Old feathers are replaced in a specific order
Q It seems miraculous that hens change their coats. How do feathers grow?
A Victoria Roberts says: The moult is usually hormonally initiated by shortening days in autumn. Good layers tend to moult quickly as they seem to have a better, faster metabolism than poor layers. The old feather is pushed out of the feather follicle by the new one coming through. They are known as pin feathers due to the blood in the feather sheath. The blood nourishes the feather — which is made of keratin, like our nails and hair — until it has reached its genetic size, then the blood is resorbed back into the hen. There is a certain pattern to this replacement: you may have seen that the feathers are placed in lines or tracts which allows muscular movement of the whole tract when displaying or threatening. These are replaced in a specific order so that the hen still has some insulation from the old feathers.
New feathers are called pin feathers due to the blood in the feather sheath