Some chickens can die from a stress induced heart attack. They will show zero signs of puncture wounds or any surficial injuries. That's what happened to a few of my Cornish crosses when a fox slipped under the electric poultry fence (which had been temporarily turned off!!)
If you want the best tasting chicken, raise the Cornish cross on an all organic diet and free range diet. If you want tough, stringy, shoe leather chicken, then raise any other chicken and try eating it.
4-5lbs for a 12 week Cornish cross is pretty small. Mine were 10-11 weeks old and foraged/free ranged within their poultry fence and weighed in at 6-9lbs. I fed them once a day.
Bears are repeat offenders. We had a bear this summer that was only interested in our garbage bin. He would walk right past a group of 90 Cornish cross, huddled outside (protected by a electric poultry fence) and proceed to tip over the garbage bin, grab a bag and run towards the bush. He had 0...
What are your daytime and nighttime temperatures and how old will they be when you get them? Most likely you will need heat lamps. 0-7 days old require 95F, stepping down 5 degrees every week until 4 weeks old.