A rare yellow northern cardinal spotted in Alabama in 2018 became an internet sensation and opened millions of people’s eyes to a spectacular power of genetic mutation.
Now, Geoffrey Hill, an ornithologist at Auburn University who helped identify Alabama’s yellow cardinal, has released a 15-minute YouTube video breaking down the science behind that genetic mutation, and how to tell if a bird you’ve seen in the wild is a yellow cardinal or not.
“Because I spent my life studying bird coloration, I can explain this fascinating phenomenon and answer some of the most frequently asked questions regarding yellow plumage coloration,” Hill said in the video.
Hill, a leading expert on bird colorations, has written books on the topic and hopes that interest in yellow cardinals can spark people’s curiosity to learn more about their winged neighbors.
“The yellow cardinal is a great entry point for learning about bird coloration and the basis for variation among birds in their coloration,” he said. “Differences between young and old birds, male and female birds, and variation within an age and sex class.”
What makes a yellow cardinal yellow?
Hill said there hasn’t been enough genetic research to know exactly what happens in a yellow cardinal, but he and other ornithologists have a general idea.
In the video, Hill explains that most cardinals have an enzyme in their bodies that converts yellow pigments in the foods they eat – plants and insects – into red feathers.
However, the yellow cardinals likely carry a genetic mutation that prevents them from producing that enzyme. What in most cases are brilliant red feathers become a bright yellow instead because of the missing enzyme.
“Because this has never been studied in detail, genetically, we have to presume,” Hill said. “But we know that there’s almost certainly a mutation, probably a point mutation, that means a single letter in the genetic code is changed.”
“If you randomly change a letter in the genetic code, it’s almost certainly going to be bad. Very, very rarely will be good.”
But in this case, the “bad” seems to be manageable. It simply changes the birds’ coloration.
Hill said he and fellow researcher Kevin McGraw, now at Arizona State University, conducted a biochemical analysis of a yellow cardinal feathers collected in Louisiana in the late 1980s that seems to support that conclusion.
“We confirmed that the chemical composition of those feathers was just what you’d expect if there had been a disruption in the pathway leading to red coloration,” Hill said.
How to confirm what you’re seeing is a yellow cardinal
Bright yellow feathers and distinctive black mask around the male cardinal make it easy for many to identify, at least to people who know what to look for.
But for more novice birders, Hill has some tips.
“It’s really easy to mistake a typical female cardinal for that sought-after yellow cardinal,” Hill said.
Hill said typical female cardinals will have a reddish color on its tail and wings, but the bodies are usually a pale brown color that can look yellowish in certain light. Hill said that if the bird has any red feathers on its body at all, then it’s not a yellow cardinal, as the mutation makes those birds incapable of having feathers that color.
“There’s no red whatsoever in the feathering,” Hill said.
The video includes a visual guide for how to tell the yellow cardinal from female cardinals or other birds.
Goldfinches are also sometimes mistaken for yellow cardinals by inexperienced birders (including some who sent photos to this reporter’s inbox), but those lack the distinctive plume of feathers sticking up atop a cardinal’s head, as well as other differences.
Sightings on the rise, but still a rare bird
Since “Mr. Yellow” became famous in 2018, at least 10 other yellow cardinal sightings have been reported. That may be because more people now recognize what they’re seeing in a yellow cardinal, and because the rise of social media and camera phones makes it easier to document and share the sightings.
There was Sunshine, a yellow cardinal spotted in south Alabama in 2019. Hill said sightings have also been confirmed in Florida, Tennessee, Delaware, Arkansas, North Carolina, Louisiana and this week, in Illinois.
Hill said in 2018 the cardinal’s mutation made it a “one-in-a-million” bird, and he stands by that assessment.
“I think one in a million is a pretty good ballpark guess here,” Hill said in the video. “Cardinals are a tremendously abundant bird, and there’s well over 12 million, say, in eastern North America.
“And I think at any one time, there’s probably about a dozen yellow cardinals known in yards around the country.”
Yes, other birds also carry this mutation
Hill said the mutation that causes cardinals to appear yellow also occurs in other birds, but isn’t as easy to recognize.
“Cardinals have a few characteristics that make a yellow individual really stand out,” Hill said.
For example, cardinals molt only once per year, so they mostly look the same year-round. Other species, like the scarlet tanager, molt twice per year and regularly appear yellowish in the fall and winter and red in the summer.
In the video, he shows photos of a red-bellied woodpecker with a yellow, not red, nape, as well as a yellow scarlet tanager, and a yellow rose-breasted grosbeak.
“It’s not surprising [that this would occur in other species],” Hill said. “All that is required is a mutation that disrupts the pathway from yellow to red, and you end up with a yellow bird instead of a red bird.”
Hill said that house finches can also appear yellow, but for a different reason: stress.
“This is a different phenomenon,” Hill said.
“For reasons we don’t clearly understand -- and this has been my life’s work trying to understand this -- when [house finches] are in reduced condition, if they’re sick, if they are stressed in some way, the pathway to red feather coloration shuts down and they produce yellow and orange coloration. That doesn’t happen with cardinals.”
Yellow cardinals can reproduce
One of the questions about yellow cardinals is whether they would be accepted by females and successfully reproduce despite their unusual appearance.
Charlie Stephenson and photographer Jeremy Black, who observed and photographed the bird at Stephenson’s home in Alabaster, may have helped answer that question when they photographed Mr. Yellow feeding chicks in a nest after being observed spending a lot of time with a female cardinal.
But the chicks left the nest before Stephenson and Black could tell if they carried the same genetic mutation as Mr. Yellow.
Mr. Yellow, a cardinal with a rare genetic mutation spotted in central Alabama in 2018 and 2019, sits watch over two baby birds that are possibly his offspring.Jeremy Black Photography