Preening is the simplest and most common of feather care activities and is very important in maintaining healthy feathers. It involves two different actions, nibbling and stroking. All other feather care activities seem to be a prelude to preening, or at least end in a bout of preening. Preening serves the function of returning feathers to their correct position and form and often involves the addition of oil to the feathers from the Uropygial gland. Wiping is simply wiping the feathers with the bill, pressing them into place and perhaps spreading some oil over them. Nibbling is a more serious attempt to put the feathers back into pristine condition. The bird uses its bill to nibble along the edges of feathers straightening them out and ensuring the barbules are all zipped up.