This has happened before (last winter). My chickens virtually stop eating. They sit on their roost all day, under the infrared lamp. I put them out in the run, only to have them run back in and get back on the roost (sometimes after eating a tiny bit). They don't seem horribly thin when I feel their breasts and they look healthy enough. I worry though. Last year, they started eating again (I mean significant amounts) in about February, and soon after that, started laying eggs again.
Is this something others have seen? Are they conserving so much energy by not moving around and not laying eggs that they hardly need anything to eat?