Preening is feather care. A duck uses its bill to clean, align, and maintain its feathers so they continue doing their jobs.
Why it matters
Well-maintained feathers help insulate a duck, support flight, and keep the feather layer in good condition around water. During preening, a duck carefully works through different parts of its plumage—often with impressive flexibility.
So when a duck looks as though it is fussing over every feather, that is not vanity. It is maintenance.