I've got a laying flock of 80, free range and locked in a coop at noght, 7 tractors with 35 meat birds each, rotated as they reach slaughter age, and 15 dairy goats. The area where I live has numerous roaming dogs, coyotes, black bears, possums, and raccoons, not to mention hawks and owls...and I have lost ONE chicken in four years, to a hawk yesterday. I watched it happen, and while I hated to lose a chicken, I must admit it was kinda cool seeing nature, survival of the fittest, actually happen.
With that said, I attribute the lack of losses to good fencing for the goats, a well constructed coop and tractors for the chockens, and a very protective Anatolian Shepherd that loves her livestock and is hell on anything that threatens them.
Bob