Outside ambient air temperature, or ambient coop temperature. We all know that the amount of daylight affects egg laying, but temperatures also play a role. The colder it gets, the more energy a hen uses to stay warm as opposed to producing and laying an egg. The two go hand in hand. Too hot and your chickens may not lay as well either. Some breeds are affected more by one than the other. If for no other reason than to satisfy curiosity, keep track. If a strain of your chosen breed or breeds show that they can lay during even the coldest and shortest days, then that is a good thing for the backyard or small flock owner. Its one thing to "notice" a trend, its quite another to have the hard facts and be able to back up your hunches.
