I also free range, lose a couple every year. There is no practical way to secure acres.Above you got advice about risk tolerance. We used to let out girls range in a 20’ x 50’ fenced area. Over 4 years we have lost have a dozen pullets and hens to predators. Hawks, maybe fox. And yesterday this guy got caught in our home made bird netting. I managed to free him and he flew away. We are in the suburbs of Boston.
My hatchlings get their own pen and run outside at around 3 weeks, and join the main flock free ranging between 8-9 weeks.
I've lost more birds to crushing injuries and the like (I also have ducks, and goats, in the same pasture) than I have to predation - but it does occasionally occur.
Note, ducks - particularly male ducks - and chickens should NOT occupy the same space. Yes, I do it, but I have a pretty unique situation. For most people, duplicating my experience and conditions is impractical and/or unrealistic. I'm not sure where, exactly, the line is drawn between acceptable and not - but if you have the choice, DO NOT DO IT.