Ultraviolet Beaks

Today is Penguin Awareness Day. Let’s discuss a feature of which we humans may not be aware, because of our limited visual perception. Our eyes can detect the visible light part of the electromagnetic spectrum, spanning the range from about 700 nanometers (red) to 400 nanometers (violet) wavelength.  Many birds, including penguins, see beyond this range into the ultraviolet portion of the spectrum.  Birds often have “hidden” markings that they themselves can see, but can only be detected by humans through artificial illumination.

King Penguin, Falkland Islands. Photo by Ben Tubby.

King Penguins are one species that have ultraviolet markings, as scientists have discovered. These large penguins are already stunning birds, with orange patches of color along their necks, ear regions, and the sides of their beaks. Recently, scientists delved deeper to detect ultraviolet patches are also positioned along the lower bill. Both the visible and ultraviolet colors appear to play a role in attracting mates.

How do King Penguins produce ultraviolet colors? The answer is multilayered reflector photonic microstructure. Essentially, the outer layer of the beak contains alternating layers of high refractive index and low refractive index materials. Reflected light from the different layers interacts to bounce back wavelengths in the ultraviolet spectrum. Research by Dr. Birgitta Dresp-Langley and colleagues has revealed that King Penguin beaks have a layer filled with special folded microstructures and intervening filaments
of β-keratin. These markings help indicate maturity, and may also be attractive to other penguins.  As a King Penguin grows, the ultraviolet hue of the beak markings increases. Surveys of wild penguins  show they are strongest in recently formed male–female pairs. When scientists hid the ultraviolet markings by painting a layer of varnish over a penguin’s beak, those birds had a harder time finding a mate – perhaps the equivalent of the penguin hitting the local watering holes without enough lipstick or cologne!

King Penguin, Falkland Islands. Photo by Ben Tubby.

References:

Dresp, B., P. Jouventin, and K. Langley. 2005. Ultraviolet reflecting photonic microstructures in the King Penguin beak. Biology Letters 1: 310–313.

Dresp, B, and K. Langley. 2006. Fine structural dependence of ultraviolet reflections in the King Penguin beak horn/  The Anatomical Record Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology 288: 213-222.

Jouventin P., P.M. Nolan, E.S. Dobson and M. Nicolaus. 2008. Coloured patches inXuence pairing in king penguins. Ibis 150:193–196