Hi Corky,
This is no simple question: too many variables!! However, lets look at some of the parameters.
1. I've been told "organic" standards say 4 sq ft/bird. This may work in huge barns with 100+ birds, but I don't agree that if is at all suitable for small flocks. I've read that
chickens can recognize up to 60 other "chickens", but tend to form strong pecking orders up to maybe 30 - please don't quote me on this, as I don't have the references to check on it right now. The important point is not the exact number, but rather that fact that at 4 sq ft/bird, the bottom bird in the pecking order has no place to hide and if anything disturbs the established pecking order, bad things can happen very quickly. Once you have a bully habit established, it can be difficult to impossible to cure, so prevention is essential.
2. Gail Damerow (see her Story's Guide or other
books) recommends 8 sq ft /bird and I consider this much more realistic as a starting point. For close confinement of a small flock, I still think it's on the low side.
3. Daytime vs full-time density: If you're intending to have a secure night lock-up and daytime runs, you can have higher density for night-time. However, consider whether there will be *any* occasions when the shit hits the fan before you use that as your only guide. Some people have a secure lock-up with an almost as secure run that can be the back-up system when letting them out into less secure paddocks can't happen. A deep mulch system in this paddock is likely the only way to go, but putting down sections of 2x4 frames covered in hardware cloth and growing fast-growing greens like wheat or oats is great for the entertainment value. When the greens are exhausted from being mowed, move the frame to a new spot and re-seed and let the birds dig up any bugs that collected over the old spot
4. Entertainment value: The more stimulating/entertaining their environment is, the less space you have to have. But, to keep the environment entertaining, you need a low density or the chickens will just destroy it, so it's a catch 22. Some people put chicken plants in old tires to protect the
roots in paddocks +/- using the screen idea to increase the food and soil protection if there's an area getting too much attention.
5. Mulch - chipped and shredded tree or dead leaves - help any system you use. Chickens produce a *lot* of high nitrogen
poop. One of
Joel Salatin's books has a chart on animal density based on their nitrogen output and that info can also help guide you. Too much nitrogen kills the soil and risks dangerous run-off, so it must be avoided.
6. I do hope you go for 5 paddocks, because if you do the math correctly, at 7 days/run, day one overlaps in the first run at 22 days rather than 29 days if you only have 4. Of
course, seasons and eco-systems affect whether the 28 days of recovery works in the first place. I believe it was Paul who suggested that was why an attached deep mulch run was useful as a back-up so if you felt your paddock needed more recovery time, you wouldn't be forced to use it regardless. (if it was someone else, my apologies)
7. Multi-species - now you're getting even more complicated. Some stacking may happen as different birds like different plants although if they're all feathered there's going to be a lot of overlap.
Unfortunately, I've got to run, but hopefully this will get the discussion started. I've had chickens for years and mostly use a portable
shelter system due to high predator pressure, but there are definite downsides to this - particularly the work involved). From that
experience though, *always* have back-ups and spare infrastructure. You never know when you may have a sick/injured bird, or unexpected gifts (will you please take my son's 4H birds?) that need at least temporary housing.
J.