Went out to feed and water my chickens and one was dead and stiff as a board. They are Rhode Island reds and supposedly do very well in much colder weather. Coop is open other than an igloo doghouse I put in last winter. For some reason only one bird gets in it and the other 5 sleep on a stand I built for a 50 gallon water drum. The dead one appears to have bedded down on the ground last night (a first) and froze. Any input on why she would just sit there and freeze?