In order to fly at peak performance, birds must carefully maintain their feathers. This means removing dirt, excess oil, and parasites. Birds do this by running their bill from the base of a feather to the tip, a process known as preening. In addition to removing debris, preening also realigns feathers, improving their aerodynamic performance.
This video accompanies Chapter 4, Feathers and Plumages, Handbook of Bird Biology, 3rd Edition from the Cornell Lab of Ornithology and Wiley Publishing.
Recorded by Katherine S. Lauck, Macaulay Library