Puzzling Chickens

My chickens are acting weird. They're laying eggs outdoors and refusing to come in at night, preferring to sit out in the freezing cold. I have checked the coop for pests, vermin, mites, and anything else I can think of. I changed all the bedding. What are they afraid of? What is going through their tiny avian brains? If anyone has ever experienced this phenomenon with chickens before, I'd love to know it. The guys at the Feed-n-Seed store (normally my source of fowl information) were mystified. It was cold enough last night to freeze the water in their coop, yet they stubbornly sat outside until I bribed them with some corn.

The Great Chicken Mystery is looking for a solution...