It is well known that birds frequently attract mates by a ritual display of feathers or other ornaments. The colors for these displays are either derived from pigments, such as carotenoids, or photonic crystalline arrangements near the surface of the skin, feathers, or other ornaments. Add to this the fact that many birds can perceive light in the near-ultraviolet end of the visible spectrum and the range for these visual displays is extended. In a spectrophotometric and microscopic study by Birgitta Dresp and Keith Langley, it was demonstrated that a unique arrangement of crystal-like structures near the surface of the beak horn of the King penguin (Aptenodytes patagonicus) most likely accounts for a photonic effect that probably plays a role in their mating rituals.