The photos show a mushroom that would appear to in the Agaricus genus, a group which includes the common "button" mushroom you see in the supermarket. I do not think it is a shaggy parasol, which is in a different group. Agaricus mushrooms sometimes can be identified by the chocolate brown spore print. The gills start out a pink color before turning brown from the spores. Agaricus includes some of the best edible gourmet mushrooms such as the prince (A. augustus), but also includes several mildly toxic species that go under "the lose your lunch bunch" group. If I were you, I would mulch the area, keep it moist and keep the chickens away from it. Then if you get more mushrooms, take a spore print (it should be brown) . You might have a valuable species like Agaricus bitorquis, one of the best one for the table and one that I grew on manure
compost years ago. This species is delicious and loves lime-rich, compacted soil around barns. You might also have Agaricus hondensis, a mildly toxic species. Keep careful notes on the odor and look for yellow staining on the cap and stem, because this will help you determine if it is a good edible species. "Mushrooms Demystified", by David Arora, has a lot of info on the agaricus group. Keep posting more photos and info here, too.