How old are your layers? Are they heading into a molt (about 18mo)? Is the daylight length SO short that they're just resting for a bit? Do they have enough water?
I found if I kept 2 additional water sources in the run (not just the one, but two) - my egg production skyrocketed! Was getting 1 egg a day from 5 pullets - after adding additional waterer, consistently getting 3 eggs a day from 5 pullets. So someone was 'guarding' the water! Since I'm getting 3 eggs daily from 5 pullets, that means someone (or two or three) are still laying daily. Couldn't tell you who...but I'm thankful!
We've also had a VERY mild season thus far - daytime highs in the 40's, lows in the 20's (for northern Illinois in December, that's mild!) - and I think that helps. I'm also making sure they're getting enough protein daily...a bit of an extra lunchtime treat while I'm home for lunch! Yogurt, mealworms, scrambled eggs, spinach, homemade breads, oatmeal, raisins....you name it, it all gets shared with the chickens! So between the extra protein AND the extra water, we're laying well here!
BTW - pullets are Black Java's from Garfield Farm Museum, LaFox, IL. Wonderful birds.