Feathers are light and have very good thermal stability. So in winter, down jackets are popular among people. However, woodpeckers pluck out the feathers that cover their bodies and keep them warm. It’s only for their young.
Woodpeckers willingly pluck the feathers off their bellies that directly contact the eggs during incubation. This bare area is fluid-filled and highly vascularized, making it possible for the birds to transfer heat directly to their eggs when incubating. This featherless area on their chest that they press against the eggs to keep them warm is called a brood patch. In most birds, a brood patch on the abdomen is automatically developed, but woodpeckers pluck their feathers from their own bodies. Moreover, their beaks are strong enough to drill holes in trees.
For their young that are not yet born, woodpeckers endure the painful process of picking out their feathers with their strong, sharp beaks. Their brood patches are the traces of their sacrifice.