"Bill-Feaking" is a falconry term describing the act of a bird's wiping its bill on a branch or hard object in attempts to clean it. Raptors and Corvids often "feak" their bills to maintain and fine-tune their condition. Since beaks are comprised of keratin, they are constantly growing and need to be shaped to adapt to their specific food source. Birds can also display bill-feaking when they are annoyed or their activities are disrupted and they become nervous or agitated.