How are feathers digested by raptors?

In order to determine the cause of the evident degradation of feathers from ingested prey in pellets regurgitated by raptors, in vitro digestions of whole feather barbs by pellet extracts, pepsin or trypsin were carried out. The material was analysed by using biochemical and electron microscopic methods. The results show that the changes in the feathers which occur in the stomach of the Falconidae do not arise from digestion of keratin but from hydrolysis of protein acting as a cement matter in the feather.