I don't know if this is a coincidence or not, but I changed over my breeders to Gamebird Layer (Purina Layena) from GBS (Purina Startena BDM 50, medicated is all I can get). Rather than having two bags of feed, I wanted to use up the Layer so I can go all GBS. Anyway, I noticed that the birds are drinking and eating less Layer than GBS. Nothing has really changed recently. They are inside the house and their overhead light is on a timer. They do have a window, so the actual daylight has been getting shorter, but the bedroom light comes on at 6 and stays on until about midnight, so they get about 16 hours of light a day. Laying hasn't changed. The only thing that has changed is their feed. I switched them over gradually over a few weeks, mixed 2/3 GBS to 1/3 Layer, then 50/50, then 25/75, then this week it's all Layer.