Fortunately, if the feather was lost naturally, the owner doesn’t miss it and has probably already regrown a replacement. Birds lose worn-out feathers here and there, or they may lose many during a longer molt and completely change seasonally from, say, lemon yellow to subdued tan in the case of a male American Goldfinch.
The typical feather is made up of a central shaft (rachis) on either side of which are vanes. The vanes are then made up of tiny paired branches called barbs that further branch into even tinier barbules. These hooked barbs and barbules attach to each other even more efficiently than Velcro (engineers have studied feathers for inspiration on new adhesives) and create the flattened, usually curved surface of the vane.
Feathers require daily care to keep their wearer protected and aerodynamic. Bathing in water or dust removes dirt or parasites, after which a bird uses its bill to spread a waxy substance from its uropygial or preen gland at the base of its tail all over its feathers. Feathers are already waterproof and strong because of their barb and barbule structure, but this treatment keeps them flexible and lubricated. Whether you’re observing ducks, hawks, or sparrows this winter, keep an eye out for preening. It’s a daily or twice daily ritual for most birds, and witnessing it will give you further insight into the life of a bird.