Male and female American white pelicans (Pelecanus erythrorhynchos) develop a fibrous keel (knob or horn) on their culmen (top bill) during the breeding season. The keels can be up to two inches high. After the pelicans mate and lay their eggs, the keels shed. The purpose of the keels is not known, but may be involved in attracting mates. This pelican with its large keel was swimming on Baum Lake (Shasta County CA).