Papilla
A small, brightly coloured, fleshy knob in the mouth of a nidicolous nestling, combining with the colours of the gape to guide the parent in placing the food which it brings to the nest. The number of papillae varies from one species to another and they are not present in all those with nidicolous young.From Peter Weaver's Birdwatcher's Dictionary
Copyright © 1981 by Peter Weaver