True "free range" means that the chickens run perfectly freely, no fences anywhere.
"Day range" means that the chickens range (usually free range or confined on pasture (as opposed to mostly bare dirt), rotating pastures) during the day but are safely confined at night.
"Pastured poultry" refers to chickens raised on pasture. Usually, this requires pasture rotation, using a moveable coop and electrified fencing, so that the hens are not in contact with the same ground for eight weeks at a time (the time it takes Nature to "sterilize" the ground, destroy parasites, and let the pasture recover). Pastured poultry can be day ranged with a moveable coop or confined to moveable pens. Moveable pens are usually moved daily. Moveable coops about once a week, since the hens are not confined in a small pen.
The set-up you show appears to be a stationary, confined, pen. As others have noted, the chickens will denude 400 square feet very quickly. The buildup of manure will create a cycle of worms and other parasites, as well as diseases, in your flock, which would not be a problem in a well-managed pasture rotation. And sooner or later, the predators WILL get your chickens if you rely on chicken wire. It's not a matter of "if", it's a matter of "when". Chicken wire is not an effective deterrent or prevention. And, once a predator finds your easy "lunch counter", they'll be back--some will even bring their friends. You can lose your whole flock in no time, and in a very tragic and ugly manner indeed.
Electrified poultry fencing, properly used, is easy to move about, and it is very effective against most every ground predator. You can buy it (see "Premier" or "Kencove" websites, for example, or you can learn online how to electrify most any fence.
We have found that, the most effective protection for overhead predation is a good rooster--it's a rooster's "job" in the flock to be on guard and warn the hens of overhead predators, and a good rooster takes the job very seriously. The roosters have unique calls for each bird. In fact, the call for a hawk sounds very much like "Hawk!!!" The hens learn quickly when he's warning is just a warning, or when he's serious.
The hens, though, must have readily available cover to run under or into, when the rooster warns them of imminent danger, so the hawk or whatever won't be able to get at them. Brush and bushes scattered about the pasture work, as do small home-made covers scattered about. Hawks and other overhead predators can drop out of the sky pretty quickly, so the hens need to be able to get under cover quickly.
There are lots of ideas out there online, and there are great books out there, too.
If you are raising a backyard flock and absolutely can't rotate them in different parts of your yard, you're pretty much stuck. But you don't have to have the traditional smelly, dirty, infection- and parasite-ridden chicken yard of days past. You can alleviate the problem, to some extent, by adding about four inches deep aof good alfalfa or grass hay over all the ground in your 400 sq ft pen. The chickens will have a ball foraging through it, reducing stress and boredom, and actually adding to their daily nutrition. The grass will also help keep their little yard clean. And it will attract earthworms and grubs into the ground in the pen, which are delicious and nutritious high-protein treats for your chickens. When the hay gets dirty, simply rake it up, put it in your compost pile, and replace with clean hay. The old hay, complete with chicken poop, will make fabulous compost for your garden or flower beds.
Hope this helps.
Chickenladyk
