Flying Rainbows

Parrots, long a favorite pet animal, are attractive to owners because of their vibrant colors. But those colors may mean more to parrots than what meets the eye.

For more than a century, biochemists have known that parrots use an unusual set of pigments to produce their rainbow of plumage colors, but their biochemical identity has remained elusive. Kevin McGraw has uncovered the chemistry behind the colors of parrots. The ASU biologist describes on a molecular level what is responsible for their bright red feathers.

McGraw’s work casts a new light on what is chemically responsible for the colors of birds. It defies previous assumptions and explanations for color variations in parrots.

“Evolutionary biologists have not really thought hard about parrot coloration,” says McGraw, as assistant professor in the School of Life Sciences. “This research is exposing a whole new world of color communication in parrots and the potential physiological and biochemical roles of the new molecules we found in our work.”

Details of the work appear in a paper, “Distribution of unique red feather pigments in parrots,” by McGraw and Mary Nogare, a parrot fancier from Snoqualmie, Wash. The paper was published in the Feb. 16, 2005 issue of the journal Biology Letters.

Animals, like birds and fishes, commonly use biochromes like carotenoids to acquire red, orange, or yellow coloration. McGraw and Nogare found that these compounds are not responsible for the red colors found in the parrot species they sampled.

They used a chemical analysis technique called high-performance liquid chromatography to survey the pigments present in red parrot feathers. McGraw and Nogare collected and analyzed samples from 44 parrot species that have red feathers. Overall, there are some 350 species of parrots, 80 percent of which have red in their plumage. The researchers found a suite of five molecules, called polyenal lipochromes (or psittacofulvins), that color parrot plumage red in all of the species studied.

“We’ve uncovered a system where all red parrots use the same set of molecules to color themselves,” McGraw says. “It is a unique pigment found nowhere else in the world. We are fascinated at how parrots are able to do this.

“The fact that there is a single set of molecules unique to and widespread among parrots suggests that it is a pretty important evolutionary novelty. It is one that we should carefully consider when we think about why parrots are so strikingly colorful,” McGraw says.

“Parrots are unusual among birds. They almost without exception display fantastic colors but exhibit very little variation in color within a species—at least in colors visible to us. Parrots in general may not be using color in the classic cases of mate choice or competitive ability,” he explains. “Exactly why they are so uniformly colored remains an interesting mystery to us—one we want to investigate.”

“There is a sea of colors in birds,” McGraw adds. “Our goal is to learn why there is such a diversity from an evolutionary standpoint.”—Skip Derra