Three bird species have the pecularity to have the lower bill longer than the upper, the Black Skimmer of America, the African Skimmer and the Indian one. Additional specializations are associated with this bill conformation, including the strengthening of the neck muscles, and the attachement of the skull to the neck by bony processes; the vertical shape of pupils to protect the bird from sun's glare off the water during nocturnal fishing; and the way that the wing strokes are kept above the bird horizontal plane.

Austin Jr, O.L, (1961), Birds of the World, Golden Press, New York, p 137