Over 400...! That seems to transcend "backyard" a little.

But that's very neat. One of my fondest memories from when I was little was this giant chicken barn in my grandparents' back yard. It hadn't been in use for years but there were still tons of chicken feathers everywhere. It had kind of a magical feel for me. And while many childhood memories diminish as we grow up, that barn was objectively huge. There must have been a commercial operation there at some point, and it clearly didn't involve battery cages.