Being Red

Holding up a parrot feather in his laboratory, Kevin McGraw sees more than the intertwined strands of barbs emanating from a quill. He sees evolution at work, eons of development that have made the feather the most distinctive characteristic of a bird.

For example, feathers protect a bird from the elements, insulating it from the cold and heat. They also help birds stay dry in rain and snow. Lightweight, yet very strong, the feather’s primary function is to help a bird take flight. Wing feathers expand the wing surface during flight, increasing lift. Relatively large tail feathers function as rudders.

But what really intrigues McGraw, an assistant professor in Arizona State University’s School of Life Sciences, is the color of a feather. How does a feather obtain its color? And what does it mean for the bird? he asks.

McGraw has studied the chemistry behind the colors of many birds, including songbirds like sparrows and finches. He has studied how barn swallows judge their mates (and make judgments about their fidelity to that mate) based on color. And he has studied the chemistry behind the bright colors of parrots.

A bird’s color can mean any of several things. It can signal male assertiveness within a flock, or it can be a marking of status. Knowing the behavioral context of color is important. But McGraw digs deeper. He digs down to the molecular level in an effort to understand what gives the bird its color.

McGraw uses an arsenal of high-tech equipment and methods in his lab to deconstruct the chemical makeup of a bird’s feather. What he has found is both beautiful and a bit baffling.

One of the ASU scientist’s recent discoveries showed that a novel set of molecules are at work to create the bright red plumage in parrots. To date, no one understands clearly why these molecules work the way they do.

“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.

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

What exactly is in the behavioral significance of bird colors? McGraw first got interested in that question while studying color as a form of individual communication within a species. For example, many birds use color to denote status as well as to attract a mate. McGraw wanted to understand more about what makes the colors of the birds possible. Then he focused on “deconstructing the color into its component parts.”

The work casts a new light on what is chemically responsible for the colors of birds. The findings defy previous assumptions and explanations for color variations in parrots.

“Evolutionary biologists have not really thought hard about parrot coloration,” says McGraw. “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.”

McGraw worked with Mary Nogare, a parrot fancier from Snoqualmie, Wash., on the study. Animals, like birds and fishes, commonly use biochromes like carotenoids to acquire red, orange, or yellow coloration. McGraw and Nogare found that these compounds, while in the bodies of parrots, are not responsible for the red colors in the parrot species they sampled.

The researchers 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.

They found a group of five molecules called polyenal lipochromes, or psittacofulvins. These molecules color parrot plumage red in all of the species studied.

McGraw says an interesting aspect of the five polyenal lipochromes is that the pigment is found only in the bird’s feathers. It is found nowhere else in the body of the bird. This indicates to the scientists that parrots manufacture these molecules internally and directly at the maturing follicles of the growing, colorful plumage.

The pigments also may play a valuable role in maintaining the health of parrots. McGraw cites an independent study on the parrot pigments. Results from that study suggest that the pigments can act as anti-oxidants to quench free radicals and potentially protect cells and tissues in the body from oxidative damage.

Now, McGraw says, he’s interested in learning more about the connection between the red colors and anti-oxidants within and among parrot species. He wants “to specifically explore the balance of naturally and sexually selected costs and benefits to becoming colorful.”

“Parrots are unusual among birds,” he explains. “Almost without exception they 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,” McGraw says. “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,” he adds. “Our goal is to learn why there is such a diversity from an evolutionary standpoint.”—Skip Derra