Reading the red

For a cardinal, red feathers are a kind of biological report card. 

The richer the color, the more likely the bird is to have a strong immune system, sharper cognitive function and a longer life. For Geoff Hill, a professor in the Department of Biological Sciences, those patterns have opened the door to a much larger question: Can the color of a bird’s feathers reveal something fundamental about how cells function, age and decline? 

“The redder birds are the better birds,” Hill said. “They have better immune systems, better nervous systems and better cognitive function. They sing better songs. They show lower oxidative stress, which means things are running better within every cell of their body.” 

Hill’s latest National Science Foundation-funded project will take that question into the cell itself. 

Working with Matt Toomey of Michigan State University and Yufeng Zhang of the University of Memphis, Hill is investigating the biological machinery that produces red coloration in Northern Cardinals and house finches. 

The work begins with a surprising fact — These birds do not become red by eating red pigment. They eat yellow pigments, then use enzymes inside their cells to convert them into red. Hill and his collaborators believe the efficiency of that process may reflect how well the cells are functioning overall. 

“If you’ve got high cellular function, then it just happens,” Hill said. “Your cells can do this. If you have low cellular function, your cells can’t do it very well and it shows up in your plumage.” 

That idea marks a major shift from how scientists once explained bright coloration in birds. 

The long-standing theory held that colorful pigments were scarce. Under that explanation, the brightest birds were the strongest competitors, able to find and consume more of a valuable resource. Hill once accepted that explanation, too. 

“I was totally wrong early on, but that’s science,” he said. “You get ideas, work on them, find out they’re not right and get new ideas.” 

Research pointed Hill and his collaborators in another direction. The pigments were not scarce enough to explain the patterns they were seeing. What mattered more was not how much pigment a bird consumed, but what its cells could do with it. 

About a decade ago, the team helped identify the genes and enzymes birds use to turn yellow pigments into red ones. They have since recreated that process in cultured cells, inserting the necessary genes and supplying the cells with the same yellow pigments birds consume. The cells then produce red pigment, much as they would inside a bird. 

“It’s like magic to me,” Hill said. 

That magic comes from the specialized skills of his collaborators. Toomey brings expertise in pigment chemistry and proteins, while Zhang has the cell-culture experience needed to recreate the process in the lab. The cell cultures allow the researchers to alter specific aspects of cellular function, then measure how those changes affect red pigment production. 

“This has never been done before in the world of signaling in birds or pigment coloration,” Hill said. “Now we’re down into the mechanisms, testing specifically how it would work.” 

The research may also help explain why female birds often choose brighter males. A female may not be responding to the color alone, but to what it reveals about a potential mate. A male with strong cellular function may pass those traits to his offspring. He may also be a more capable partner in species where both parents gather food and care for their young. 

“You pick the good bird, and you get benefits,” Hill said. 

The possibilities extend beyond bird biology. If red pigment production reliably reflects cellular health, it could give scientists a useful way to study how cells function, deteriorate and age. 

“Anybody who wants to extend human lifespan should be really interested in how red pigments in a bird would predict how long they live,” Hill said. 

The project is basic research, designed to build knowledge rather than produce an immediate treatment or product. Hill argues that major advances often begin with questions that seem far removed from their eventual applications. 

“Who would have ever said, ‘I’m going to study red coloration in birds and figure out why we get old and die?’” Hill said. “But it sure gets interesting when it comes back around.” 

That is why, for Hill, the project is about more than red birds. 

“Funding basic research is important,” he said. “Even if you don’t care why birds are red, you might be interested in discoveries that allow you or your kids to live 20 or 30 years longer.”