Eric -- You can free range quite a few birds on half an acre, but if you get up in the numbers it's best if you can rotate them around the property. We had (prior to locking them up for protection from predators) about 20 birds free ranging on 7 acres, but they pretty much stayed on two acres and it easily supported them with bugs and grazing. Very happy birds! On the other hand, when we concentrated 35 young NH Reds on a quarter acre, they ate everything right down to the roots! /forums/images/graemlins/shocked.gif That section of land is like a desert now. It was the first time we did not confine the youngsters to portable chicken tractors to enforce the rotational grazing thing. Won't make that mistake again!
Not sure what your predator situation is, but we have foxes, fisher cats and the occasional hawk to deal with. Our worst predation by far is domestic dogs off leash, but the furious shotgun blazing wife scared the worst offender so badly he hasn't come back in months. The sad thing is she's such a bad shot when she gets excited the only thing she managed to hit was my backhoe! /forums/images/graemlins/shocked.gif That's why I only give her #8 shot. /forums/images/graemlins/wink.gif
Best of luck.