https://books.google.com/books?id=sBMGN_Ia500C&printsec=frontcover&source=gbs_summary_r&cad=0#PPA105,M1%7CPages 105–106] In birds of prey, the membrane also serves to protect the parents' eyes from their chicks while they are feeding them, and when peregrine falcons go into their 200 mph dives, they will blink repeatedly with their nictitating membranes to clear debris and spread moisture across the eyes.