went on to a new home.
Other predators involve mostly rats and foxes but they are sensitive to me moving the chickens around daily. I need to be watchfull when chickens are near tall grass or when I have young chicks. I lost chicks to rats once when I DIDN'T move them, never ever will I forget. Moving is the key.