Okay, yesterday afternoon our 6 month old Black Sex Link chicken died in the coop floor. She seemed fine the day before and during the morning. There were no apparent injuries and no signs of anything. She was free to go out into the run or stay inside. There is a lot of venting and a fan blowing the warm air out of the coop. Yesterday was a cooler than usual day with overcast and rain off and on. The other chickens in the same coop and run are fine. What might cause this? We haven't had this before.