I had an interesting experience when I arrived home late (about an hour after sundown), and went to shut my 3 birds in. Two of them were standing up with their eyes open and one was under the coop (She came out when she saw my flashlight). I did check them over, and did not see any signs of injuries. After some sweet talking and petting, they all three settled down on the roost.
Would not being shut in at the usual time be enough to scare them? If not, I'm thinking that maybe there was a predator around somewhere. Only, I can't think what predator (given time) would not have harmed at least one of the chickens. Anyhow (if my parents ok it), I think I will ask one of out neighbors to shut them in next time I'm going to be home late.