We've been free ranging for >2 years. The chu all put themselves to bed just before dark, and the only one we've lost to a predator besides the odd chick from an inexperienced hen is our alpha roo that was compromised due to illness. But it didn't start that way.
Our first brood was ravaged in one day by what almost seemed to be syncronized fox/hawk attacks after successfully foraging in the woods for months (forest floor was clean… poison ivy gone, ground was plucked and black, it was amazing.) The ones who survived (a couple were ptsd for awhile) remembered what happens in the woods. We still have 2 of them left and they don't go there. There are all kinds of predators here, ranging from the indigent panther to an odd skunk, but the larger ones usually won't come close to the house. We lost several to hawks until our mockingbirds put them on the run; haven't had a hawk attack in over a year, but snakes get chicks occasionally (since my hens all like to go broody now… if I hatch chicks I keep them enclosed until they are at least a cpl months old or more, but my hens… naw. I've had young roos lead hens into the underbrush and lose them occasionally as well. But generally roosters, especially my one alpha that survived the original attack and never strayed far afterward kept all his girls close to home. He saved more than one hen, and of course roos are generally better at paying attention and sounding alarms, so I highly recommend having a good roo present if you are free ranging. We also have a dog that keeps many small predators scarce, but she's getting old and doesn't hear as well as she used to.
One risk is poisonous plants. I've come to the conclusion that chickens instinctively know not to eat the azaleas and English ivy, and they go hard after certain types of edibles, particularly wood sorrel and plantain. My son had a terribly handsome rooster named Heather (who was sold as a pullet) who was none too bright and just checked out one day and died over the night. I was unaware, but my husband had noted he didn't even flinch when the car passed him and he was just walking aimlessly and staring into space. I guessed it was either a bad mushroom or snakebite, but that's the only incident I know of.
Another is rain. Usually they all know exactly how to get back to shelter, but one hen derped with 10 3-wk-old chicks and by the time I found them, 3 had collapsed to the ground and all were soaked; I got them under the heat lamp and revived them just in time. Perhaps there is a thread on micromanaging broody hens that can't protect their young.
In that hen's defense, it was her first brood. She abandoned them early, but a small rooster with no standing in the community had been trying to win her affection and ended up with that of the chicks instead. He became their surrogate and since he was small and prone to be abused by every other chicken in the yard (even the hens except the 2 youngest,) he had learned how to make himself virtually invisible. He led the whole brood into the forest and trained them well, for only one was lost to this day, and she was a terminal straggler. Unfortunately, he was murdered in the coop by his own people, we were never sure exactly who was the guilty party, for there were no witnesses come forward and the suspects never confessed.
Other than that; adult male human urine is often a deterrent of mammal predators, free range birds may think they own the house and poop everywhere you don't want them to or dig up the yard dust bathing. We are far enough from the road that crossing to the other side has never been an issue. My birds seem healthier and happier for being able to range on the whole.
