If you are a newer chicken owner, like me, you might be experiencing a serious decline in the amount of eggs you get daily with a bit of concern. Don't worry, I completely understand your pain. You finally get the girls laying, celebrate your first egg like an engagement ring, and then blammo no more eggs. I'm here to tell you that this is pretty normal when it comes to chickens and winter, even chickens in California winter.
There are many reasons for chickens to stop laying from poor flock health to a diet that is lacking. However, in winter the most likely reason for a slow down in overall egg production are less hours of sunlight and molting. This is a natural part of a chicken's life and not something to become overly concerned about. You can add light to your coop and runs to keep your chickens laying, but remember that chickens have a finite number of eggs they are going to lay in a lifetime and if these are your pets (i.e. backyard chicken raising) you may just let them sit this season out.
My six girls are all into laying age. However, we are currently getting only 1-3 eggs a day. Some days perhaps none. I'm not too concerned as we still have enough eggs for our family of three. One thing to keep in mind is that protein is essential all year, but even more in winter. Offer your girls some extra meal worms or red wigglers, a can of tuna here or there, spinach and other leafy greens that they can't find during this time of year and a high quality feed with a good protein content of 15-20%. Scraps of meat from the kitchen, leftover beans and sunflower seeds are also great.