As discussed previously, I keep my chickens in tractors. It works well to give them additional food for their diet, thus saving on feed costs, and in theory it helps fertilize the grass. After some early predator issues, I set up some electrified netting and have had no further problems.
They spend most of the day in the tractors. They're also out some of the time, but they don't free-range. I often see hawks on top of the muscadine trellis posts, and I'd have serious predation issues if I let them out for the whole day. The tractor moves back and forth until it covers most of the area inside the paddock, then they get moved. As can be seen (both above and below), they do scratch down to bare dirt sometimes. The area needs time to recover after they have been there (recovery can't happen in a drought or in the dormant season; in those cases, the tractor gets parked and hay is used inside the tractor to provide bedding and what Joel Salatin calls a 'carbon diaper').
The aftermath of the chickens' work in the foreground paddock can be seen here:
These pictures were from spring; they subsequently moved to the right, but now (a couple of months later) they are back in the center area again. The other chickens move between two areas, as well. Given enough rainfall, the system works well.
This ground-level shot shows that the grass is a little darker green in the area where the tractor was, and it also shows a few more torn-up spots than were present before the tractor moved through. That's a pretty fair assessment of how it goes.
