I've had several different types of mushrooms pop up in the area of my new chicken run (coop and run still under construction) and I would bet they will return at some point after the hens take up residence. Do I need to be concerned? Some are bright red, which I associate with danger. Some are humongous! This area is currently mostly covered with Saint Augustine grass, quack grass, sorrel, Bermuda grass, nutsedge, and dandelions. Plus the usual stuff that grows under big old oaks in north Texas. This land was reportedly a pear orchard before the subdivision was built in the 1940-1950's. The only soil amendments in this area for the past decade have come in the form of fallen leaves and dog droppings. I've raked it out, watered and mowed it back to lay out my coop and run, but nothing else.