All birds are born with a circadian clock—an internal time-keeper, you might call it. This circadian clock tells the bird the right time to lay, the best time to molt, and in some species, the proper time to fly south for the winter.
Our hens suddenly hunker down, slow or stop their egg laying, and seemingly break out in pillow fights every night.
To prepare for winter, their bodies are telling them to drop all the old feathers and regrow new ones for better insulation and weatherproofing. (And yes, this still applies to chickens in warmer climates with mild to no winters; they still need a new coat for the rainy season.)
Avoid subjecting them to physical, mental, or environmental stress, such as changing their diets, moving them to new quarters, or introducing new flock members.
If you make your own chicken feed, increase the protein content a little bit to help with feather regrowth. Or, offer your chickens high-protein snacks like dried mealworms, dried grubs, sunflower seeds, hemp seeds, or pumpkin seeds.