They are in an enclosed run 80% of the time. The last time they free ranged was Sunday.were they outside or inside? if outside I might say they found something, bug, fungus, weed, that should not be eaten and ate it anyways. I've had that happen on a number of occasions. twice I actually watched them hunt down the bad bug, while I tried to distract them and get it first...
if they're inside, check their feed bag thoroughly for signs of mold or mildew. usually that doesn't act as fast, but it's possible.