For what it is worth, I have read Storey's Guide and many, many posts on BYC Duck Forum about egg laying. I have learned much.
My ducks taught me that most of them (10 female runners) don't lay if they are too cold.
A few weeks ago, because two were molting and were shivering as the temperatures dropped into the 20's I moved them into a 60 sf pen in the walkout basement. Temperatures there are in the mid 40s give or take.
At that time they had been giving us three eggs a day, for weeks. I reckoned it was the shorter daylength.
It's been about three weeks, and we are now getting eight eggs a day. Yes, they get a little more light, but they are also more perky, and just look a little better. They go outside a few times a day, until they start acting too cold. Some days (mid 30s, usually, and sunny), they like to stay out in the duck yard all day. But at night, they come in.
It's been less expensive to just have them in the basement than try to figure out a safe way to heat their double-walled, insulated duck house. With our layout, it's pretty easy to get them outside and into the different fenced areas we have for them.
When it comes to laying eggs, I think in terms of energy. If the duck is using all her energy to stay warm, or fight off an infection or parasite, or stress, she doesn't have anything left for forming an egg. She needs the right nutrition and environment.
That said, some ducks just take quite a while to start laying. Some of mine started at 16 weeks, but they weren't all laying until 22 weeks, and that was in full summer. I'm still not getting ten eggs, so either they are not laying daily (quite likely) or we have a couple that still aren't back to laying.
