Last night it was about 18 degrees here in central New Hampshire. My 10 hens have been in the coop for several days - the coop is in the barn, rubber mats over wood on the floors, and pine shavings over the rubber mats. They have plenty of food, and water that's on a defroster (heated tin) Anyway, we went out this morning and one of my buff orpingtons was dead on the ground inside the coop! It clearly didn't fall off the perch and break its neck - it was off away from the perch. These hens are 6 months old. They are eating layer pellets, and get scratch too, as well as other treats like grapes and a supplemental kibble. any thoughts? I've read from so many people that the chickens will be fine in cold temps - but what else could have happened last night? thanks in advance other info: we were getting 5-8 eggs daily (not all of the hens had started laying yet), including one hen that appears to be laying rubbery eggs that break on a daily basis.