A New Pigment in Penguins
Color is one of the things that draws people to birds. If one is not filled with wonder upon seeing a pink flamingo, an iridescent hummingbird or a rainbow macaw, it may be time for some serous introspection. Not all colors are created by the same means. Birds use a dazzling array of biological strategies to create color. Many of these come from pigments. Melanin, a pigment that is also found in our own skin and hair, generates colors like grey and reddish brown. Porphyrins create colors including bright greens and reds. Some pigments come from external sources – carotenoids are made by plants, but birds like cardinals and goldfinches gain their colors by harvesting these pigments from seeds. Some pigments can even leave traces in the fossil record. The fossil penguin Inkayacu paracasensis preserves feathers with melanosomes, the organelles that hold melanin inside feathers.
Aside from pigments, colors can be generated by structure – created by the way the feather refracts light. An example is the blue color generated by nanostructures in the Little Blue Penguin. Birds can even produce colors outside the visual light spectrum. Many species, including the King Penguin, have ultraviolet markings that they can see but humans cannot (more on this in a future post).
Recently, Dr. Daniel Thomas and colleagues reported a new type of bird pigment known to occur only in penguins. This pigment is responsibly for the yellow “ninja mask” of the Yellow-Eyed Penguin (Megadyptes antipodes) as well as the rakish yellow plumes of the Eudyptes penguins (the group the includes Macaronis and Rockhoppers). It is also seen in the rich orange neck feathers of King and Emperor Penguins (Aptenodytes). Dr. Thomas and his team used Raman Spectroscopy to unravel the chemical composition of this pigment. Surprisingly, the composition turned out not to match any of the previously known major classes of color-generating chemicals (carotenoids, melanins, porphyrins, psittacofulvins and metal oxides).
One additional interesting implication reported in the study is that the pigment is most likely synthesized directly by penguins. This is because penguins will grow the brightly colored yellow or orange feathers regardless of their diet – we see them in penguins gobbling down fish, squid, or krill in different wild populations and in zoos where food is carefully regulated. So, it does not appear they are gaining the color from their food like flamingos, which turn white if they don’t consume certain invertebrate prey.
Thomas, DB, McGoverin CM., McGraw KJ. James HF, Madden O. 2013. Vibrational spectroscopic analyses of unique yellow feather pigments (spheniscins) in penguins. Journal of the Royal Society Interface:10, 20121065.