Many people have egg production dropping at this time of year. It's very possible they are going through a molt too. Add the colder temps. and the shorter days... So at least you know it's not just you. I'd give a go of adding a small heat lamp w/red bulb if the temps. are cold there (and I'd think they were based on your location)....aimed toward the roosts. Maybe warmer, happier chickens will produce more eggs (unless they are molting...have you noticed feathers laying about?). Hang in there...spring will be here eventually.