After many years of keeping chickens and having hundreds of them, I have only lost about 5 to a predator. Those five were in one incidence and NOT while they were free ranging. They were locked in their coop and my own dog chewed through her steel cable and got into the coop, while I wasn't at home.
At that time I lived in town, in an unincorporated area with 12 acres of pasture to free range in, and they were out dawn to dusk every day. I had 50+/- chickens.
When I moved out of town, I had a little over an acre that was completely fenced in chain link to free range. No losses, and about 25 chickens then who were out dawn to dusk every day. There was a huge owl living in the tree that shaded their coop, and it never bothered the chickens.
I have had more chickens in other locations that free ranged from dawn to dusk every day with no losses.
Now, I have 10 acres and can't free range at all because of the loose dogs in the area, just not safe and I'm not willing to lose any of my chickens. I've been getting more fencing from Freecycle, so hopefully I will be able to at least expand their run which is now about 15' x 30'.