(noun) The horny plate that appears as a bump at the end of the upper mandible of the bills in adult ducks, geese and swans. The nail helps these birds dig through mud when rooting for food such as mollusks, aquatic plants and aquatic insects. Depending on the species, the nail may be a contrasting color to the rest of the bill, making it an exceptional field mark, or it may be the same color and indistinguishable except for shape.
The nail is only found on adult birds. Young ducks, geese and swans develop an egg tooth that will help them break out of their shells when hatching, but they lose the egg tooth within the first day or two after hatching. The nail develops as birds mature.
Photo – Bill with Nail © Tomi