So people don't think of it much, but birds need to shed their feathers just like dogs shed their hair or snakes shed their skin. That's what's going on here below. The hen in the foreground is molting, or growing new feathers. Unfortunately she chose to do so in a rainy, cold snap. It got down to 18 F that night, but she made it through okay. All mature birds will molt in the fall. This was one of the things old time breeders selected for: chicken molts in late fall - good, chicken molts all her feathers nearly at once - great. These characteristics correlate into the most productive hens - more egg for your scratch.
During the course of the year, feathers get broken, worn down, or simply wore out. The feather functions as the chicken's coat, keeping the hen (or rooster) warm in the cold, shedding rain with oil spread during preening, keeping the skin from drying out or getting sunburnt - you get the idea. A hen's laying slows down greatly during this time, and may even stop completely, but will ramp back up when she's done. This is why commercial laying CAFO's induce forced molts through stress - the producer gets a boost in production when the older hens naturally start slowing down their laying. It resets the flock. Ironically in organic CAFO (free range) operations, the regulations practically prevent forced molting the hens into a molt, so they're typically just sent to the slaughterhouse after the first lag in production, instead of getting a second period of laying out of the ladies.
We just let the hens do their thing here at our place.