Avian beaks or bills are made of keratin, the same material that forms human hair and fingernails. In most birds this keratin layer grows continuously throughout life and is worn down by normal activity.
Raptors’ beaks are worn down by the tough scales, feathers, bones and fur of the prey they eat. Feaking, rubbing the beak clean on stones, branches or other hard surfaces after eating, removes the blood and other debris from the beak as well as “trimming” the beak. Raptors in captivity, whose beaks are not worn down through diet and feaking in a natural environment, often must have their beaks trimmed by their handlers.
The beak of a bald eagle (Haliaeetus leucocephalus) has a hook at the end used for tearing their prey. The upper mandible has a sharp edge that overlaps the lower mandible resulting in a scissors-like action as the eagle eats. Bald eagles use feaking to maintain this impressive beak in prime condition.
This bald eagle was along County Road 91 near Lookout CA (Modoc County).