My babies continue to avoid their coop during daylight hours, except to lay. But some do seem to have lost quite a lot of weight. I have chosen to not add light or heat, and they have a protected and covered area as well as a large back yard. This has been the harshest winter I recall in the 17+ years I've lived in SW WA. Now that the severe cold has broken for a while, it is very wet. And the large grassed area is mostly just mud now. Almost no greens available for them to nibble on. I feed them organic layer pellets (and the chicks are on organic chick starter), along with a varied home-made non-gmo scratch a couple of times a day, and chopped up leftovers of my summer and autumn harvests.
So - as this is my first winter with my chickie-babes, I am just watchfully waiting and looking forward to winter being over. It's rather stressful, though! And I sense that they are somewhat stressed too.