Do you know what kind of predator took your hen? We found with our open range hens that hawks won't go after them because we have a lot of low shelters, benches, yard equipt, plants, doghouses, and popup canopies as hiding places. We also have a couple thorny rose bushes that hens seem to like to snooze under - guess the thorny plants give them a sense of security and we noticed the hawks won't tread into the bushes. The Cooper's Hawk has been as close as 5 feet from our hiding girls but for some reason doesn't go after them when they're hiding. I guess aerial predators like open range to swoop down on easy prey and don't go after hiding hens. Your field looks pretty open and sparse for any shelters. Provide a few large doghouses, low-to-the ground plywood sheets mounted on a couple cinderblocks or similar and have them scattered about the field. It really helps to give the hens a chance to hide from the aerial attacks and will save the roos from having to sacrifice themselves to hawk attacks. Since we've scattered these shelters around the yard we breathe easier knowing the girls are savvy enough to dive into a doghouse, under a rose bush, or under a plywood shelter if there's a barnyard alert. It's good to have several shelters so the hens don't have to run far to hide. A running hen is an invitation to a hawk.