It's welded wire mesh. Lowes, Home Depot, hardware stores, amazon all sell it. I found the best source for me was my local Ace hardware store, I order by the 100 foot roll and it's much cheaper overall. Comes in various widths and hole sizes. For chickens 1/2" or smaller is best. It is on some of your coops already, rabbit hutches are often made of it. It's sturdiest when installed either with screws and washers (as opposed to staples) or sandwiched between two layers of wood screwed together.
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Looks like most or all of your structures are also prefab coops. If you are in this long term you will probably need something sturdier. They don't hold up real well over time. I wouldn't trust one in a hurricane at all. I'd use them for now, but have a plan for something sturdier in the future. A converted shed is often the most economical way to do it. Or just start making a list of must haves/ and things you hate about what you have, and plan to build what you want. That is ultimately what I did. And since I'm also in a hurricane state, mine is anchored with mobile home anchors.